Characterization of promoter elements responsive to the quorum sensing (QS) auto-inducer 2 (AI-2) in Zymomonas mobilis

Abstract

The gram-negative bacterium Zymomonas mobilis presents several characteristics that make it suitable for industrial production of different bioproducts, including bioethanol. For example, Z. mobilis can be grown under both aerobic and anaerobic conditions, is capable of converting glucose to ethanol with an even greater efficiency than Saccharomyces cerevisiae itself and tolerates higher concentrations of this alcohol during the fermentation process. In addition, genetic manipulation techniques have been developed for this bacterium, which has been genetically modified and/or adapted to produce several value-added products of high economic interest (such as levan, sorbitol, lactate, polyhydroxybutyrate and 2,3-butanediol, among others). Moreover, additional genetic manipulations have also resulted in strains capable of incorporating alternative carbon sources into their metabolic pathways, such as the pentoses xylose and arabinose. Thus, Z. mobilis is currently regarded as a microorganism of great potential for the bioconversion industry and a better understanding of the mechanisms that control expression of its genes may aid the development of new genetically manipulated strains to assist in a variety of industrial applications. In this sense, it has been recently demonstrated that Z. mobilis is able to respond to the type 2 quorum sensing (QS) inducer, known as auto-inducer 2 (AI-2). AI-2 is one of the molecules used by bacteria to control the QS process, responsible for assessing the cellular density in their surrounding environment and synchronizing bacterial behavior at a community-scale level. Activation of the QS response leads to a decrease in the rate of cellular growth, while activates expression of genes involved in a range of alternative activities. Thus, if genes of industrial interest are incorporated into the Z. mobilis genome, under the control of AI-2 responsive promoters, it would be possible to induce their expression in a controlled way, by adding this signaling molecule to Z. mobilis cultures, since, although sensitive to AI-2, this bacterium is not capable of synthesizing it. Thus, the project proposed herein aims at characterizing Z. mobilis response to the QS autoinducer AI-2, identifying the genes/operons that have their expression modulated in response to this molecule, as well as the cis- and trans-acting elements (promoters and transcription factors) that mediate this process. These studies will lead to the isolation and functional characterization of first inducible promoters in Z. mobilis, which can be developed (and eventually patented) into an important tool for Z. mobilis manipulation, with possible application in a wide variety of industrial bioproceses, allowing the expression of transgenes in this bacterium, under controlled and optimized conditions. (AU)