Chapter3 Microbial nutrition

1.Nutrient requirement

2.Nutritional types of microorganisms

3.Uptake of nutrients

4.Culture media

Microbial Growth Conditions1. Macronutrients

2. Micronutrients

3. Growth factors

4. Environmental factors: temperature; pH; Oxygen et al.

Microorganisms require about ten elements in large quantities, because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. Several other elements are needed in very small amounts and are parts of enzymes and cofactors.

Nutrient requirements

Microbial Nutrition

1. Macronutrients: required in large amounts, including: carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus (Components of carbonhydrates, lipids, proteins, and mucleic acids ); potass

ium, calcium, magnesium and iron (cations and part of enzymes and cofactors).

2. Micronutrients: Microbes require very small amounts of other mineral elements, such as iron, copper, molybdenum, and zinc; these are referred to as trace elements. Most are essential for activity of certain enzymes, usually as cofactors.

Nutrients: Substances in the environment used by organisms for catabolism and anabolism.

contaminants in water, glassware, and regular media components often are adequate for growth.

Growth Factors

Amino acids are needed for protein synthesis,

purines and pyrimidines for nucleic acid synthesis.

Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth.

(1)amino acids, (2) purines and pyrimidines, (3) vitamins

Requirement for carbon, hydrogen and oxygen

Carbon sources: heterotrophs: “CHO” autotrophs: CO2

Extraordinary flexibility: No naturally occurring organic molecule cannot be used by some microorganism. eg. Paraffin, rubber.Omnivores: use over 100 different carbon compounds.Fastidious: catabolize only a few carbon compound Relatively indigestible human-made substances are metabolized by complex populations of microorganisms.

Major nutritional type

Sources of energy,

hydrogen/electrons,

and carbon

Representative microorganisms

Photoautotroph

(Photolithotroph)

Light energy, inorganic hydrogen/electron(H/e-) donor, CO2 carbon source

Algae, Purple and green bacteria, Cyanobacteria

Photoheterotroph

(Photoorganotroph)

Light energy, inorganic H/e- donor,

Organic carbon source

Purple nonsulfur bacteria,

Green sulfur bacteria

Chemoautotroph

(Chemolithotroph)

Chemical energy source (inorganic), Inorganic H/e- donor, CO2 carbon source

Sulfur-oxdizing bacteria, Hydrogen bacteria,

Nitrifying bacteria

Chemoheterotroph

(Chenoorganotroph)

Chemical energy source (organic), Organic H/e- donor, Organic carbon source

Most bacteria, fungi, protozoa

Nutritional types of microorganisms

Algae, Cyanobacteria

CO2 + H2O Light + Chlorophyll

（ CH2O ） +O2

Purple and green bacteria

CO2 + 2H2S Light + bacteriochlorophyll

（ CH2O ） + H2

O + 2S

Purple nonsulfur bacteria (Rhodospirillum)

CO2 + 2CH3CHOHCH3 Light + bacteriochlorophyll （ CH2O ）

+ H2O + 2CH3COCH3

Photoautotroph:

Photoheterotroph:

Property cyanobacteria Green and purple bacteria

Purple nonsulfur bacteria

Photo - pigment Chlorophyll Bcteriochlorophyll Bcteriochlorophyll

O2 production Yes No No

Electron donors H2O H2, H2S, S H2, H2S, S

Carbon source CO2 CO2 Organic / CO2

Primary products

of energy conversion

ATP + NADPH ATP ATP

Properties of microbial photosynthetic systems

Chemoautotroph:

Nitrifying bacteria

2 NH4+ + 3 O2 2 NO2- + 2 H2O + 4 H+ + 132 Kcal

Bacteria Electron donor

Electron acceptor

Products

Alcaligens and Pseudomonas sp.

H2 O2 H2O

Nitrobacter NO2- O2 NO3

- , H2ONitrosomonas NH4

+ O2 NO2- , H2O

Desulfovibrio H2 SO4 2- H2O. H2S

Thiobacillus denitrificans S0. H2S NO3- SO4

2- , N2

Thiobacillus ferrooxidans Fe2+ O2 Fe3+ , H2O

Nutritional types of microorganisms

• Phototrophs: use light as energy source.• Chenotrophs: obtain energy from the oxida

tion of chemical compounds.• Lithotrophs: use reduced inorganic substan

ces as their electron source.• Organotrophs: exteact electrons from orga

nic compounds.

Mixotrophic: many purple nonsulfur bacteria

1. No oxygen: photoorganotrophic heterotrophs

2. Normal oxygen: oxidize organic molecules and function chemotrophically.

3. Low oxygen: photosynthesis and oxidative metabolism

Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion and must be transported by one of three major mechanisms involving the use of membrane carrier proteins.

