Cell autoaggregation, biofilm development, and plant attachment in a Sinorhizobium meliloti lpsb mutant.

BOGINO, P., SORROCHE, F., MORALES, G., GIORDANO, W.

Encuentro; Sexto Encuentro de Física y Química de Superficies.; 2014

Bacterial surface molecules are crucial for establishment of successful rhizobia-legume symbiosis, and in most bacteria are also critical for adherence properties and surface colonization [1, 2]. Mutants defective in the production of exopolysaccharides (EPS), lipopolysaccharides (LPS), and capsular polysaccharides are usually affected in the process of root infection [3]. Here we evaluated the role of LPS in cell-cell and cell-surface interactions. Using Confocal Laser Scanning Microscopy (CLSM) the progression of biofilm development of GFPuv-tagged, EPS II-producing strains Rm8530 (wild type) and Rm8530 lpsB (LPS mutant), was determined. Biofilm formation was perturbed in Rm8530 lpsB, as compared to parental strain Rm8530. EPS II seems to be essential for the development of the ordered bacterial honeycomb-like arrays of the wild type strain, in which the rods adhere to each other through lateral interactions, forming rows of bacteria identically oriented. Despite that Rm8530 lpsB is able to synthesize EPS II, such structures were not visualized in mutant biofilms. Experiments combining theLPS and EPS mutants were able to showthat both polymers have an impact in cell-cell adhesive interactions leading to autoaggregation. Polar bacteria-bacteria adhesive interactions were increased in Rm8530 lpsB as compared to Rm8530 and typical zig-zag or bacterial bouquets formations were visualized only in the mutant. These observations indicate that the LPS has a role in determining cell-cell interactions. Such interactions were also detected when these strains were imaging by Atomic Force Microscopy (AFM). An altered LPS molecule increased bacterial adsorption to roots. Our findings clearly indicate that mutants in the core of LPS showed alterations in the formation of biofilmsand adhered to alfalfa roots in greater numbers than the wild strains withLPS, whereas the increased autoaggregation in these mutants was evident in the absence of EPS II.