MycoplasmaFrom Wikipedia, the free encyclopedia

Not to be confused with Mycobacteria.

Mycoplasma

Scientific classification

Kingdom: Bacteria

Phylum: Tenericutes  or

Firmicutes

Class: Mollicutes

Order: Mycoplasmatales

Family: Mycoplasmataceae

Genus: Mycoplasma

Nowak 1929

Species

Mycoplasmosis

Classification and external resources

ICD-10 A49.3

ICD-9 041.81

Mycoplasma refers to a genus of bacteria that lack a cell wall.[1] Without a cell wall, they are unaffected by many

common antibiotics such as penicillin or other beta-lactamantibiotics that target cell wall synthesis. They can

be parasitic or saprotrophic. Several species are pathogenic in humans, including M. pneumoniae, which is an important cause

of atypical pneumonia and other respiratory disorders, and M. genitalium, which is believed to be involved in pelvic inflammatory

diseases.

Contents

  [hide] 

1 Origin of the name

2 Characteristics

o 2.1 Cell morphology

3 First isolation

4 Small genome

5 Taxonomy

6 Laboratory contaminant

7 First synthetic genome synthesized

8 See also

9 References

10 External links

[edit]Origin of the name

The name Mycoplasma, from the Greek mykes (fungus) and plasma (formed), was first used by A. B. Frank in 1889. He thought

it was a fungus, due to fungus-like characteristics .[2]

An older name for Mycoplasma was Pleuropneumonia-Like Organisms (PPLO), referring to organisms similar to the causative

agent of contagious bovine pleuropneumonia(CBPP).[3] It was later found that the fungus-like growth pattern of M. mycoides is

unique to that species.

[edit]Characteristics

There are over 100 recognized species of the genus Mycoplasma, one of several genera within the bacterial class Mollicutes.

Mollicutes are parasites or commensals of humans, other animals (including insects), and plants; the genus Mycoplasma is by

definition restricted to vertebrate hosts. Cholesterol is required for the growth of species of the genus Mycoplasma as well as

certain other genera of mollicutes. Their optimum growth temperature is often the temperature of their host if warmbodied (e. g.

37° C in humans) or ambient temperature if the host is unable to regulate its own internal temperature. Analysis of

16S ribosomal RNA sequences as well as genecontent strongly suggest that the mollicutes, including the mycoplasmas, are

closely related to either the Lactobacillus or the Clostridium branch of the phylogenetic tree (Firmicutes sensu stricto).

[edit]Cell morphology

The bacteria of the genus Mycoplasma (trivial name: mycoplasmas) and their close relatives are characterized by lack of a cell

wall. Despite this, the cells often present a certain shape, with a characteristic small size, with typically about 10% of the volume

of an Escherichia coli cell. These cell shapes presumably contribute to the ability of mycoplasmas to thrive in their respective

environments. Most are pseudococcoidal, but there are notable exceptions. Species of the M. fastidiosum cluster are rod-

shaped. Species of the M. pneumoniae cluster, including M. pneumoniae, possess a polar extension protruding from the

pseudococcoidal cell body. This tip structure, designated an attachment organelle or terminal organelle, is essential for

adherence to host cells and for movement along solid surfaces (gliding motility), and is implicated in normal cell division. M.

pneumoniae cells are pleomorphic, with an attachment organelle of regular dimensions at one pole and a trailing filament of

variable length and uncertain function at the other end, whereas other species in the cluster typically lack the trailing filament.

Other species like M. mobile and M. pulmonis have similar structures with similar functions.

Mycoplasmas are unusual among bacteria in that most require sterols for the stability of their cytoplasmic membrane . Sterols

are acquired from the environment, usually as cholesterol from the animal host. Mycoplasmas generally possess a relatively

small genome of 0.58-1.38 megabases, which results in drastically reduced biosynthetic capabilities and explains their

dependence on a host. Additionally they use an alternate genetic code where the codon UGA is encoding for the amino

acid tryptophan instead of the usual opal stop codon. They have a low GC-content (23-40 mol %).

[edit]First isolation

In 1898 Nocard and Roux reported the cultivation of the causative agent of CBPP, which was at that time a grave and

widespread disease in cattle herds.[4][5] The disease is caused by M. mycoides subsp. mycoides SC (small-colony type), and the

work of Nocard and Roux represented the first isolation of a mycoplasma species. Cultivation was, and still is difficult because of

the complex growth requirements.

