Isolation,Identification And Genome Analysis Of Microaerobic Autotrophic Sulfur-oxidizing Bacteria In The Sediments Of Pearl River

Sulfur-oxidizing bacteria?SOB?play an important role in the cycle of carbon,nitrogen and sulfur.At present,researches on sulfur oxidizing bacteria are mainly focused on aerobic and anaerobic SOB,while the research on microaerobic SOB is less.Moreover,there are some deficiencies in the study of metabolic pathway and oxidation mechanism of microaerobic SOB.In this study,the surface sediments of the Guangzhou section of the Pearl River were taken as sample to enrich microaerobic SOB.High-throughput sequencing technology was used to track the changes of bacterial community structure during the enrichment process.Microaerobic autotrophic SOB were isolated from enrichment.Strain LSR1 was isolated and identified as a new genus by studying its physiological,biochemical and genetic characteristics.Major metabolic pathways and regulatory mechanisms of strain LSR1 were studied by whole genome sequencing technology.The enrichment of SOB in surface sediment of the Pearl River was carried out under micro-oxygen conditions.High-throughput sequencing results showed that the abundance of SOB decreased with the enrichment process,and the proportion of SOB increased.The main SOB in the enrichment included Thiobacillaceae_unidentified?Sulfuricurvum,Geothrix,Bacillus,Thiofaba and Thiomonas.Eight strains of SOB were isolated from the third-generation enrichment.They had high homology with Thiomonas,Zoogloea,Azonexus,Pseudomonas and Sulfuritortus,respectively.The similarity between strain LSR1 and Sulfuritortus calidifontis J1A was 93%?less than 95%?.Phase taxonomic identification of strain LSR1 showed that it was Gram-negative.The optimum growth temperature of strain LSR1 was 25-30 C and the optimum growth pH was 6.5-7.0.It can grow under microaerobic conditions,and also can grow under anaerobic conditions with nitrate as electron acceptor.NaHCO₃ can be used as carbon source,nitrate,N₂ and ammonium salt as nitrogen source,thiosulfate and low concentration sulfide?2mM Na₂S?as sulfur source,but other organic carbon source,nitrite and sulfur source used in the experiment can not grow.On the basis of phenotypic,genotypic and phylogenetic analysis,strain LSR1represents a novel species of a new genus in the family Thiobacillaceae.A genomic study on the strain LSR1 showed that the genome size of strain LSR1 was3.2Mb,with 3,219 genes.Strain LSR1 contained the sulfide,thiosulfate and sulfite oxidation pathways,and did not contain a complete TCA cycle;the main way of strain LSR1 to use nitrate was the dissimilation of nitrate reduction pathway;strain LSR1 contained a variety of nitrogenase genes and nitrogenase regulation genes,and the lack of oxygen and nitrogen sources would promote the expression of nitrogenase;contained two kinds of high oxygen affinity terminal oxidase?cbb3 oxidase oxidase and bd oxidase oxidase?;the final electron acceptor of microaerobic and anaerobic growth of strain LSR1 is oxygen and nitrate/nitrite respectively,high oxygen content suppressed the gene expression of cbb3 oxidase,high oxidation reduction stress promoted the gene expression of cbb3 oxidase genes,bd oxidase oxidase genes and electron transport chain genes;LSR1 contained a variety of antioxidant genes such as oxide dismutase gene,peroxidase gene and catalase gene,which could maintain the microaerobic growth of LSR1.