Uptake of nutrients

1, Phagocytosis – Protozoa

2, Permeability absorption – Most microorganisms

• passive transport (simple diffusion)

• facilitated diffusion

• active transport

• group translocation

A few substances, such as glycerol, H2O, O2

can cross the plasma membrane by passive diffusion. Passive diffusion is the process in which molecules move from a region of higher concentration to one of lower concentration as a result of random thermal agitation.

no carrier protein;

no energy.

passive diffusion

The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the plasina membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion.

Facilitated diffusion

The rate of facilitated diffusion increases with the concentratioti gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion.

Facilitated diffusion

• higer con. lower con.

• Facilitated diffusion: carrier protein, permeases.

• Each carrier is selective and will transport only closely related solutes.

Seem not to be important in procaryotes, much more prominent in Eucaryotic cells.

The membrane carrier can change conformation after binding an external molecule and subsequently release the molecule on the cell interior. It then returns to the outward oriented position and is ready to bind another solute molecule.

A model of facilitated diffusion

Because there is no energy input, molecules will continue to enter only as long as their concentration is greater on the outside.

Active transport is the transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input.

•lower con. higer con.

•Permeases, energy

Active transport

Proton gradients• Symport: linked transport of

two substances in the same direction.

• Antiport: linked transport of two substances in the opposite direction.

• Uniport: one substance enter

A process in which a molecule is transported into the cell while being chemically altered.

The best-known group translocation system is the phosphoenolpyruvate: sugar phosphotransferase system (PTS), which transports a variety of sugars into procaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor.

Group translocationGroup translocation

PTS: sugar phosphortransferase system

PEP+sugar(outside)pyruvate+sugar-P(inside)

The following components are involved in the system:

phosphoenolpyruvate, PEP;

EI (enzyme I), Hpr (the low molecular weight heat-stable protein): cytoplasmic, common to all PTSs.

EII (enzyme II) : EIIa: cytoplasmic and soluble

EIIb: hydrophilic but frequently is attached toEIIc. EIIc: a hydrophobic protein that is embedded in the

membrane. Only specific sugars and varies with PTS.

The phosphoenolpyruvate: sugar phosphotransferase system of E. coli.

Items Passive diffusion

Facilitated diffusion

Active transport

Group translocation

carrier proteins Non Yes Yes Yes

transport speed Slow Rapid Rapid Rapid

against gradient Non Non Yes Yes

transport molecules

No specificity Specificity Specificity Specificity

metabolic energy

No need Need Need Need

Solutes molecules

Not changed Changed Changed Changed

Simple comparison of transport systems

Iron uptake• Cytochromes and many enzymes• Extreme insolubility of ferric iron(Fe3+) and its derivatives.

Difficult• Siderophores: low M.W., be able to complex with ferric ir

on and supply it to the cell.• Microorganisms secrete siderophores when little iron is av

ailable in the medium. iron-siderophore complex bind the receptor of cell surface:

Fe3+ release; complex enter by ABC transporter.

Siderophores (S)Siderophores (S)

Fe Fe 2+2+//SS

ReceptorReceptor

Fe Fe 2+2+//SS

Cuture media A culture media is a solid or liquid preparation used to grow, transport, and store microorganisms.

Other functions: Isolation and identification The testing of antibiotic sensitivities Water and food analysis Industrial microbiology, et. al

Synthetic or defined media

• A medium in which all components are known.

eg. Medium for E.coli (g/liter)

glucose 1.0; Na2HPO4 16.4; KH2PO4 1.5; (NH4)2SO4 2.0; MgSO4 · 7H2O 200mg; CaCl2 10mg; FeSO4 · 7H2O 0.5mg; Final pH 6.8-7.0

Complex media

• Media that contain some ingredients of unknown chemical composition like peptones, meat extract, and yeast extract.

• What is peptones? Protein hydrolysateseg. LB medium: peptone; yeast extract; s

odium chloride; glucose.

Solid medium

• Liquid media+1.0-2.2% agar, common 1.5%.

• What is agar? Agar is a sulfated polymer composed mainly of D-galactose, 3,6-anhydro-L-galactose, and D-glucurouic acid, extracted from red algae.

40-42 harden℃ 80-90 melt℃• Most microorganism cannot degrade it.

• Other: silica gel for autotrophic bacteria

Types of media

• Selective media: favor the growth of particular microorganisms.

“ 加抑” : add componments which inhibite the growth of unfavored bacteria.

“ 加富” : add components which promote the growth of favored bacteria.

• Differential media: distinguish between different groups of bacteria.

MacConkey agar: lactose, neutral red dye; lactose-fermenting colonies appear pink to red in color.

What we have learned so far?

• Macro- and micronutrients? Defined medium and complex medium?

• Requirements for carbon, hydrogen,oxygen, nitrogen, phosphorus and sulfur?

• Nutritional types of microorganisms• What are growth factors?• What are facilitated diffusion, Active transport. G

roup translocation, endocytosis and their difference?

• How do cell uptake iron?• How to prepare a medium for cultivation microor

ganisms?