These researchers succeeded by inoculating a semi-permeable pouch of sterile medium with pulmonary fluid from an infected

animal and depositing this pouch intraperitoneally into a live rabbit. After fifteen to twenty days, the fluid inside of the recovered

pouch was opaque, indicating the growth of a microorganism. Opacity of the fluid was not seen in the control. This turbid broth

could then be used to inoculate a second and third round and subsequently introduced into a healthy animal, causing disease.

However, this did not work if the material was heated, indicating a biological agent at work. Uninoculated media in the pouch,

after removal from the rabbit, could be used to grow the organism in vitro, demonstrating the possibility of cell-free cultivation

and ruling out viral causes, although this was not fully appreciated at the time (Nocard and Roux, 1890).

[edit]Small genome

Recent advances in molecular biology and genomics have brought the genetically simple mycoplasmas, particularly M.

pneumoniae and its close relative M. genitalium, to a larger audience. The second published complete bacterial genome

sequence was that of M. genitalium, which has one of the smallest genomes of free-living organisms.[6] The M.

pneumoniae genome sequence was published soon afterwards and was the first genome sequence determined by primer

walking of a cosmid library instead of the whole-genome shotgun method.[7] Mycoplasma genomics and proteomics continue in

efforts to understand the so-calledminimal cell,[8] catalog the entire protein content of a cell,[9] and generally continue to take

advantage of the small genome of these organisms to understand broad biological concepts.

[edit]Taxonomy

The medical and agricultural importance of members of the genus Mycoplasma and related genera has led to the extensive

cataloging of many of these organisms by culture, serology, and small subunit rRNA gene and whole genome sequencing. A

recent focus in the sub-discipline of molecular phylogenetics has both clarified and confused certain aspects of the organization

of the class Mollicutes.[10]

Originally the trivial name "mycoplasmas" has commonly denoted all members of the class Mollicutes. The name "Mollicutes" is

derived from the Latin mollis (soft) and cutes (skin), and all of these bacteria do lack a cell wall and the genetic capability to

synthesize peptidoglycan. Now Mycoplasma is a genus in Mollicutes. Despite the lack of a cell wall, many taxonomists have

classified Mycoplasma and relatives in the phylum Firmicutes, consisting of low G+C Gram-positive bacteria such

as Clostridium, Lactobacillus, and Streptococcus based on 16S rRNA gene analysis. The order Mycoplasmatales contains a

single family,Mycoplasmataceae, comprising two genera: Mycoplasma and Ureaplasma.

Historically, the description of a bacterium lacking a cell wall was sufficient to classify it to the genus Mycoplasma and as such it

is the oldest and largest genus of the class with about half of the class' species (107 validly described), each usually limited to a

specific host and with many hosts harboring more than one species, some pathogenic and some commensal. In later studies,

many of these species were found to be phylogenetically distributed among at least three separate orders.

A limiting criterion for inclusion within the genus Mycoplasma is that the organism have a vertebrate host. In fact, the type

species, M. mycoides, along with other significant mycoplasma species like M. capricolum, is evolutionarily more closely related

to the genus Spiroplasma in the order Entomoplasmatales than to the other members of the Mycoplasma genus. This and other

discrepancies will likely remain unresolved because of the extreme confusion that change could engender among the medical

and agricultural communities.

The remaining species in the genus Mycoplasma are divided into three non-taxonomic groups, hominis, pneumoniae and

fermentans, based on 16S rRNA gene sequences.

The hominis group contains the phylogenetic clusters of M. bovis, M. pulmonis, and M. hominis, among others. M.

hyopneumoniae is a primary bacterial agent of the porcine respiratory disease complex.

The pneumoniae group contains the clusters of M. muris, M. fastidiosum, U. urealyticum, the currently

unculturable haemotrophic mollicutes , informally referred to as haemoplasmas (recently transferred from the

genera Haemobartonella and Eperythrozoon), and the M. pneumoniae cluster. This cluster contains the species (and the usual

or likely host) M. alvi (bovine), M. amphoriforme (human), M. gallisepticum (avian), M. genitalium (human), M. imitans (avian), M.

pirum (uncertain/human), M. testudinis (tortoises), and M. pneumoniae (human). Most if not all of these species share some

otherwise unique characteristics including an attachment organelle, homologs of the M. pneumoniae cytadherence-accessory

proteins, and specialized modifications of the cell division apparatus.

