Isolation,identification,metabolic characteristics,and functional gene detection of a nitrogen-fixing strain with hydrogen autotrophic ability of Serratia marcescens
Hydrogen-oxidizing bacteria(HOB)is a group of bacteria that can utilize oxygen to oxidize hydrogen to provide energy to fix carbon dioxide and autotrophic growth.Still,there is little research on HOB that can fix nitrogen meanwhile.Because some HOB often acts as plant growth-promoting rhizobacteria(PGPR)in nature,and nitrogen fixation is a possible growth-promoting mechanism,it is expected to obtain more nitrogen-fixing HOB from several functional communities.It is unknown whether there are both hydrogen-autotrophic and nitrogen-fixing Serratia.In this research,a pigment-producing nitrogen-fixing bacterial strain,NF-HOB1,was isolated from a nitrogen-fixing and hydrogen-oxidizing microbial community,which then was identified as Serratia marcescens by 16S rRNA gene sequencing(GenBank:OQ625884).The strain can grow by heterotrophic nitrogen fixation or hydrogen-autotrophic carbon fixation,verified through carbon/nitrogen source limited culture experiments,with a hydrogen oxidation rate of 0.1875 mmol/d.Polymerase chain reaction(PCR)amplification revealed that its plasmid DNA encodes the nitrogenase Fe-protein structural gene nifH,and the genome encodes species-specific ribose-1,5-diphosphate carboxylase(Rubisco)and hydrogenase 3 structural genes.The genome frame map sequencing further revealed the genomic characteristics of the strain,with a gene length of 4 919 531 bp and 4 778 protein-coding genes.It was annotated to find hydrogenase 2,carbonic anhydrase,and GlnK-type PⅡ protein,suggesting a carbon dioxide concentration mechanism and a potential global nitrogen regulation pathway characterized by NtrB-GInK-amtB/nifA.Gene Ontology(GO)and the Kyoto Encyclopedia of Genes and Genomes(KEGG)annotated 81.26％and 48.13％of genes,respectively.Combined with database analysis,it is speculated that the strain may have multiple plant growth-promoting functions.To conclude,Serratia is a potential hydrogen-oxidizing bacteria,and its rich metabolic characteristics will broaden its application prospects as a bacterial resource.
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