Microbiology of Nitrogen Fixation by Anoxygenic Photosynthetic Bacteria

In order to reduce the protein content of wastewater, photosynthetic bacteria producing proteinases were screened from wastewater of various sources and stocked in culture. An isolated strain, KDDS1, was identified as Rubrivivax gelatinosus, a purple nonsulfur bacterium that secretes proteinase under micro-aerobic conditions under light at 35 C. Molecular weight of the purified enzyme was estimated to be 32.5 kDa. The enzyme showed the highest activity at 45 C and pH 9.6, and the activity was completely inhibited by phenylmethyl sulfonyl fluoride (PMSF), but not by EDTA. The amino-terminal 24 amino acid sequence of the enzyme showed about 50% identity to those of serine proteinases from Pseudoalteromonas piscicida strain O-7 and Burkholderia pseudomallei. Thus, the enzyme from Rvi. gelatinosus KDDS1 was thought to be a serine-type proteinase. This was the first serine proteinase characterized from photosynthetic bacteria.

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“…10) Rvi. gelatinosus is found not only to be able to fix nitrogen, 11,12) but also to liquefy gelatin.…”

Section: Resultsmentioning

confidence: 99%

Purification and Characterization of Alkaline Serine Proteinase from Photosynthetic Bacterium,Rubrivivax gelatinosusKDDS1

Oda

Tanskul

Oyama

et al. 2004

Bioscience, Biotechnology, and Biochemistry

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“…H. modesticaldum is an active dinitrogen fixer, and this species and the green sulfur bacterium Chlorobaculum tepidum are the only cultured anoxygenic phototrophs that are capable of N 2 fixation at temperatures above 50°C (23,31). The organization of the nif regulon in H. modesticaldum is identical to that in Heliobacterium chlorum (15).…”

Section: Genome Properties H Modesticaldum Strain Ice1mentioning

confidence: 91%

The Genome of Heliobacterium modesticaldum , a Phototrophic Representative of the Firmicutes Containing the Simplest Photosynthetic Apparatus

et al. 2008

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Despite the fact that heliobacteria are the only phototrophic representatives of the bacterial phylum Firmicutes, genomic analyses of these organisms have yet to be reported. Here we describe the complete sequence and analysis of the genome of Heliobacterium modesticaldum, a thermophilic species belonging to this unique group of phototrophs. The genome is a single 3.1-Mb circular chromosome containing 3,138 open reading frames. As suspected from physiological studies of heliobacteria that have failed to show photoautotrophic growth, genes encoding enzymes for known autotrophic pathways in other phototrophic organisms, including ribulose bisphosphate carboxylase (Calvin cycle), citrate lyase (reverse citric acid cycle), and malyl coenzyme A lyase (3-hydroxypropionate pathway), are not present in the H. modesticaldum genome. Thus, heliobacteria appear to be the only known anaerobic anoxygenic phototrophs that are not capable of autotrophy. Although for some cellular activities, such as nitrogen fixation, there is a full complement of genes in H. modesticaldum, other processes, including carbon metabolism and endosporulation, are more genetically streamlined than they are in most other low-G؉C gram-positive bacteria. Moreover, several genes encoding photosynthetic functions in phototrophic purple bacteria are not present in the heliobacteria. In contrast to the nutritional flexibility of many anoxygenic phototrophs, the complete genome sequence of H. modesticaldum reveals an organism with a notable degree of metabolic specialization and genomic reduction.

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“…This metabolic activity is probably related to their photosynthetic capacity, a common feature among Bradyrhizobium cluster (Giraud and Fleischman, 2004). Despite being diazotrophic, phototrophic free-living bacteria have never been discovered to date in the marine environment (Madigan, 1995;Riemman et al, 2010). We hypothesize though that similar to their closest relatives, the Mediterranean Bradyrhizobium detected in this study are able to acquire an independent source of energy through photosynthesis.…”

Section: Non-cyanobacterial Diazotrophs Richness Recoverymentioning

confidence: 99%

“…Conversely, non-cyanobacterial diazotrophs are considered unable to acquire an autonomous carbon source through photosynthesis, and have thus been neglected in biogeochemical studies (Madigan, 1995;Tyrell, 1999). However, this metabolic function has also recently been missing within UCYN-A , although these picocyanobacteria can actively express nifH gene and can reach high concentrations (Church et al, 2005b;Moisander et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Intriguing diversity among diazotrophic picoplankton along a Mediterranean transect: a dominance of rhizobia

2011

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Abstract. The Mediterranean Sea is one of the most oligotrophic marine areas on earth where nitrogen fixation has formally believed to play an important role in carbon and nitrogen fluxes. Although this view is under debate, the diazotrophs responsible for this activity have still not been investigated in the open sea. In this study, we characterised the surface distribution and species richness of unicellular and filamentous diazotrophs across the Mediterranean Sea by combining microscopic counts with size fractionated in situ hybridization (TSA-FISH), and 16S rDNA and nifH genes phylogenies. These genetic analyses were possible owing to the development of a new PCR protocol adapted to scarce microorganisms that can detect as few as 1 cell ml −1 in cultures. Low concentrations of diazotrophic cyanobacteria were detected and this community was dominated at 99.9% by picoplankton hybridized to the Nitro821 probe, specific for unicellular diazotrophic cyanobacteria (UCYN). Among filamentous cyanobacteria only 0.02 filament ml −1 of Richelia were detected in the eastern basin, while small (0.7-1.5 µm) and large (2.5-3.2 µm) Nitro821-targeted cells were recovered at all stations with a mean concentration of 3.5 cell ml −1 . The affiliation of the small Nitro821-targeted cells to UCYN-A was confirmed by 16S and nifH phylogenies in the western Mediterranean Sea. In the central and the eastern Mediterranean Sea no 16S rDNA and nifH sequence from UCYN was obtained as cells concentration were close to, or below PCR detection limit. Bradyrhizobium sequences dominated nifH clone libraries from picoplanktonic size fractions. A few sequences of γ -proteobacteria were also detected in the central Mediterranean Sea. While low phosphate and iron concentrations could explain the absence of Trichodesmium sp., the factors that prevent the developCorrespondence to: I. C. Biegala (biegala@univmed.fr) ment of UCYN-B and C remain unknown. We also propose that the dominating picoplankters probably developed specific strategies, such as associations with protists or particles, and/or photosynthetic activity, to acquire carbon for sustaining diazotrophy.

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Microbiology of Nitrogen Fixation by Anoxygenic Photosynthetic Bacteria

Cited by 45 publications

References 82 publications

Purification and Characterization of Alkaline Serine Proteinase from Photosynthetic Bacterium,Rubrivivax gelatinosusKDDS1

Purification and Characterization of Alkaline Serine Proteinase from Photosynthetic Bacterium,Rubrivivax gelatinosusKDDS1

The Genome of Heliobacterium modesticaldum , a Phototrophic Representative of the Firmicutes Containing the Simplest Photosynthetic Apparatus

Intriguing diversity among diazotrophic picoplankton along a Mediterranean transect: a dominance of rhizobia

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