A study of 143 genes in 15 species of Mycoplasma suggests that the genus can be grouped into four clades: the M.

hyopneumoniae group, the M. mycoides group, the M. pneumoniae group and aBacillus-Phytoplasma group.[11] The M.

hyopneumoniae group is more closely related to the M. pneumoniae group than the M. mycoides group.

[edit]Laboratory contaminant

Mycoplasma species are often found in research laboratories as contaminants in cell culture. Mycoplasmal cell culture

contamination occurs due to contamination from individuals or contaminated cell culture medium ingredients [clarification needed][citation

needed]. Mycoplasma cells are physically small – less than 1 µm – and they are therefore difficult to detect with a

conventional microscope. Mycoplasmas may induce cellular changes, including chromosome aberrations, changes

in metabolism and cell growth. Severe Mycoplasma infections may destroy a cell line. Detection techniques include DNA

Probe, enzyme immunoassays, PCR, plating on sensitive agar and staining with a DNA stain including DAPI or Hoechst.

It has been estimated that at least 11 to 15% of U.S. laboratory cells cultures are contaminated with mycoplasma.[who?] A Corning study showed that half of U.S. scientists did not test for mycoplasma contamination in their cell cultures. The

study also stated that, in Czechoslovakia, 100% of cell cultures that were not routinely tested were contaminated while only 2%

of those routinely tested were contaminated. (study page 6) Since the U.S. contamination rate was based on a study of

companies that routinely checked for mycoplasma, the actual contamination rate may be higher. European contamination rates

are higher and that of other countries are higher still (up to 80% of Japanese cell cultures). [12] About 1% of published Gene

Expression Omnibus data may have been compromised.[13] (Link into RNAnet showing contamination of GEO. Press plot and

drag blue crosshairs to expose links to description of experiments on human RNA samples). Several antibiotic based formulation

of anti-mycoplasma reagents have been developed over the years, including BM-Cyclin by Roche, MRA by ICN, Plasmocin by

Invivogen and more recently De-Plasma by TOKU-E.

[edit]First synthetic genome synthesized

CyanobacteriaFrom Wikipedia, the free encyclopedia

Cyanobacteria

Temporal range: 3500–0 Ma

Had'n

Archean

Proterozoic

Pha.

Oscillatoria sp

Scientific classification

Domain: Bacteria

Phylum: Cyanobacteria

Orders

The taxonomy is currently under

revision[1][2]

Unicellular forms

Chroococcales(suborders-

Chamaesiphonales an

dPleurocapsales)

Filamentous (colonial) forms

Nostocales (= Hormogonales or

Oscillatoriales)

True-branching (budding over

multiple axes)

Stigonematales

Cyanobacteria (English pronunciation: /saɪˌænoʊbækˈtɪəriə/; also known as blue-green algae, blue-green bacteria,

and Cyanophyta) is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes

from the color of the bacteria (Greek: κυανός (kyanós) = blue).

The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into

an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the

near-extinction of oxygen-intolerant organisms. According toendosymbiotic theory, chloroplasts in plants and

eukaryotic algae have evolved from cyanobacterial ancestors via endosymbiosis.

Contents

  [hide] 

1 Ecology

2 Characteristics

o 2.1 Nitrogen fixation

o 2.2 Ecology

3 Photosynthesis

o 3.1 Carbon fixation

o 3.2 Metabolism and Organelles

4 Relationship to chloroplasts

5 Relationship to Earth history

6 Classification

7 Biotechnology and applications

8 Health risks

9 See also

10 References

11 Further reading

12 External links

[edit]Ecology

A large bloom of cyanobacteria in Lake Atitlán

Cyanobacteria can be found in almost every conceivable environment, from oceans to fresh water to bare rock to soil. They can

occur as planktonic cells or form phototrophic biofilms in fresh water and marine environments, they occur in damp soil, or even

on temporarily moistened rocks in deserts. A few are endosymbionts in lichens, plants, various protists, orsponges and provide

energy for the host. Some live in the fur of sloths, providing a form of camouflage.

