| Phenotypic plasticity is ubiquitous in the biosphere, but relatively few studies on the microbial field, and there are few reports about using molecular marker technology to study microbial phenotype plasticity. One E. coli strain and 45 Staphylococcus aureus strains were adopted and mixed together and cultured to construct a competitive environment, and determined their growth volume and did GWAS (genome wide association study) comparison with the growth volume of the same initial concentration of the S. aureus cultured alone, and obtained significant SNP sites. Analyzed the expression variation correlated with the growth variation of S. aureus within the SNP sites, and studied the precision of their phenotypic plasticity of S. aureus. Based on the growth volume of 45 S. aureus strains under two modes and the sequencing results of full genotype, and adopted bi variable GWAS to screen the SNP sites that significantly correlated to growth volume of S. aureus,and localized the S. aureus genes corresponding to these SNP sites, and screened from the functions of these genes that correlated to the part of the growth variation of S. aureus to summarize and analyze. Then selected scdA sequence with relatively strong precision among them as template to design primer, using relative quantitative method of real time fluorescence quantitative PCR (qPCR), selected and used 16S rRNA as internal reference gene to measure the gene mRNA expression under two culture environment, then statistically analyzed the differences. The results showed that the growth volume of S. aureus mixed cultured with E. coli significantly declined. 415 obvious SNP sites were checked out by GWAS at 12 sampling sites, and after screening the expression of scdA gene under two culture conditions was measured and analyzed statistically. The results showed that regardless of base of A or G of 251050 site, the relative expression of scdA gene in mixed culture was significantly higher than that in the single culture. Therefore, the sequencing results showed that during the whole culturing process the genotype of scdA remained unchanged. In order to respond the environmental stress, the scdA gene corresponding to S. aureus SNP25150 expression under the mixed culture environment was significantly boosted, to maintain its own stability in the culture system. This suggested that S. aureus could make responses by taking the initiative in diversity according to the environmental signals at the respects of physiological phenotype in broad sense, this could also considered as the reflection of phenotypic plasticity of S. aureus under environmental changes. |
