Cold adaptation in Bacillus subtilis under anaerobic conditions

JANA BERANOVA; MARIA CECILIA MANSILLA; DIEGO DE MENDOZA; IVO KONOPASEK

Estambul, Turquia

Congreso; International Union of Microbiological Societies (IUMS) Conference; 2008

Grampositive soil bacterium Bacillus subtilis was generally considered to be strict aerobe. Nevertheless it was proved recently that this organism is able of anaerobic growth using nitrate respiration. We studied the adaptation of B. subtilis membrane to the cold shock and to steady state growth at low temperature under anaerobic conditions. Bacillus subtilis employs cold-inducible fatty acid desaturase (Des) to increase its membrane fluidity by fatty acid desaturation. After sudden decrease in temperature, transcription of the des gene is induced by the increase in membrane order and it is switched off when membrane fluidity is restored. The des expression is exclusively regulated by the two-component system desK-desR, with membrane-bound DesK acting as a sensor of membrane fluidity. We studied the fatty acid adaptation at lower temperature under anaerobic conditions finding almost the same pattern of fatty acid changes when compared with aerobic cultivation. As the desaturase of B. subtilis requires molecular oxygen for its activity we decided to study how anaerobic conditions affect the DesK-DesR mediated cold shock adaptation. To that end we used strain AKP3 containing a fusion of the lacZ gene to the des promoter integrated ectopically at the non-essential amyE locus of B. subtilis. The level of Des was also measured as the intensity of fluorescence, using a strain bearing isotopic Des-GFP fusion. AKP3 was grown in either aerobic or anaerobic conditions (nitrate respiration) and assayed for â-galactosidase activity after temperature shift from 37°C to 25°C. The same experiment was performed with the strain with des deletion and the same reporter system (AKP4). Under aerobic condition the â-galactosidase activity of AKP3 increased and reached the plateau after 2 hours after the temperature shift. In AKP3 and AKP4 strains growing under anaerobic conditions we observed high â-galactosidase induction which did not reach any plateau within 6 hours after the shock. This high induction was significantly reduced by adding external unsaturated fatty acids (UFAs) to the medium at the moment of cold shock. Therefore we assume that both under anaerobic and aerobic conditions the DesK-DesR mediated des expression despite the fact that during anarobiosis Des synthesis cannot support membrane fluidization – the fluidisation itself arises only from a new equilibrium of iso-/anteiso branched fatty acid composition.