A unique low light adaptation mechanism inRhodobacter azotoformans

The Growth-promoting Mechanism of Unusual Spectroscopic Form of LH2 (LH4) from Rhodopseudomonas palustris CGA009 in Low Light

The experimental evidence for the growth-promoting mechanism and the efficiency of energy transfer (EET) of LH4 under low light are still not available. To elucidate the light adaption mechanism of LH4, we deleted the genes pucBAd involved in the synthesis of the α/β polypeptides of LH4 in Rhodopseudomonas palustris CGA009. Compared to wild strain, the growth rate of pucBAd mutant significantly decreased under low light, while there were no significant changes in the growth rate, the contents and compositions of photopigments, absorption spectra of cell lysates under high light. Moreover, the fluorescence quantum efficiency (FQE) was used to further compare the EET between LH2 and LH4. The FQE in LH4 increased up to 1.5-fold than did in LH2. Collectively, this study showed that LH4 could provide more and high energetic state photons for promoting bacterial phototrophic growth in response to low-light environment.

Genome Sequence of Rhodoferax antarcticus ANT.BRT; A Psychrophilic Purple Nonsulfur Bacterium from an Antarctic Microbial Mat

Rhodoferax antarcticus is an Antarctic purple nonsulfur bacterium and the only characterized anoxygenic phototroph that grows best below 20 °C. We present here a high-quality draft genome of Rfx. antarcticus strain ANT.BR^T, isolated from an Antarctic microbial mat. The circular chromosome (3.8 Mbp) of Rfx. antarcticus has a 59.1% guanine + cytosine (GC) content and contains 4036 open reading frames. In addition, the bacterium contains a sizable plasmid (198.6 kbp, 48.4% GC with 226 open reading frames) that comprises about 5% of the total genetic content. Surprisingly, genes encoding light-harvesting complexes 1 and 3 (LH1 and LH3), but not light-harvesting complex 2 (LH2), were identified in the photosynthesis gene cluster of the Rfx. antarcticus genome, a feature that is unique among purple phototrophs. Consistent with physiological studies that showed a strong capacity for nitrogen fixation in Rfx. antarcticus, a nitrogen fixation gene cluster encoding a molybdenum-type nitrogenase was present, but no alternative nitrogenases were identified despite the cold-active phenotype of this phototroph. Genes encoding two forms of ribulose 1,5-bisphosphate carboxylase/oxygenase were present in the Rfx. antarcticus genome, a feature that likely provides autotrophic flexibility under varying environmental conditions. Lastly, genes for assembly of both type IV pili and flagella are present, with the latter showing an unusual degree of clustering. This report represents the first genomic analysis of a psychrophilic anoxygenic phototroph and provides a glimpse of the genetic basis for maintaining a phototrophic lifestyle in a permanently cold, yet highly variable, environment.

Acclimation strategy of Rhodopseudomonas palustris to high light irradiance

The ability of Rhodopseudomonas palustris cells to rapidly acclimate to high light irradiance is an essential issue when cells are grown under sunlight. The aim of this study was to investigate the photo-acclimation process in Rhodopseudomonas palustris 42OL under different culturing conditions: (i) anaerobic (AnG), (ii) aerobic (AG), and (iii) under H₂-producing (HP) conditions both at low (LL) and high light (HL) irradiances. The results obtained clearly showed that the photosynthetic unit was significantly affected by the light irradiance at which Rp. palustris 42OL was grown. The synthesis of carotenoids was affected by both illumination and culturing conditions. At LL, lycopene was the main carotenoid synthetized under all conditions tested, while at HL under HP conditions, it resulted the predominant carotenoid. Oppositely, under AnG and AG at HL, rhodovibrin was the major carotenoid detected. The increase in light intensity produced a deeper variation in light-harvesting complexes (LHC) ratio. These findings are important for understanding the ecological distribution of PNSB in natural environments, mostly characterized by high light intensities, and for its growth outdoors.

Powered by light: Phototrophy and photosynthesis in prokaryotes and its evolution

Photosynthesis is a complex metabolic process enabling photosynthetic organisms to use solar energy for the reduction of carbon dioxide into biomass. This ancient pathway has revolutionized life on Earth. The most important event was the development of oxygenic photosynthesis. It had a tremendous impact on the Earth's geochemistry and the evolution of living beings, as the rise of atmospheric molecular oxygen enabled the development of a highly efficient aerobic metabolism, which later led to the evolution of complex multicellular organisms. The mechanism of photosynthesis has been the subject of intensive research and a great body of data has been accumulated. However, the evolution of this process is not fully understood, and the development of photosynthesis in prokaryota in particular remains an unresolved question. This review is devoted to the occurrence and main features of phototrophy and photosynthesis in prokaryotes. Hypotheses concerning the origin and spread of photosynthetic traits in bacteria are also discussed.