Anoxygenic Phototrophs

What are they?  Photosynthetic bacteria which use a reducing agent and light energy to build organic material, but do not produce oxygen  Use bacteriochlorophyll to accomplish photosynthesis – specific to each type of bacteria  Starch (carbohydrate) is a main product

Bacteriochlorophyll 6 types: a,b,c,d,e,g 6 types: a,b,c,d,e,g C & D are chlorins (1 reduced pyrrole ring), others are bacteriochlorins (2 reduced rings) C & D are chlorins (1 reduced pyrrole ring), others are bacteriochlorins (2 reduced rings) Chlorin – heterocyclic aromatic ring with 3 pyrroles at the center Chlorin – heterocyclic aromatic ring with 3 pyrroles at the center Photosynthetic pigment related to chlorophyll Photosynthetic pigment related to chlorophyll

Chlorin Chlorin: 1 reduced pyrrole Bacteriochlorin: 2 reduced pyrroles

Types  Proteobacteria, ie: purple bacteria  Green sulfur bacteria  Green non-sulfur bacteria  Heliobacteria

Proteobacteria: Purple Bacteria Gram negative, non-sporing, non acid fast, varying morphologiesGram negative, non-sporing, non acid fast, varying morphologies  Pigmented with bacteriochlorophyll a or b & carotenoids (organic pigments)  Anoxygenic type II photosynthesis in rxn centers on cell membranes  Reducing agent is sulfur or hydrogen  CO2 + 2H2S  CH2O + H2O + 2S

Purple Sulfur Bacteria - Chromatiaceae Electron sources: Example: Gamma type Red/purple pigmentation from carotenoids

Purple Non-sulfur Bacteria Rhodospirillaceae  Alpha type  Photoorganoheterotroph  Use organic e- donors, simple organic molecules (instead of CO2), and light energy for metabolism  Genus Magnetospirillum contain tiny chains of magnetite  Allow them to sense the Earth’s magnetic field and orient themselves

Rhosospirillum Rhodopseudomonas

Green Non-sulfur Bacteria  Chloroflexus is major representative  Filamentous, gliding, and thermophilic  Isolated from neutral to alkaline hot springs  Resembles green sulfur bacteria in ultrastructure and photosynthetic pigment  Metabolism similar to that of purple non- sulfur

Green Sulfur Bacteria  Have their own phylum: Chlorobi  Non-motile, except for one species  Can be baccilus, coccus, or spiralus  Environment must be free of oxygen  Use bacteriochlorophyll c,d,& e in chlorosome vesicles on cell membrane  Sulfide is reducing agent  Found in black 2500 ft.

Heliobacteria  Use bacteriochlorophyll g on cell membrane  Gram negative, endospore forming, obligate anaerobes  Common in dry environments, soil  Strong N-fixation  possible symbiotic relationship with plants

Heliobacterium chlorum Heliobacterium modesticaldum

Relatedness  Determined from 16s rRNA  Shows that they are more closely related to non- photosynthetic subgroups than each other

Works Cited Lindquist, John – Dept. of Bacteriology, U. of Wisconsin - MicroBioNet - The Prokaryotes – Ed. Martin Dworkin, Department of Microbiology, of Minnesota