Aquatic cyanobacteria are probably best known for the extensive and highly visible blooms that can form in both freshwaterand

the marine environment and can have the appearance of blue-green paint or scum. The association of toxicity with such blooms

has frequently led to the closure of recreational waters when blooms are observed. Marine bacteriophages are a

significant parasite of unicellular marine cyanobacteria. When they infect cells, they lyse them, releasing more phages into the

water.[3]

[edit]Characteristics

[edit]Nitrogen fixation

Blue-green algae cultured in specific media. Blue-green algae can be helpful in agriculture as they have the capability to fix atmospheric

nitrogen to soil.

Cyanobacteria include unicellular and colonial species. Colonies may form filaments, sheets or even hollow balls. Some

filamentous colonies show the ability to differentiate into several different cell types: vegetative cells, the normal, photosynthetic

cells that are formed under favorable growing conditions; akinetes, the climate-resistant spores that may form when

environmental conditions become harsh; and thick-walled heterocysts, which contain the enzyme nitrogenase, vital for nitrogen

fixation. Heterocysts may also form under the appropriate environmental conditions (anoxic) when fixed nitrogen is scarce.

Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas

into ammonia (NH3), nitrites (NO−

2) or nitrates (NO−

3) which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not bioavailable to

plants).

Rice plantations utilize healthy populations of nitrogen-fixing cyanobacteria (Anabaena, as symbiotes of the aquatic fern Azolla)

for use as rice paddy fertilizer.[4]

Cyanobacteria are arguably the most successful group of microorganisms on earth. They are the most genetically diverse; they

occupy a broad range of habitats across all latitudes, widespread in freshwater, marine and terrestrial ecosystems, and they are

found in the most extreme niches such as hot springs, salt works, and hypersaline bays. Photoautotrophic, oxygen-producing

cyanobacteria created the conditions in the planet's early atmosphere that directed the evolution of aerobic metabolism and

eukarotic photosynthesis. Cyanobacteria fulfill vital ecological functions in the world's oceans, being important contributors to

global carbon and nitrogen budgets.

– Stewart and Falconer[5]

[edit]Ecology

Many cyanobacteria also form motile filaments, called hormogonia, that travel away from the main biomass to bud and form new

colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the

motile chain may be tapered. In order to break away from the parent colony, a hormogonium often must tear apart a weaker cell

in a filament, called a necridium.

Each individual cell of a cyanobacterium typically has a thick, gelatinous cell wall. They lack flagella, but hormogonia and some

species may move about by gliding along surfaces. Many of the multi-cellular filamentous forms of Oscillatoria are capable of a

waving motion; the filament oscillates back and forth. In water columns some cyanobacteria float by forming gas vesicles, like

in archaea. These vesicles are notorganelles as such. They are not bounded by lipid membranes but by a protein sheath.

Some of these organisms contribute significantly to global ecology and the oxygen cycle. The tiny marine

cyanobacterium Prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open

ocean.[6] Many cyanobacteria even display the circadian rhythms that were once thought to exist only in eukaryotic cells

(see bacterial circadian rhythms).

[edit]Photosynthesis

A cyanobacteria bloom near Fiji

Colonies of Nostoc pruniforme

[edit]Carbon fixation

Cyanobacteria account for 20–30%[citation needed] of Earth's photosynthetic productivity and convert solar energy into biomass-stored

chemical energy at the rate of ~450 TW. Cyanobacteria utilize the energy of sunlight to drive photosynthesis, a process where

the energy of light is used to split water molecules into oxygen, protons, and electrons. While most of the high-energy electrons

derived from water are utilized by the cyanobacterial cells for their own needs, a fraction of these electrons are donated to the

external environment via electrogenic activity.[7] Cyanobacterial electrogenic activity is an important microbiological conduit of

solar energy into the biosphere.

[edit]Metabolism and Organelles

Cyanobacteria have an elaborate and highly organized system of internal membranes which function in photosynthesis.

Cyanobacteria get their name from the bluish pigment phycocyanin, which they use to capture light for photosynthesis.

