Dataset Information

Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium Thermoleptolyngbya sp. O-77.

ABSTRACT: Cyanobacteria are widely distributed in marine, aquatic, and terrestrial ecosystems, and play an important role in the global nitrogen cycle. In the present study, we examined the genome sequence of the thermophilic non-heterocystous N2-fixing cyanobacterium, Thermoleptolyngbya sp. O-77 (formerly known as Leptolyngbya sp. O-77) and characterized its nitrogenase activity. The genome of this cyanobacterial strain O-77 consists of a single chromosome containing a nitrogen fixation gene cluster. A phylogenetic analysis indicated that the NifH amino acid sequence from strain O-77 was clustered with those from a group of mesophilic species: the highest identity was found in Leptolyngbya sp. KIOST-1 (97.9% sequence identity). The nitrogenase activity of O-77 cells was dependent on illumination, whereas a high intensity of light of 40 ?mol m-2 s-1 suppressed the effects of illumination.

SUBMITTER: Yoon KS

PROVIDER: S-EPMC5745016 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium Thermoleptolyngbya sp. O-77.

Yoon Ki-Seok KS Nguyen Nga T NT Tran Kien Trung KT Tsuji Kohsei K Ogo Seiji S

Microbes and environments 20171123 4

Cyanobacteria are widely distributed in marine, aquatic, and terrestrial ecosystems, and play an important role in the global nitrogen cycle. In the present study, we examined the genome sequence of the thermophilic non-heterocystous N<sub>2</sub>-fixing cyanobacterium, Thermoleptolyngbya sp. O-77 (formerly known as Leptolyngbya sp. O-77) and characterized its nitrogenase activity. The genome of this cyanobacterial strain O-77 consists of a single chromosome containing a nitrogen fixation gene c ...[more]

PMID: 29176306

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Project description:Cyanobacteria are oxygenic photosynthetic prokaryotes with important roles in the global carbon and nitrogen cycles. Unicellular nitrogen-fixing cyanobacteria are known to be ubiquitous, contributing to the nitrogen budget in diverse ecosystems. In the unicellular cyanobacterium Cyanothece sp. strain ATCC 51142, carbon assimilation and carbohydrate storage are crucial processes that occur as part of a robust diurnal cycle of photosynthesis and nitrogen fixation. During the light period, cells accumulate fixed carbon in glycogen granules to use as stored energy to power nitrogen fixation in the dark. These processes have not been thoroughly investigated, due to the lack of a genetic modification system in this organism. In bacterial glycogen metabolism, the glgX gene encodes a debranching enzyme that functions in storage polysaccharide catabolism. To probe the consequences of modifying the cycle of glycogen accumulation and subsequent mobilization, we engineered a strain of Cyanothece 51142 in which the glgX gene was genetically disrupted. We found that the ΔglgX strain exhibited a higher growth rate than the wild-type strain and displayed a higher rate of nitrogen fixation. Glycogen accumulated to higher levels at the end of the light period in the ΔglgX strain, compared to the wild-type strain. These data suggest that the larger glycogen pool maintained by the ΔglgX mutant is able to fuel greater growth and nitrogen fixation ability.IMPORTANCE Cyanobacteria are oxygenic photosynthetic bacteria that are found in a wide variety of ecological environments, where they are important contributors to global carbon and nitrogen cycles. Genetic manipulation systems have been developed in a number of cyanobacterial strains, allowing both the interruption of endogenous genes and the introduction of new genes and entire pathways. However, unicellular diazotrophic cyanobacteria have been generally recalcitrant to genetic transformation. These cyanobacteria are becoming important model systems to study diurnally regulated processes. Strains of the Cyanothece genus have been characterized as displaying robust growth and high rates of nitrogen fixation. The significance of our study is in the establishment of a genetic modification system in a unicellular diazotrophic cyanobacterium, the demonstration of the interruption of the glgX gene in Cyanothece sp. strain ATCC 51142, and the characterization of the increased nitrogen-fixing ability of this strain.

Project description:BACKGROUND:The metabolic capacity for nitrogen fixation is known to be present in several prokaryotic species scattered across taxonomic groups. Experimental detection of nitrogen fixation in microbes requires species-specific conditions, making it difficult to obtain a comprehensive census of this trait. The recent and rapid increase in the availability of microbial genome sequences affords novel opportunities to re-examine the occurrence and distribution of nitrogen fixation genes. The current practice for computational prediction of nitrogen fixation is to use the presence of the nifH and/or nifD genes. RESULTS:Based on a careful comparison of the repertoire of nitrogen fixation genes in known diazotroph species we propose a new criterion for computational prediction of nitrogen fixation: the presence of a minimum set of six genes coding for structural and biosynthetic components, namely NifHDK and NifENB. Using this criterion, we conducted a comprehensive search in fully sequenced genomes and identified 149 diazotrophic species, including 82 known diazotrophs and 67 species not known to fix nitrogen. The taxonomic distribution of nitrogen fixation in Archaea was limited to the Euryarchaeota phylum; within the Bacteria domain we predict that nitrogen fixation occurs in 13 different phyla. Of these, seven phyla had not hitherto been known to contain species capable of nitrogen fixation. Our analyses also identified protein sequences that are similar to nitrogenase in organisms that do not meet the minimum-gene-set criteria. The existence of nitrogenase-like proteins lacking conserved co-factor ligands in both diazotrophs and non-diazotrophs suggests their potential for performing other, as yet unidentified, metabolic functions. CONCLUSIONS:Our predictions expand the known phylogenetic diversity of nitrogen fixation, and suggest that this trait may be much more common in nature than it is currently thought. The diverse phylogenetic distribution of nitrogenase-like proteins indicates potential new roles for anciently duplicated and divergent members of this group of enzymes.

Dataset Information

Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium Thermoleptolyngbya sp. O-77.

Publications

Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium Thermoleptolyngbya sp. O-77.

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