Project description:Previously, we discovered that the global regulator Hha is related to cell death in biofilms and regulates cryptic prophage genes. Here we show Hha induces excision of prophage CP4-57 and DLP12 by inducing excision genes and by reducing SsrA synthesis. SsrA is a tmRNA important for rescuing stalled ribosomes, contains an attachment site for CP4-57, and is shown here to be required for CP4-57 excision. These prophages impact biofilm development as deletion of 35 genes individually of prophage CP4-57 and DLP12 increase biofilm formation up to 17-fold, and 5 genes decrease biofilm formation up to 6-fold. In addition, CP4-57 excises during early biofilm development but not in planktonic cells, whereas DLP12 excision was detected at all the developmental stages for both biofilm and planktonic cells. CP4-57 excision leads to a chromosome region devoid of the prophage and formation of a phage circle (which is lost). These results were corroborated by a whole-transcriptome analysis that showed that complete loss of CP4-57 activated expression of the flg, flh, and fli motility operons and repressed expression of key enzymes in the tricarboxylic acid cycle and enzymes for lactate utilization. Prophage excision also results in the expression of cell lysis genes that reduce cell viability (e.g., alpA, intA, and intD). Hence, defective prophage are involved in host physiology via Hha and in biofilm formation by generating a diversified population with specialized functions in terms of motility and nutrient metabolism.
