Optical Control of Exopolysaccharide Production and Biofilm Formation in the Soil Bacterium Sinorhizobium Meliloti

The gram-negative soil bacterium Sinorhizobium meliloti fixes nitrogen in symbiotic association with alfalfa plants. Establishment of this symbiosis depends upon the exchange of small signaling molecules between the soil bacterium and its host. In particular, exopolysaccharides produced by S. meliloti are required for invasion of root nodules, through a process that is not well understood. There are two types of exopolysaccharides produced by S. meliloti: succinoglycans (also called EPS-I) and galactoglucans (also called EPS-II). Besides aiding plant root association, exopolysaccharides are also thought to play a key role in protecting rhizobium cells against various environmental stresses, such as desiccation. In addition to its signaling and protective function, exopolysaccharides, in particular EPS-II, play a critical role in the development of structured complex 3-D surface attached communities of microbial biofilms in soil. Thus, in-depth understanding of properties and functions of exopolysaccharides secreted by S. meliloti cells is critical for the development of next generation technologies. While studying the interactions of exopolysaccharides with soil particles and its effect on moisture retention, we needed a tool that would allow us spatiotemporally control the production of exopolysaccharides with high precision. Ideally, a tool that allows on demand control of exopolysaccharide production, irrespective of type of media used and surface exposed, with minimal intervention would be desirable for this purpose. Here we demonstrate the development of such tool that allows us to spatially control the production of EPS-II and biofilm morphology, with ~400 µm resolution, in S. meliloti by using previously reported light responsive DNA binding protein EL222.