Bacteria Fundamentals: Photosynthesis, Nitrogen Fixation and Metabolism
Phototrophic and Anoxygenic Bacteria
The FS antenna complex in the present and the Bacteriochlorophyll (BChl) and sulfur-containing (BVA) phototrophic bacteria and anoxygenic algae are the main focus. The chlorosomes consist primarily of bacteriochlorophyll. Different antenna complexes from the FS-complexes have a large matrix of pigments and proteins.
Oxygenic Cyanobacteria (Oxygenic Algae)
- O2 formation contributed to the Earth's atmosphere.
- Bacteria are very diverse and have broad habitats.
- FS-mats are diverse, either immobile or mobile through gliding motility.
- Algae produce toxins.
- Algae present cyanophycin.
- Specialized cells: heterocysts and akinetes.
- They do not have phycobiliproteins as antenna pigments.
Heterocysts fix atmospheric N2 through the enzyme nitrogenase, which requires photosystem I.
Supramolecular structures, in the form of cylinders or rods, are attached to the surface of the thylakoid membrane in cyanobacteria, giving a granular appearance. This is similar to what is seen in reproductive cells of cyanobacteria.
Prochlorophytes
Prochlorophytes possess chlorophyll b, while cyanobacteria do not. Prochlorophytes can live endosymbiotically within free-living or eukaryotic cells.
Morphology and Reproduction
Filaments are straight, and the salient central region and extremes overlap. Generally strict aerobic or anaerobic facultative bacteria; some can ferment carbohydrates.
Budding bacteria reproduce by formation of a bud at one end of the cell or by a hyphal extension.
Extension of the cell wall and cytoplasmic membrane occurs in Verrucomicrobia and Planctomycetes.
The peduncle (stalk) appendage cannot live without cytoplasm, and it is prokaryotic.
Methylotrophs and Nitrifying Bacteria
When the source of energy and carbon is methane, methylamine, or other compounds, they reduce C-atoms under aerobic conditions. Methylotrophs can make their own organic compounds.
Nitrifiers fix nitrogen from the environment. Nitrifying bacteria include both ammonia oxidizers (Nitrosomonas, called nitrosifiers) and nitrite oxidizers (Nitrobacter), collectively called nitrifiers.
They are photoautotrophic and chemolithotrophic.
Iron and Manganese Bacteria
A hollow tube surrounds the cell, which can contain oxidized Fe or manganese. Through cooperation with cells on solid surfaces, they obtain solids and nutrients. Examples include Sphaerotilus and Leptothrix, which belong to the Betaproteobacteria, order Burkholderiales.
Sulfur-Oxidizing Bacteria
Some bacteria (chemolithotrophs) oxidize H2S. Sulfur oxidation is an essential process. Sulfur-oxidizing algae contribute to the success of rice cultivation. Their activity with deep-zone invertebrates depends on geochemical mixing and is the primary productivity of these areas with bacteria. They are used in biodesulfurization to remove toxic and corrosive sulfur compounds.
In sulfur springs, decomposing algae, mud, and contaminated water, sulfur-oxidizing bacteria live in areas with little or no O2. They are aerobic, require O2, and the source of carbon is CO2. They are chemolithoautotrophs and use aerobic respiration.
Methylotrophs and Symbiosis
Some organisms are obligate methylotrophs (compounds with a single carbon, such as methanol, formaldehyde). They are found in sediments where these compounds are not present. They are not found in symbiosis within the digestive systems of marine organisms.
They oxidize organic compounds with one carbon atom and transform them via methane decomposition into new material in anaerobic cells.
Enteric and Vibrio Bacteria
Vibrionaceae are bacteria with polar or lateral flagella, are oxidase positive, bioluminescent, and accumulate poly-β-hydroxybutyrate. Many are aquatic organisms and pathogens. Enterobacteriaceae (representatives include Escherichia and Salmonella) are intestinal tract inhabitants that produce gas from glucose and ferment disaccharides.
Chemolithoautotrophs use CO2 or acetate as the carbon source, while the electron donor is H2S or H2. They have the ability to oxidize sulfur and are anoxygenic phototrophs (no O2 production).
Luciferase and Quorum Sensing
Luciferase is regulated by accumulation of an autoinducer (quorum sensing). It is based on a deviation in respiratory metabolism: in the presence of O2, reduced flavin mononucleotide (FMNH2) is not used by luciferase, which leads to excitation. FMNH2 must recover to its normal state to emit light.
Mixed Acid and Butanediol Fermentation
Mixed acid fermentation gives rise to acetic, formic, succinic acids and ethanol. These are independent pathways whose functioning varies with the quantities of final products. Some bacteria produce 2,3-butanediol through a separate pathway.
Indicators and Applications
Some bacteria serve as indicators of contamination, forming part of the analysis of microbiological water quality.
Photosynthetic Pigments and Pathogens
Anoxygenic VRDS bacteria with FS contain bacteriochlorophyll a, b, g as pigments, and bacteriochlorophyll c, d, e as antenna pigments.
Examples of pathogenic Vibrio species are Vibrio cholerae, Vibrio vulnificus, and Vibrio parahaemolyticus. Some microbes control P and act as predators.
Sulfate and Sulfur Reduction
Dissimilatory sulfate-reducing bacteria use organic acids, glycerol, or H2 as electron donors (energy source) to reduce SO42- to H2S + H2O (ATP synthesis). Sulfur-reducing bacteria use acetate or ethanol as electron donors to reduce S0 to H2S.
Reproduction and Growth
Binary fission is the asexual form of reproduction in protozoa, algae, and bacteria. Budding (asymmetric division or bud formation) occurs as cells grow and develop, and may produce separate offspring or attached colonies.
Distribution and Ecology
Bacteria have a wide distribution in water and facultative soils. Many are Gram-negative predators or parasites.
Taxonomy of Caulobacter
Domain: Bacteria; Phylum: Proteobacteria; Class: Alphaproteobacteria; Order: Caulobacterales; Family: Caulobacteraceae; Genus: Caulobacter.
Metabolic Cycles and pH
The reverse tricarboxylic acid cycle occurs in anaerobic habitats. An acidic pH is required for Betaproteobacteria that are chemolithoautotrophs oxidizing sulfur.
Respiration Types
Aerobic respiration uses O2 as the terminal electron acceptor. When NO3- is used as the terminal electron acceptor, anaerobic respiration occurs, producing reduced nitrogen products; these are denitrifiers. Chemolithoautotrophs are aerobic.
Trichomes and Epibionts
Some trichomes form filaments that bind substrate with mucilage and attach to mollusks. Epibionts require oxygen and, in many cases, light.
Inorganic Compounds
Inorganic compounds serve as electron sources, and chemical compounds are oxidized to produce energy. These organisms are heterotrophic or autotrophic depending on their carbon source.