EmbRS a new two‐component system that inhibits biofilm formation and saves Rubrivivax gelatinosus from sinking

Abstract

Photosynthetic bacteria can switch from planktonic lifestyle to phototrophic biofilm in mats in response to environmental changes. The mechanisms of phototrophic biofilm formation are, however, not characterized. Herein, we report a two-component system EmbRS that controls the biofilm formation in a photosynthetic member of the Burkholderiales order, the purple bacterium Rubrivivax gelatinosus. EmbRS inactivation results in cells that form conspicuous bacterial veils and fast-sinking aggregates in liquid. Biofilm analyses indicated that EmbRS represses the production of an extracellular matrix and biofilm formation. Mapping of transposon mutants that partially or completely restore the wild-type (WT) phenotype allowed the identification of two gene clusters involved in polysaccharide synthesis, one fully conserved only in Thauera sp., a floc-forming wastewater bacterium. A second two-component system BmfRS and a putative diguanylate cyclase BdcA were also identified in this screen suggesting their involvement in biofilm formation in this bacterium. The role of polysaccharides in sinking of microorganisms and organic matter, as well as the importance and the evolution of such regulatory system in phototrophic microorganisms are discussed.

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

“…Two extreme cases were sampled in our experiments of Hg(II) binding affinity of intact cells of Rvx. gelatinosus (Steunou et al, 2013). In the planktonic mode of living, the diffusion step is much faster than that through the membrane (kd >> ka).…”

The biophysics of a critical phenomenon: colonization and sedimentation of the photosynthetic bacteria Rubrivivax gelatinosus

“…gelatinosus, sudden colonization and sinking of the cells occur. While the basics of the molecular mechanism, the regulatory pathways and the physiological impact (switch of the lifestyle from planktonic to biofilm) have been largely revealed (Steunou et al 2013), the biophysics of the process remained completely obscure. In the present study, we have attempted to address this issue.…”

“…The purple nonsulfur bacterium Rvx. gelatinosus is able to produce extracellular polymeric substances that form the matrix of the biofilm which plays determining role of sinking of the cells (Steunou et al 2013). The polysaccharides start to form at the early exponential phase of the cell growth.…”

Formation characteristics of an anoxygenic photosynthetic bacterial biofilm in a photorotating biological contactor for azo dye wastewater treatment

“…Most photobioreactors used for wastewater treatment with APB are based on suspended cultures because APB have poor flocculation and biofilm‐forming ability . It is difficult to achieve high APB density, effective retention and separation of APB biomass . However, compared with suspended growth processes, biofilm systems in wastewater treatment have advantages, including flexible operation, less hydraulic retention time, resilience to physical and chemical forces (such as shear flow and toxic substances), increased biomass retention time and concentration, accelerated degradation of recalcitrant compounds, reduced sludge production, better biomass settleability, and better effluent quality …”

“…Conversely, aggregated photosynthetic bacteria settle to the aphotic zone and thus are deprived of sunlight. Therefore, photosynthetic bacteria commonly decrease the quantities of EPS production to prevent the formation of flocs and fast‐sinking aggregates . The application of APB is limited by their low flocculation ability, which leads to difficulty in cell separation.…”