Aerobic anoxygenic phototrophs (AAPs) represent a relatively recently discovered unique BChl a-containing bacterial community. These organisms own a fully functional bacterial photosynthetic system. Their photosynthesis is operative only in the presence of oxygen. However, they are not able to grow autotrophically, they require a source of organic carbon for growth and metabolism. I have characterized the photosynthetic apparatus of Erythrobacter sp. NAP1, Roseobacter sp. COL2P and the strains Dor-2m, Dor-vul and Zun-kholbo. BChl a performs the function of the main light-harvesting pigment. Spheroidenone is the major carotenoid of the strains COL2P, Dor-2m, Dor-vul and Zun-kholbo. The NAP1 strain contains "non-photosynthetic" erythroxanthin sulfate, which is bound neither to the reaction center nor to the light-harvesting complex. Bacteriorubixanthinal, zeaxanthin and erythroxanthin are the main photosynthetic carotenoids of NAP1, coupled to the light- harvesting system. This system is composed of inner LH1 complex and reaction center, with no peripheral LH2 complexes. The photosynthetic unit size, in comparison with a typical anaerobic phototroph Rhodobacter sphaeroides, is limited due to the absence of LH2 antenna. The purified LH1-RC complex isolated from NAP1 is relatively thermostable,...

This thesis is concerned with designing specific primers for the gene bchY of chlorophyllid reductase from biosynthetic pathway of bacteriochlorophyll a and using this gene as a molecular marker for detection of aerobic anoxygenic phototrophs. The phylogenetic analyses based on gene bchY was done from selected AAP isolates and natural microbial communities in lakes in the Tyrolian Alps.

The current research project investigated the anoxygenic phototrophic and metal(loid) transforming bacteria of hypersaline and deep ocean hydrothermal environments. The East German Creek brine springs, an unusual flowing hypersaline system, was enumerated using classical techniques. Subterranean sulfide supported purple sulfur and nonsulfur bacteria, but at the highly oxygenated surface, aerobic anoxygenic phototrophs (AAP) were numerically dominant (up to 16-36% of cultivable bacteria). Strains (EG8, EG13, EG17, EG19) with unusual phylogenetic affiliation and novel photosynthetic and metal(loid) reducing traits were described taxonomically. Chromocurvus halotolerans gen. nov., sp. nov. was proposed as a second example of a gammaproteobacterial AAP. It exhibited bent rod-shaped cells, unusual among AAP. Facultatively anaerobic Charonomicrobium ambiphototrophicum gen. nov., sp. nov. was capable of both aerobic and anaerobic anoxygenic photosynthesis, and incapable of photoautotrophy, distinguishing it from both AAP and purple nonsulfur bacteria. Roseovarius vanadiphilum sp. nov. surprisingly produced 4.5 times more biomass and 2 times more bacteriochlorophyll (BChl) at extremely high NaVO3 concentration (7.5 g/l) than in metal-free medium. A second novel metabolic mode, anaerobic respiration on the toxic metalloid tellurate, was described for a relative of non-phototrophic Shewanella frigidimarina (ER-Te-48), from deep ocean hydrothermal vent Paralvinella worms at Explorer Ridge in the Pacific Ocean. Other strains respired on SeO32- (ER-Se-17L), VO3- (ER-V-6), and VO43- (AV-V-25). These organisms provided the first examples of anaerobic respiration on Te, Se and V at hydrothermal vents. High level resistance of AAP to metal(loid)s prompted investigation of the influence of TeO32- on photosynthetic pigment production in species including Erythromicrobium ramosum (from a terrestrial hydrothermal system) and Erythrobacter litoralis (from a hypersaline supralittoral system). Tellurite enhanced photosynthetic pigment production up to 3.4 times, consistent with an antioxidant carotenoid-based defense mechanism. However, in E. litoralis BChl precursors such as Mg protoporphyrin or its monomethyl ester also accumulated, indicating biosynthetic pathway interruption. In hydrothermal and hypersaline ecosystems, largely devoid of eukaryotic phototrophs but often enriched in metal(loid)s, AAP and metal(loid) reducers are key modulators of nutrient and toxin availability. The presented results on their ecology, physiology and biochemistry have important implications for theoretical understanding of extreme environments and hold potential for biotechnological applications.

The current research project investigated the anoxygenic phototrophic and metal(loid) transforming bacteria of hypersaline and deep ocean hydrothermal environments. The East German Creek brine springs, an unusual flowing hypersaline system, was enumerated using classical techniques. Subterranean sulfide supported purple sulfur and nonsulfur bacteria, but at the highly oxygenated surface, aerobic anoxygenic phototrophs (AAP) were numerically dominant (up to 16-36% of cultivable bacteria). Strains (EG8, EG13, EG17, EG19) with unusual phylogenetic affiliation and novel photosynthetic and metal(loid) reducing traits were described taxonomically. Chromocurvus halotolerans gen. nov., sp. nov. was proposed as a second example of a gammaproteobacterial AAP. It exhibited bent rod-shaped cells, unusual among AAP. Facultatively anaerobic Charonomicrobium ambiphototrophicum gen. nov., sp. nov. was capable of both aerobic and anaerobic anoxygenic photosynthesis, and incapable of photoautotrophy, distinguishing it from both AAP and purple nonsulfur bacteria. Roseovarius vanadiphilum sp. nov. surprisingly produced 4.5 times more biomass and 2 times more bacteriochlorophyll (BChl) at extremely high NaVO3 concentration (7.5 g/l) than in metal-free medium. A second novel metabolic mode, anaerobic respiration on the toxic metalloid tellurate, was described for a relative of non-phototrophic Shewanella frigidimarina (ER-Te-48), from deep ocean hydrothermal vent Paralvinella worms at Explorer Ridge in the Pacific Ocean. Other strains respired on SeO32- (ER-Se-17L), VO3- (ER-V-6), and VO43- (AV-V-25). These organisms provided the first examples of anaerobic respiration on Te, Se and V at hydrothermal vents. High level resistance of AAP to metal(loid)s prompted investigation of the influence of TeO32- on photosynthetic pigment production in species including Erythromicrobium ramosum (from a terrestrial hydrothermal system) and Erythrobacter litoralis (from a hypersaline supralittoral system). Tellurite enhanced photosynthetic pigment production up to 3.4 times, consistent with an antioxidant carotenoid-based defense mechanism. However, in E. litoralis BChl precursors such as Mg protoporphyrin or its monomethyl ester also accumulated, indicating biosynthetic pathway interruption. In hydrothermal and hypersaline ecosystems, largely devoid of eukaryotic phototrophs but often enriched in metal(loid)s, AAP and metal(loid) reducers are key modulators of nutrient and toxin availability. The presented results on their ecology, physiology and biochemistry have important implications for theoretical understanding of extreme environments and hold potential for biotechnological applications.