Aerobic anoxygenic phototrophs (AAPs) are photoheterotrophic prokaryotes that are widespread in many limnic and marine environments. So far, little is known about their distribution in peat-bog lakes. Seventeen peat-bog lakes were sampled during three summer seasons 2009, 2011, and 2012, and the vertical distribution of AAPs was determined by infrared epifluorescence microscopy. The analysis demonstrated that in the surface layers of the studied lakes, AAP abundance ranged from 0.3 to 12.04 × 10(5) cells mL(-1), which represents <1 to 18.3 % of the total bacteria. The vertical distribution of AAPs confirmed their presence in the upper parts of the water column with minimum numbers in the anoxic bottom waters. We have shown that the AAP abundance was significantly positively correlated with the water pH, and the highest proportion of photoheterotrophs was found in peat-bog lakes with a pH between 6.7 and 7.6. Our results demonstrated an influence of water acidity on the abundance of AAPs, which may reflect a fundamental difference in the microbial composition between acidic and pH neutral peat-bog lakes.

• Keywords
• Aerobic anoxygenic phototrophic bacteria, Environmental factors, Humic and dystrophic lakes, Peat-bog lakes, pH,
• MeSH
• Bacteria, Aerobic physiology   MeSH
• Lakes microbiology   MeSH
• Oxygen MeSH
• Water Microbiology MeSH
• Wetlands * MeSH
• Environmental Monitoring MeSH
• Soil * MeSH
• Seasons MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Oxygen MeSH
• Soil * MeSH

Magnesium-protoporphyrin IX monomethylester cyclase is one of the key enzymes of the bacteriochlorophyll biosynthesis pathway. There exist two fundamentally different forms of this enzyme. The oxygen-dependent form, encoded by the gene acsF, catalyzes the formation of the bacteriochlorophyll fifth ring using oxygen, whereas the oxygen-independent form encoded by the gene bchE utilizes an oxygen atom extracted from water. The presence of acsF and bchE genes was surveyed in various phototrophic Proteobacteria using the available genomic data and newly designed degenerated primers. It was found that while the majority of purple nonsulfur bacteria contained both forms of the cyclase, the purple sulfur bacteria contained only the oxygen-independent form. All tested species of aerobic anoxygenic phototrophs contained acsF genes, but some of them also retained the bchE gene. In contrast to bchE phylogeny, the acsF phylogeny was in good agreement with 16S inferred phylogeny. Moreover, the survey of the genome data documented that the acsF gene occupies a conserved position inside the photosynthesis gene cluster, whereas the bchE location in the genome varied largely between the species. This suggests that the oxygen-dependent cyclase was recruited by purple phototrophic bacteria very early during their evolution. The primary sequence and immunochemical similarity with its cyanobacterial counterparts suggests that acsF may have been acquired by Proteobacteria via horizontal gene transfer from cyanobacteria. The acquisition of the gene allowed purple nonsulfur phototrophic bacteria to proliferate in the mildly oxygenated conditions of the Proterozoic era.

• MeSH
• Bacterial Proteins analysis   chemistry   genetics   MeSH
• Photosynthesis genetics   MeSH
• Phylogeny MeSH
• Genome, Bacterial MeSH
• Oxygen metabolism   MeSH
• Oxygenases analysis   chemistry   genetics   MeSH
• Protein Isoforms analysis   chemistry   genetics   MeSH
• Proteobacteria enzymology   genetics   metabolism   MeSH
• Cyanobacteria enzymology   genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Oxygen MeSH
• magnesium protoporphyrin monomethyl ester oxidative cyclase MeSH Browser
• Oxygenases MeSH
• Protein Isoforms MeSH

Aerobic anoxygenic phototrophs contain photosynthetic reaction centers composed of bacteriochlorophyll. These organisms are photoheterotrophs, as they require organic carbon substrates for their growth whereas light-derived energy has only an auxiliary function. To establish the contribution of light energy to their metabolism, we grew the phototrophic strain Erythrobacter sp. NAP1 in a carbon-limited chemostat regimen on defined carbon sources (glutamate, pyruvate, acetate, and glucose) under conditions of different light intensities. When grown in a light-dark cycle, these bacteria accumulated 25% to 110% more biomass in terms of carbon than cultures grown in the dark. Cultures grown on glutamate accumulated the most biomass at moderate light intensities of 50 to 150 μmol m(-2) s(-1) but were inhibited at higher light intensities. In the case of pyruvate, we did not find any inhibition of growth by high irradiance. The extent of anaplerotic carbon fixation was detemined by radioactive bicarbonate incorporation assays. While the carboxylation activity provided 4% to 11% of the cellular carbon in the pyruvate-grown culture, in the glutamate-grown cells it provided only approximately 1% of the carbon. Additionally, we tested the effect of light on respiration and photosynthetic electron flow. With increasing light intensity, respiration decreased to approximately 25% of its dark value and was replaced by photophosphorylation. The additional energy from light allows the aerobic anoxygenic phototrophs to accumulate the supplied organic carbon which would otherwise be respired. The higher efficiency of organic carbon utilization may provide an important competitive advantage during growth under carbon-limited conditions.

• MeSH
• Aerobiosis MeSH
• Biomass MeSH
• Phototrophic Processes * MeSH
• Bicarbonates metabolism   MeSH
• Isotope Labeling MeSH
• Carbon Isotopes metabolism   MeSH
• Carbon Cycle MeSH
• Culture Media chemistry   MeSH
• Pyruvates metabolism   MeSH
• Sphingomonadaceae metabolism   radiation effects   MeSH
• Light * MeSH
• Darkness MeSH
• Electron Transport MeSH
• Carbon metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bicarbonates MeSH
• Carbon Isotopes MeSH
• Culture Media MeSH
• Pyruvates MeSH
• Carbon MeSH