Physiological Function of Rac Prophage During Biofilm Formation and Regulation of Rac Excision in Escherichia coli K-12.

Xiaoxiao Liu,Yunxue Guo,Xingsheng Cai,Zhenshun Zeng,Thomas K Wood,Xiaoxue Wang,Baiyuan Li,Yangmei Li

doi:10.1038/srep16074

Abstract

Rac or rac-like prophage harbors many genes with important physiological functions, while it remains excision-proficient in several bacterial strains including Escherichia coli, Salmonella spp. and Shigella spp. Here, we found that rac excision is induced during biofilm formation, and the isogenic stain without rac is more motile and forms more biofilms in nutrient-rich medium at early stages in E. coli K-12. Additionally, the presence of rac genes increases cell lysis during biofilm development. In most E. coli strains, rac is integrated into the ttcA gene which encodes a tRNA-thioltransferase. Rac excision in E. coli K-12 leads to a functional change of TtcA, which results in reduced fitness in the presence of carbenicillin. Additionally, we demonstrate that YdaQ (renamed as XisR) is the excisionase of rac in E. coli K-12, and that rac excision is induced by the stationary sigma factor RpoS through inducing xisR expression. Taken together, our results reveal that upon rac integration, not only are new genes introduced into the host, but also there is a functional change in a host enzyme. Hence, rac excision is tightly regulated by host factors to control its stability in the host genome under different stress conditions.

Highlights

Bacteriophages and bacteria are the most abundant life forms on Earth
We addressed both questions and found that rac excision in E. coli K-12 is induced during biofilm formation, and we found that the rac deletion strain formed more biofilm in nutrient rich medium at early stages and showed high swimming motility
Biofilms are the preferred lifestyle of bacteria, and prophages are involved in biofilm formation[8,30]; we tested whether prophage excision is regulated during biofilm formation in E. coli K-12 BW25113

Summary

Introduction

Bacteriophages and bacteria are the most abundant life forms on Earth. Bacteria and phages interact frequently, and each phage infection has the potential to introduce new genetic information into the bacterial host, thereby driving the evolution of bacteria. Prophage-encoded virulence factors make important contributions to pathogenesis, including those of Corynebacterium diphtheriae (diphtheria), Clostridium botulinum (botulism), and E. coli O157:H7 (Shiga-like toxin)[5] Active prophages such as Gifsy-2 can give the Salmonella host a competitive advantage by killing competitors and by providing immunity[6]. In the human pathogen Listeria monocytogenes, integration of prophage A118 disrupts the host gene comK encoding the major competence transcription factor[17], and excision of A118 restores the function of comK18. RecE and RecT in rac are involved with RecA-dependent recombination[27] It harbors important genes, rac remains excision proficient in E. coli K-12 and in the Sakai strain[7,22]. In addition to the previously identified host factor H-NS, we found that the sigma factor RpoS increased rac excision by regulating the transcription of xisR at the stationary phase

Methods

Results

Conclusion