Transcriptional expression of six genes located on pBSSB1 of Salmonella enterica serovar Typhi in different growth phases and environmental stresses.

A linear plasmid pBSSB1 of z66-positive Salmonella enterica serovar Typhi was previously identified to be involved in unidirectional flagellar phase variation due to the expression and regulation of fljB(z66) and fljA located on it. However, the expression of the remaining genes and other possible functions of pBSSB1 have not been reported yet. Here, we investigated the transcriptional expression characteristics of six genes (002, 008, 012, 017, 021, and 026) located on the linear plasmid pBSSB1 in different growth phases and environmental stresses by means of qRT-PCR. The results show that these six genes are all transcribed in normal growth condition (LB broth at 37 °C with stirring 250 rpm), and their expression has an increasing trend in general with the growth of the bacteria. Under environmental stresses, there is an increase in expression levels of 002, 008, 012, and 026, while no significant change in expression was observed for 017 and 021. In addition, the expression levels and modes of 017 and 021 are similar in all the growth conditions. To our knowledge, this is the first report describing the transcriptional expression characteristics of these six genes located on pBSSB1 and suggesting that pBSSB1 may be very important in response to the environmental stresses in z66-positive S. enterica serovar Typhi.