troph = nourishment

auto = self

chemo = chemical

chemoutotrophs

derive energy from chemical reactions

synthesize all necessary organic compounds from carbon dioxide

use inorganic energy sources, such as hydrogen sulfide, elemental sulfur, ferrous iron, molecular hydrogen, and ammonia

They can be also called as chemolithoautotrophs .

Most chemoautotrophs

are bacteria or archaea that live

in hostile environments such as deep

sea vents, active volcanoes and are

the primary producers in

such ecosystems

A unique characteristic of these

chemoautotrophic bacteria is that

they thrive at temperatures high

enough to kill other organisms

use inorganic reduced compounds as a

source of energy

This process is accomplished through

oxidation and ATP synthesis

Most chemolithotrophs are able to fix

carbon dioxide (CO2) through the Calvin

Cycle, a metabolic pathway in which

carbon enters as CO2 and leaves

as glucose

Chemolithotrophy: Energy from the Oxidation of Inorganic Electron Donors

8

Carry out respiration by coupling the

oxidation of an inorganic compound

to the reduction of membrane-bound

electron carriers:

most ATP produced by oxidative

phosphorylation

inorganic electron donor

protons pumped out

proton motive force

ATP synthesis

e– electron transport chain

sulfur oxidizers

nitrifying bacteria

iron oxidizers

Hydrogen oxidizers.

Anammox Bacteria

ATP has a free energy of -31.8

kJ/mol

2H2 + 02 2H20 (1)

2 H2 + C02 <CH20 > + H20 (2)

6H2 + 202 + CO2 <CH20> +5 H20 (3)

Hydrogen Bacteria

Ralstonia eutropha is a gram-negative soil bacterium of the

betaproteobacteria class

Many species of nitrifying bacteria

have complex internal membrane

systems that are the location for key

enzymes in nitrification: ammonia

monooxygenase which oxidizes

ammonia to hydroxylamine,

and nitrite oxidoreductase, which

oxidizes nitrite to nitrate.

Nitrifying bacteria are widespread in the

environment, and are found in highest

numbers where considerable amounts of

ammonia are present (areas with

extensive protein decomposition, and

sewage treatment plants).

They thrive in lakes and streams with high

inputs of sewage and wastewater

because of the high ammonia content.

Nitrification in nature is a two-step oxidation process of

ammonium (NH4+ or ammonia NH3) to nitrate (NO3

-)

catalyzed by two ubiquitous bacterial groups. The first

reaction is oxidation of ammonium to nitrite by

ammonium oxidizing bacteria (AOB) represented

by Nitrosomonas species. The second reaction is

oxidation of nitrite (NO2-) to nitrate by nitrite-oxidizing

bacteria (NOB), represented by Nitrobacter species.

Ammonia oxidation: It is a complex

process that requires several enzymes,

proteins and presence of oxygen. The

key enzymes, necessary to obtaining

energy during oxidation of ammonium

to nitrite are: ammonia

monooxygenase (AMO) and

hydroxylamine oxidoreductase (HAO)

In anoxic ammonia oxidation, the nitrifying bacteria can use ammonia

and nitrite as electron donors, a process called nitrification. The

ammonia-oxidizing bacteria produce nitrite.

Nitrite produced in first step autotrophic nitrification is oxidized to nitrate by nitrite oxidoreductase (N0R)(2). It is a membrane-associated iron-sulfur molybdoprotein, and is part of an electron transfer chain which channels electrons from nitrite to molecular oxygen. The molecular mechanism of oxidation nitrite is less described than oxidation ammonium.

The ammonia-oxidizing bacteria produce nitrite which is

then oxidized by the nitrite-oxidizing bacteria to nitrate.

Nitrosococcus

NH3

NO2–

Nitrobacter

NO2–

NO3–

No single bacterium oxidizes ammonia

all the way to nitrate.

Nitrobacter

Nitrobacter is a genus of mostly rod-shaped, gram-negative, and chemoautotrophic bacteria. Nitrobacter plays an important role in the nitrogen cycle by oxidizing nitrite into nitrate in soil

Nitrosomonas

Nitrosomonas is a genus comprising rod shaped chemoautotrophic bacteria. This bacteria oxidizes ammonia into nitrite as a metabolic process. Nitrosomonas are useful in treatment of industrial and sewage waste and in the process of bioremediation

“White Streamers”

color due to sulfur granules in cells

Fe Oxidation at low pH

The pH effect on Fe+2 concentrations is reflected in the energy yield:

Fe+2 + O2 + H+ Fe+3 + H2O

Thiobacillus ferrooxidans, an acidophilic iron-oxidizer, pH optimum for

growth of 2 to 3

Contribute to formation of acid mine drainage.

Thiobacillus-type [rods] in yellow

floc from acid water

The iron bacteria are chemolithotrophs that use ferrous iron (Fe2+) as

their sole energy source.

Most iron bacteria grow only at acid

pH and are often associated with

acid pollution from mineral and coal

mining.

