The Diversity And Sulfur Metabolic Pathway Of Sulfur Oxidizing Bacteria In The Pearl River Water

Sulfur-oxidizing bacteria（SOB）are the main participant in the sulfur biological oxidation,which pay important role in the sulfur biogeochemical cycle,The Pearl River is the second largest river in China,whose ecosystem is significant to the society and economics of Southern China.This paper studied the community composition,diversity,and species abundance of the sulfur oxidizing bacteria（SOB）in Guangzhou section of the Pearl River.In this study,water samples were collected from Baixianke（BXK）,Tanwei（TW）,Nansha（NS）and Suishi（SS）that located in the upper,middle and down stream of Guangzhou section.The cbbL and cbbM genes,which encoded two forms of ribulose-1,5-bisphosphate carboxylase/oxygenase（Rubis CO）,a key enzyme in the process of CO₂ fixation,were applied to study the community of autotrophic bacteria.Meanwhile the sox B,Sqr,and dsr A genes,which encoded key enzymes in the process of sulfur metabolism,were used to as the target genes for high-throughput sequencing and Q-PCR.eight SOB strains were isolated from SS water.Among these strains,a strain named LS2 was chosen to studied the physiological and biochemical characteristics,and metabolism pathyway on genome-wide.High-throughput sequencing showed the CO₂ fixation bacteria and sulfur oxidizing bacteria are widely distributed in the the upper water of Pearl River;most of these bacteria belong to Betaproteobacteria,mainly conclude Cupriavidus,Rubrivivax,Azoarcus,Thiobacillus,Methylibium,Hydrogenophaga,Leptothrix,Polaromonas,Thiobacillus,Sulfuritale,Sulfuritalea,Sulfurisoma,Thiobacillus,Sulfuricella,Comamonas,Dechloromonas,Sulfuritalea,Thiobacillus,Leptothrix,Polynucleobacter,Janthinobacterium,Hydrogenophaga,Acinetobacter,Sulfuricella,Sideroxydans,Others belong to Alphaproteobacteria,mainly conclude Rhodopseudomonas,Magnetospira,Magnetospirillum,Paracoccus,Gammaproteobacteria,mainly conclude Halothiobacillus,Halochromatium,Thioalkalicoccus,Aeromonas,Acinetobacter,and Deltaproteobacteria,mainly conclude Desulfurivibrio.Cyanobacteria were also responsible for the CO₂ fixation,and the genus of Synechococcus was the main group,relative aboundance reach up to 6.07%.The results of alpha diversity suggested the bacterial community in NS site is significantly different from the other sites.The abundance of dsrA gene is lower than soxB and Sqr genes,and the cbbM gene is lower than cbbL.The CO₂-fixing bacteria are dominant by the SOB,which indicated the important role of SOB in carbon and sulfur biochemistry cycles.Eight SOB strains were isolated from Pearl River.The 16 s rRNA gene identification suggested that they are closely related to the genera of Halothiobacillus,Thiomonas,Azospirillum and Halomonas.The similarity between LS2 and other four Halothiobacillus sequences was less than 96%.Because the strain LS2 has cbbL,cbbM,Sqr and soxB genes in its genome,we sequenced its whole genome to study the CO₂-fixing pathway and sulfur metabolic pathway on genome wide.The strain LS2 could tolerate 60g/L of NaCl,and use nitrate and ammonium as nitrogen source,thiosulfate and sulfur is the best sulfur sources for its growth.Based on the analysis of whole genome sequence,strain LS2 has complete Sox enzyme system,SQR and SOR enzymes,catalyzed S⁰、 S^2-、 S₂O₃^2-、 SO₃^2-finally oxidized to SO42-.In its carbon metabolism pathyway,we found LS2 can produce glucose 3-phosphoglycerate and pyruvate by glycolytic pathway,pyruvate can be further oxidized to acetyl CoA and acetate,and CO₂ fixed conducted by Calvin cycle.What’s more,it can get nitrogen source by nitrogen fixation,urea degradation and dissmilatory nitrate reduction.To survive in poor environment,LS2 had several mechanisms to resist heavy metals,low pH,high salt and oxidative stress such as various cation channels and special enzymes.