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
 C & D are chlorins (1 reduced pyrrole
ring), others are bacteriochlorins (2
reduced rings)
 Chlorin – heterocyclic aromatic ring with 3
pyrroles at the center
 Photosynthetic pigment related to
chlorophyll

Chlorin
Bacteriochlorin: 2 reduced
pyrroles
Chlorin: 1 reduced pyrrole
Types
 Proteobacteria,
ie: purple bacteria
 Green sulfur bacteria
 Green non-sulfur bacteria
 Heliobacteria
Proteobacteria:
Purple Bacteria
• Gram 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
http://www.biol.tsukuba.ac.jp/~inouye/ino/bc/purple%20nonsulfur.html
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 nonsulfur
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 smokers @ 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
http://et.springer-ny.com:8080/prokPUB/chaprender/jsp/showchap.jsp?chapnum=304
Relatedness
 Determined from 16s rRNA
 Shows that they are more
closely related to nonphotosynthetic subgroups than
each other
Works Cited
Lindquist, John – Dept. of Bacteriology, U. of
Wisconsin - http://www.splammo.net/bact102/102pnsb.html
MicroBioNet -
http://www.microbionet.com.au/chromatiaceae.htm
The Prokaryotes –
Ed. Martin Dworkin, Department of
Microbiology, of Minnesota
http://et.springer-ny.com:8080/prokPUB/chaplist_organism_full.htm