Cell Size Distribution And Its Taxonomic Feature In Human Intestinal Bacteria

The cell size of microorganisms is a basic and important feature that should be considered as an important reference factor for cell physiology and ecological function research.The microbial cell volume varies greatly in the environment.The molecular ecology technology used in environmental microbiology research currently ignores the cell size diffrence between microorganisms.In this paper,human intestinal bacteria were used as the research object.Through size-fraction filtration,absolute cell number and high-throughput sequencing technology,tne correlation between the intestinal bacterial cell size and species,genome size,rRNA gene copy number and its expression were analyzed.The following conclusions are drawn:(1)The results of cell size identification obtained from multiple individual sources show a high degree of consistency,indicating that the method used in this study can effectively achieve size-fraction and species identification in most intestinal microbial bacteria synchronously.(2)The cell size defined by the single gene(16S rRNA gene and rpoB gene)level and the genome(bins)level is very close,and the relative standard deviation is 1.6%-18.5%for the same species.(3)The bacteria that 16S rRNA sequence very similarity(>99%)have higher probability of similar cell size,and with the similarity decreasing(99%-90%),cell size differences is also increasing.(4)Accompanying the increase of cell size in intestinal microbes,cell genome size,rRNA gene copy number and expression show an increasing trend,suggesting the potential association between cell size and genomic evolution and physiological characteristics.In summary,this study is the first to explore the correlation between the size of intestinal flora bacteria and species classification,genomic characteristics and so on,the results will help to supplement the existing microbial molecular ecology research to ignore the lack of cell size information,the relevant experimental and analytical methods can be applied to other environmental flora systems.