Role of the Bacillus subtilis fatty acid desaturase in membrane adaptation during cold shock

Abstract

SummaryIn our attempt to understand the cold shock response of Bacillus subtilis, we report on the role of the B. subtilis fatty acid desaturase (FA-D) Des during membrane adaptation to low temperatures and demonstrate its importance during cold shock. A des null mutant was constructed and analysed in comparison with its parental strain. Growth studies and large-scale comparative fatty acid (FA) analysis revealed a severe cold-sensitive phenotype of the des deletion mutant during the absence of isoleucine and showed that four unsaturated fatty acid (UFA) species differing in length, branching pattern and position of the double bond are synthesized in B. subtilis JH642 but not in the des null mutant. Apart from the lack of UFA synthesis, the FA-D deletion strain showed a dramatically altered saturated fatty acid (SFA) profile at the onset of the stationary growth phase in the presence of exogenous isoleucine sources. Expression of des integrated in trans at the amyE locus of the des deletion strain not only cured the cold-sensitive phenotype observed for the des mutant but allowed much better growth than in strain JH642 after a shift from 378C to 158C. These results show that, during cold shock adaptation, des expression can completely replace the isoleucinedependent, long-term, FA branching adaptation mechanism. We conclude that the crucial aspect in cold adaptation of the cytoplasmic membrane is not its specific molecular composition but rather its physical status in terms of its fluidity.

Coping with the cold: the cold shock response in the Gram-positive soil bacterium Bacillus subtilis

“…thesis of all four unsaturated FA species so far detected in this bacterium (Weber et al 2001a). Although earlier investigations assigned B. subtilis desaturase activity to a membrane-associated enzyme of the acetyl-CoA-desaturase type (Dunkley et al 1991), it has now become clear that this enzyme is a lipid desaturase .…”

“…As such, it modifies the lipids present in the membrane directly at the time of cold shock, thereby providing a rapid-responding system for the modulation of membrane fluidity. Interestingly, in the absence of exogenous isoleucine sources, deletion of des in a B. subtilis strain JH642 background results in a cold-sensitive growth phenotype, indicating an important role for this enzyme during cold adaptation (Weber et al 2001a). In such a mutant, artificial expression of des in trans does not only cure the observed phenotype but demonstrates that Des possesses cryoprotective properties that significantly increase the cold tolerance of B. subtilis (Weber et al 2001a).…”

“…In such a mutant, artificial expression of des in trans does not only cure the observed phenotype but demonstrates that Des possesses cryoprotective properties that significantly increase the cold tolerance of B. subtilis (Weber et al 2001a). Although it was reported that UFAs are exclusively synthesized upon cold shock (Aguilar et al 1998(Aguilar et al , 1999, recent investigations revealed that in the absence of isoleucine, B. subtilis produces detectable amounts of UFAs even at 37°C (Weber et al 2001a). These findings indicate that our current understanding of the regulation of UFA production is not yet complete and might involve isoleucine itself as a modulator molecule.…”

The Sensitivity of Yeast Mutants to Oleic Acid Implicates the Peroxisome and Other Processes in Membrane Function

“…Mga2p is a key transcription factor that controls expression of Ole1, the sole fatty acyl desaturase in S. cerevisiae responsible for conversion of the saturated fatty acids stearate (C18) and palmitate (C16) to oleate and palmitoleate, respectively (Zhang et al 1999;Chellappa et al 2001). The ratio of saturated to unsaturated fatty acids (UFA/SFA) is known from studies of Bacillus subtilis, for example, to be a key determinant of membrane fluidity (Grau and de Mendoza 1993;Weber et al 2001). