Function Analysis of Choline Binding Domains of LytA, LytC and CbpD in The Biofilm Formation Process of Streptococcus Pneumoniae
Abstract Background: Choline binding proteins (CBPs) are a family of proteins that can interact with pneumococcal cell wall by choline binding domains (CBDs). In this study, we found a modified choline binding repeat (ChBp-I) with a pI of 7.66 can promote the development of biofilm in vitro. Thus, we aim to characterize the function of CBDs of LytA, LytC and CbpD in biofilm formation.Results: By transcriptome analysis, 81 genes were identified as down regulated and 138 genes were up regulated (|log2 fold change|≥1.5) under ChBp-I of 50mg/L. The up regulated genes are well clustered in membrane transport (carbohydrate, lipid, protein, cation and phosphate) and carbohydrate metabolism (fructose, mannose, galactose, starch, sucrose, amino sugar and nucleotide) related pathways. The up-regulated genes are mostly regulated the same under CBD-A, CBD-C and CBD-D. Phenotype analysis reveal high concentrations of CBD-C and CBD-D (>100μg/mL) but not CBD-A (negative charged) can promote the biofilm formation. Meanwhile, the existence of CBD-C and CBD-D promote the growth rate and both CBDs inhibit the autolysis of pneumococcal cell. By component analysis, these three CBDs were proved involved in the regulation of extracellular DNA, protein, cation and phosphate, and promote the forming of insoluble precipitates.Conclusions: The binding of CBPs can influence the membrane transport pathways and react with extracellular DNA and protein to promote biofilm formation in S. pneumoniae.