Photosynthesis in cyanobacteria generally uses water as an electron donor and producesoxygen as a by-product, though some

may also use hydrogen sulfide as occurs among other photosynthetic bacteria. Carbon dioxide is reduced to

form carbohydrates via the Calvin cycle. In most forms the photosynthetic machinery is embedded into folds of the cell

membrane, called thylakoids. The large amounts of oxygen in the atmosphere are considered to have been first created by the

activities of ancient cyanobacteria. Due to their ability to fix nitrogen in aerobic conditions they are often found as symbionts with

a number of other groups of organisms such as fungi (lichens), corals, pteridophytes (Azolla), angiosperms (Gunnera) etc.

Many cyanobacteria are able to reduce nitrogen and carbon dioxide under aerobic conditions, a fact that may be responsible for

their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity

of photosystem (PS) II and I (Z-scheme). In anaerobic conditions, they are also able to use only PS I — cyclic

photophosphorylation — with electron donors other than water (hydrogen sulfide, thiosulphate, or even molecular hydrogen[8])

just like purple photosynthetic bacteria. Furthermore, they share an archaeal property, the ability to reduce elemental sulfur

by anaerobic respiration in the dark. Their photosynthetic electron transport shares the same compartment as the components

of respiratory electron transport. Their plasma membrane contains only components of the respiratory chain, while

the thylakoid membrane hosts both respiratory and photosynthetic electron transport.

Attached to thylakoid membrane, phycobilisomes act as light harvesting antennae for the photosystems. The phycobilisome

components (phycobiliproteins) are responsible for the blue-green pigmentation of most cyanobacteria. The variations on this

theme are mainly due to carotenoids and phycoerythrins which give the cells the red-brownish coloration. In some

cyanobacteria, the color of light influences the composition of phycobilisomes. In green light, the cells accumulate more

phycoerythrin, whereas in red light they produce more phycocyanin. Thus the bacteria appear green in red light and red in green

light. This process is known as complementary chromatic adaptation and is a way for the cells to maximize the use of available

light for photosynthesis.

A few genera, however, lack phycobilisomes and have chlorophyll b instead (Prochloron, Prochlorococcus, Prochlorothrix).

These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several

different lines of cyanobacteria. For this reason they are now considered as part of the cyanobacterial group.

[edit]Relationship to chloroplasts

Gloeobacter

Prochlorococcus

Synechococcus

plastids

all other cyanobacteria

Cladogram showing plastids (chloroplasts

and similar) and basal cyanobacteria[9]

Chloroplasts found in eukaryotes (algae and plants) likely evolved from an endosymbiotic relation with cyanobacteria.

This endosymbiotic theory  is supported by various structural and genetic similarities[10] Primary chloroplasts are found among the

"true plants" or green plants – species ranging from sea lettuce to evergreens and flowerswhich contain chlorophyll b – as well

as among the red algae and glaucophytes, marine species which contain phycobilins. It now appears that these chloroplasts

probably had a single origin, in an ancestor of the clade called Primoplantae. Other algae likely took their chloroplasts from

these forms by secondary endosymbiosis or ingestion.

It was once thought that the mitochondria in eukaryotes also developed from an endosymbiotic relationship with cyanobacteria;

however, it is now suspected that this evolutionary event occurred when aerobic bacteria were engulfed by anaerobic host cells.

Mitochondria are believed to have originated not from cyanobacteria but from an ancestor of Rickettsia.[citation needed]

[edit]Relationship to Earth history

Stromatolites of fossilized oxygen-producing cyanobacteria have been found from 2.8 billion years ago, [11] possibly as old as 3.5

billion years ago.

Oncolites; Guilmette Formation (Late Devonian) near Hancock Summit, Pahranagat Range, Nevada

Stromatolites; (Proterozoic) Zebra River Canyon, Namibia

The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of

extant cyanobacteria. The geologic record indicates that this transforming event took place early in our planet's history, at least

2450-2320 million years ago (mya), and probably much earlier. Geobiological interpretation of Archean (>2500 mya)

sedimentary rocks remains a challenge; available evidence indicates that life existed 3500 mya, but the question of when

oxygenic photosynthesis evolved continues to engender debate and research.

A clear paleontological window on cyanobacterial evolution opened about 2000 mya, revealing an already diverse biota of blue-

greens. Cyanobacteria remained principal primary producers throughout the Proterozoic (2500-543 mya), in part because the

redox structure of the oceans favored photoautotrophs capable of nitrogen fixation.

The most common cyanobacterial structures in the fossil record are the mound-producing stromatolites and related oncolites.