Extensive development of

insoluble ferric hydroxide in a

small pool draining a bog in

Iceland. Iron deposits such as this

are widespread in cooler parts of

the world and are modern

counterparts of the extensive bog

iron deposits of earlier geological

eras

36

NH4+ + NO2

- N2 + 2 H2O

Anammox - Anaerobic ammonium oxidation

Brocadia anammoxidans

Brocadia anammoxidans

"Candidatus Brocadia anammoxidans" is a bacterial member of the

order Planctomycetes and therefore lacks peptidoglycan in its cell

wall, has a compartmentalized cytoplasm.

Anammox bacteria:

Planctomyces group

Enrichment culture of the anammox

bacterium Kuenenia stuttgartiensis

Eubacteria, known as "true bacteria," are prokaryotic

(lacking nucleus) cells that are very common in

human daily life.

They have a single strand of DNA. Eubacteria Lack a nuclear membrane. Eubacteria have phili which help transfer

DNA. The cytoplasm is filled with ribosomes. Eubacteria lack a nuclei or nucleus . Some Eubacteria have a flagella. A tail like

structure to help them move. Eubacteria have a plasma membrane to

hold the insides of the cell in place. They are enclosed by a cell wall that

provides as a rigid wall to keep the cells shape.

Phototrophic bacteria are a group of bacteria,

whose energy for growth is derived from sunlight

and their source of carbon comes from carbon

dioxide or organic carbon. There are two groups of

phototrophic bacteria, i.e., anoxygenic

phototrophic bacteria and oxygenic phototrophic

bacteria.

Cyanobacteria or blue-green bacteria

oxygenic photosynthesis

Purple bacteria anoxygenic photosynthesis

Green bacteria

anoxygenic photosynthesis

Cyanobacteria’s are photosynthetic bacterias,also referred as bluegreen algae.

Have similar chlorophyll a to the plants.

Oxygenic phototrophy(unique in evolution)

Nostoc

anabaena

Carry out anoxygenic photosynthesis; no O2 evolved

Morphologically diverse group

Genera fall within the Alpha-, Beta-, or

Gammaproteobacteria

Contain bacteriochlorophylls and carotenoid pigments

Produce intracytoplasmic photosynthetic membranes

with varying morphologies

- allow the bacteria to increase pigment content

- originate from invaginations of cytoplasmicmembrane

Liquid Cultures of Phototrophic Purple Bacteria

Rhodospirillum rubrum

Rhodobacter sphaeroides

Rhodopila globiformis

Purple Sulfur

BacteriaPurple Non-sulfur

Bacteria

› Use hydrogen sulfide (H2S) as an electron

donor for CO2 reduction in photosynthesis

› Sulfide oxidized to elemental sulfur (So) that

is stored as globules either inside or outside

cells

Sulfur later disappears as it is oxidized to

sulfate (SO42-)

› The family Chromatiaceae contains the purple-sulphur bacteria

Photomicrographs of Purple Sulfur Bacteria

Chromatium okenii Thiospirillum jenense

Thiopedia rosea Ectothiorhodospira mobilis

› Many can also use other reduced sulfur

compounds, such as thiosulfate (S2O32-)

› All are Gammaproteobacteria

› Found in illuminated anoxic zones of lakes and

other aquatic habitats where H2S accumulates,

as well as sulfur springs

Blooms of Purple Sulfur Bacteria

Lamprocystisroseopersicina

Algae (Spirogyra)

Chromatiumsp.

Thiocystis sp.

› Originally thought organisms were unable to use sulfide as an

electron donor for CO2 reduction, now know most can

› Most can grow aerobically in the dark as chemoorganotrophs

› Some can also grow anaerobically in the dark using

fermentative or anaerobic respiration

› Most can grow photoheterotrophically using light as an energy

source and organic compounds as a carbon source

› All in Alpha- and Betaproteobacteria

› The family Rhodospirillaceae contains the purple non-sulphur

bacteria

Phaeospirillum fulvum Rhodoblastus acidophilus

Rhodobacter sphaeoides

Green Non-Sulphur Bacteria

Green Sulfur Bacteria

GREEN SULFUR BACTERIA

These are obligatory phototrophic bacteria

Reproduction is from binary fission mode.

Photosynthesis is achieved using bacteriophyll c,d or e.

They use H2S as electron donor for CO2 fixation.

Granules of elemental sulphur are deposited only outside the cells and the sulphur can eventually be oxidized to SO4(-2).

. In this group of bacteria flexible filaments are formed and so these are also called as the green flexi bacteria. They possess gliding mobility. Most of them do not have gas vesicles. The organisms are mainly photoorganotrophic, as the purple non-sulphur bacteria, but they can also grow as photolithotrophs as the purple non-sulphur bacteria, but they can also grow as photolithotrophs with H2S as the electron donor. In the dark they can grow aerobically as chemoheterotrophs.