Biofilm formation of Bdellovibrio bacteriovorus host-independent derivatives

Bdellovibrios are Gram-negative predatory bacteria which are ubiquitous to many environmental niches, including natural biofilms. In this study, host-independent (HI) variants of Bdellovibrio bacteriovorus 109J were isolated. Predation assays and genetic analysis confirmed that the selected HI variants are derivatives of B. bacteriovorus. When grown in microtiter plates, HI variants were able to form tenacious biofilms on the surface of the wells. HI biofilm formation on different surfaces, media and temperatures was examined. HI biofilm development was seen on all of the examined surfaces, with the most robust biofilm developing at 22 degrees C and in media supplemented with yeast extract. Biofilm detachment experiments revealed that the HI cells are firmly attached to the surface of the wells and are not easily removed by physical and chemical treatments. Treating the biofilm with proteinase K and DNase-I caused rapid detachment of the biofilm as well as inhibition of biofilm formation, suggesting that DNA and proteins are major components of the HI biofilm extracellular matrix. Our data suggest that under conditions that might favor the development of HI variants, such as a rich nutrient environment, Bdellovibrio facultative prey cells are capable of attaching to abiotic surfaces and forming biofilms.