Genomic Analysis Of Burkholderia Glumae And Screening Of Their Horizontal Transfer Genes

Bacterial panicle blight caused by Burkholderia glumae is a serious seed-borne disease of rice.B.glumae can infect rice and infect human lungs.B.glumae widely exist in environments such as soil.Therefore,B.glumae is considered to have strong niche adaptation and pathogenicity.Horizontal gene transfer(HGT)is an important driving force for bacterial evolution.HGT plays an important role in enhancing the niche adaptation and pathogenicity of bacteria.In this paper,the evolutionary of B.glumae was studied from the perspective of HGT.The purpose is to explore the effects of HGT on the pathogenicity and niche adaptation of B.glumae.Firstly,a strain of B.glumae from China named HN was whole genome sequenced The size of HN complete genome was 5,844,653 bp,which was consisted of 2 chromosomes and 1 plasmid.Gene annotation revealed a total of 7239 CDS features in the genome.Pathogenic gene analysis showed that there are 39 pathogenicity-related genes in HN strains,and these genes can be classified into two categories:21 genes including the toxoflavin gene cluster are related to bacterial panicle blight and 7 genes including the phenylacetyl-CoA monooxygenase complex are related to cystic fibrosis.This result suggested that HN may be able to infect human and rice.Secondly,the role of HGT in the evolution of B.glumae.Evolutionary analysis showed that 9 B.glumae strains appeared on four different branches,suggested that B.glumae has at least four different evolutionary pathways.Among them,HN strain and other strains have a large evolutionary distance.The core and pan genome analysis of B.glumae showed that the core genome of B.glumae includes 3246 genes,and the pan-genome includes 7092 genes,suggesting that B.glumae is versatile and niche adaptability.3 isolates of rice with complete genome(HN,BGR1,LMG2196)and 1 isolate of human AU6208 were used to screen the horizontal transferred genes by constructing phylogenetic trees.Of the four strains,43,41,50,and 43 horizontal transferred genes were screened,respectively.Interestingly,these horizontal transferred genes contain two pairs of genes:sbnA/sbnB and pehA/pehB,and three gene clusters that synthesize Massettolide A,pyrroloquinoline and phenazine,respectively.Among them,sbnA/sbnB only exists in AU6208,others are core genes.Functional analysis of two horizontal transfer gene pairs.The sbnA/sbnB were transferred from Streptomyces to the AU6208 by one HGT.The enzymes encoded by bnA and sbnB can produce L-2,3-diaminopropionic acid by catalytic reaction.L-2,3-diaminopropionic acid is a key precursor in the synthesis of many antibiotics such as viomycin and capreomycin and a precursor of staphyloferrin B(SB)a siderophore produced by Staphylococcus aureus.SB is required for normal growth in the presence of mammalian serum,and inactivation of the SB biosynthetic operon was impaired for virulence.pehA and pehB were transferred from other species to B.glumae by two independent HGT.They encode two highly similar endopolygalacturonases.In Burkholderia cepacia,pehA is involved in the maceration of onion bulbs;in Erwinia carotovora,pehA and regulators of pehA gene expression are required for virulence.Therefore,the two groups of genes are closely related to niche adaptation and pathogenicity of bacteria.Functional analysis of three horizontally transferred gene clusters.Massetolide A synthetic gene cluster were transferred from Pseudomonas,contained 13 genes,which encoded a cyclic lipopeptide(CLP)antibiotic with broad-spectrum antimicrobial activities.Massetolide A production is essential in swarming motility of Pseudomonas fluorescens and plays an important role in biofilm formation.The pyrroloquinoline quinone synthesis gene cluster includes 5 genes of pqqABCDE,pqqBCDE were transferred from Pseudomonas.Pyrroloquinoline quinone is a redox cofactor and an antioxidant that prevent cell damage caused by reactive oxygen.The phenazine synthesis gene cluster includes 7 genes of phzBCDEFGI were transferred from actinomycetes.Phenazine may function as electron shuttles,facilitating bacterial and plant access to iron and nutrients such as phosphate.Similarly,pyocyanin deficient mutants were less competitive and less virulent than wild-type Pseudomonas aeruginosa in mouse acute and chronic pneumonia infection models.Therefore,the three gene clusters are closely related to niche adaptation and pathogenicity of bacteria.In summary,genomic analysis revealed that B.glumae obtained a large number of foreign genes from other bacteria through HGT.These genes synthesize secondary metabolites or their precursors,which promote growth,enhance resistance and virulence.These genes may be important for pathogenicity and niche adaptation of B.glumae that will be verified later.These results have guiding significance for understanding of the evolutionary process of B.glumae and the precise development of high-efficiency preventive reagent.