Indeed, these fossil colonies are so common that paleobiology, micropaleontology and paleobotany cite the Pre-

Cambrian andCambrian period as an "age of stromatolites" and an "age of algae."

Green algae joined the blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only

with the Mesozoic era (251-65 mya) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in

marine shelf waters take modern form.

Today, the blue-green bacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of

biological nitrogen fixation, and—in modified form—as the plastids of marine algae.[12]

[edit]Classification

Tree of Life in Generelle Morphologie der Organismen (1866). Note the location of the genus Nostoc with algae and not with bacteria (kingdom

"Monera")

See also: Bacterial taxonomy

Historically, Bacteria were first classified as plants constituting the class Schizomycetes, which along with

the Schizophyceae (blue green algae/Cyanobacteria) formed the phylum Schizophyta.[13]then in the phylum Monera in the

kingdom Protista by Haeckel in 1866, comprising Protogens, Protamaeba, Vampyrella, Protomonae andVibrio, but

not Nostoc and other cyanobacteria, which were classified with algae[14] later reclassified as the Prokaryotes by Chatton.[15]

The cyanobacteria were traditionally classified by morphology into five sections, referred to by the numerals I-V. The first three

– Chroococcales, Pleurocapsales, andOscillatoriales – are not supported by phylogenetic studies. However, the latter two

– Nostocales and Stigonematales – are monophyletic, and make up the heterocystous cyanobacteria. The members of

Chroococales are unicellular and usually aggregate in colonies. The classic taxonomic criterion has been the cell morphology

and the plane of cell division. In Pleurocapsales, the cells have the ability to form internal spores (baeocytes). The rest of the

sections include filamentous species. In Oscillatoriales, the cells are uniseriately arranged and do not form specialized cells

(akinetes and heterocysts). In Nostocales and Stigonematales the cells have the ability to develop heterocysts in certain

conditions. Stigonematales, unlike Nostocales, includes species with truly branched trichomes. Most taxa included in the phylum

or division Cyanobacteria have not yet been validly published under the Bacteriological Code. Except:

The classes Chroobacteria, Hormogoneae and Gloeobacteria

The orders Chroococcales, Gloeobacterales, Nostocales, Oscillatoriales, Pleurocapsales and Stigonematales

The families Prochloraceae and Prochlorotrichaceae

The genera Halospirulina, Planktothricoides, Prochlorococcus, Prochloron, Prochlorothrix.

[edit]Biotechnology and applications

Spirulina tablets

The unicellular cyanobacterium Synechocystis sp. PCC6803 was the third prokaryote and first photosynthetic organism

whose genome was completely sequenced.[16] It continues to be an important model organism.[17] The smallest genomes have

been found in Prochlorococcus spp. (1.7 Mb)[18][19] and the largest in Nostoc punctiforme (9 Mb).[20] Those of Calothrix spp. are

estimated at 12–15 Mb,[21] as large as yeast.

Some cyanobacteria are sold as food, notably Aphanizomenon flos-aquae  and Arthrospira platensis (Spirulina).[22]

Recent research has suggested the potential application of cyanobacteria to the generation of Clean and Green Energy via

converting sunlight into electricity.[clarification needed]Currently efforts are underway to commercialize algae-based fuels such as diesel,

gasoline and jet fuel.[7][23][24]

[edit]Health risks

See also: Cyanotoxin

Some cyanobacteria produce toxins, called cyanotoxins. These include anatoxin-a, anatoxin-

as, aplysiatoxin, cylindrospermopsin, domoic acid, microcystin LR , nodularin R  (fromNodularia), or saxitoxin. Cyanobacteria

reproduce explosively under certain conditions. This results in algal blooms, which can become harmful to other species if the

cyanobacteria involved produce toxins.

These toxins can be neurotoxins, hepatotoxins, cytotoxins, and endotoxins, and can be toxic and dangerous to humans as well

as other animals and marine life in general. Several cases of human poisoning have been documented but a lack of knowledge

prevents an accurate assessment of the risks.[25][26][27] Recent studies suggest that significant exposure to high levels of some

species of cyanobacteria causes amyotrophic lateral sclerosis (ALS). The Lake Mascoma ALS cluster [28] and Gulf War veteran's

cluster are two notable examples.[26][27][29]

[edit]See also

Bacterial growthFrom Wikipedia, the free encyclopedia

Growth is shown as L = log(numbers) where numbers is the number of colony forming units per ml, versus T (time.)

Bacterial growth is the division of one bacterium into two daughter cells in a process called binary fission. Providing no

mutational event occurs the resulting daughter cells are genetically identical to the original cell. Hence, "local doubling" of the

bacterial population occurs. Both daughter cells from the division do not necessarily survive. However, if the number surviving

exceeds unity on average, the bacterial population undergoes exponential growth. The measurement of an exponential bacterial

growth curve in batch culture was traditionally a part of the training of all microbiologists; the basic means requires bacterial

enumeration (cell counting) by direct and individual (microscopic, flow cytometry[1]), direct and bulk (biomass), indirect and

individual (colony counting), or indirect and bulk (most probable number, turbidity, nutrient uptake) methods. Models reconcile

theory with the measurements.[2]

Contents

  [hide] 

1 Phases

2 See also

3 References

4 External links

Phases

Bacterial growth curve

In autecological studies, bacterial growth in batch culture can be modeled with four different phases: lag phase (A), exponential

or log phase (B), stationary phase(C), and death phase (D). IN the book "black" the bacterial growth phase classified 07

stages like-(A)lag phase (B)early log phase (C) log/exponential Phase (D)Early Stationery phase (E)stationary phase (f) Early

Death phase (G)Death phase..

1. During lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are

maturing and not yet able to divide. During the lag phase of the bacterial growth cycle, synthesis of RNA, enzymes and

other molecules occurs. So in this phase the microorganisms are not dormant.

2. Exponential phase (sometimes called the log phase or the logarithmic phase) is a period characterized by cell doubling.[3] The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited,

doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with

each consecutive time period. For this type of exponential growth, plotting the natural logarithm of cell number against

time produces a straight line. The slope of this line is the specific growth rate of the organism, which is a measure of

the number of divisions per cell per unit time.[3] The actual rate of this growth (i.e. the slope of the line in the figure)

depends upon the growth conditions, which affect the frequency of cell division events and the probability of both

daughter cells surviving. Under controlled conditions, cyanobacteria can double their population four times a day.[4]Exponential growth cannot continue indefinitely, however, because the medium is soon depleted of nutrients and

enriched with wastes.

3. During stationary phase, the growth rate slows as a result of nutrient depletion and accumulation of toxic products. This

phase is reached as the bacteria begin to exhaust the resources that are available to them. This phase is a constant

value as the rate of bacterial growth is equal to the rate of bacterial death.

4. At death phase, bacteria run out of nutrients and die.

This basic batch culture growth model draws out and emphasizes aspects of bacterial growth which may differ from the growth

of macrofauna. It emphasizes clonality, asexual binary division, the short development time relative to replication itself, the

seemingly low death rate, the need to move from a dormant state to a reproductive state or to condition the media, and finally,

the tendency of lab adapted strains to exhaust their nutrients.

In reality, even in batch culture, the four phases are not well defined. The cells do not reproduce in synchrony without explicit

and continual prompting (as in experiments with stalked bacteria [5]) and their exponential phase growth is often not ever a

constant rate, but instead a slowly decaying rate, a constant stochastic response to pressures both to reproduce and to go

dormant in the face of declining nutrient concentrations and increasing waste concentrations.

Batch culture is the most common laboratory growth method in which bacterial growth is studied, but it is only one of many. It is

ideally spatially unstructured and temporally structured. The bacterial culture is incubated in a closed vessel with a single batch

of medium. In some experimental regimes, some of the bacterial culture is periodically removed and added to fresh sterile

medium. In the extreme case, this leads to the continual renewal of the nutrients. This is a chemostat, also known as continuous

culture. It is ideally spatially unstructured and temporally unstructured, in a steady state defined by the rates of nutrient supply

and bacterial growth. In comparison to batch culture, bacteria are maintained in exponential growth phase, and the growth rate

of the bacteria is known. Related devices include turbidostats and auxostats.

Bacterial growth can be suppressed with bacteriostats, without necessarily killing the bacteria. In a synecological, true-to-nature

situation in which more than one bacterial species is present, the growth of microbes is more dynamic and continual.

Liquid is not the only laboratory environment for bacterial growth. Spatially structured environments such as biofilms

or agar surfaces present additional complex growth models.

See also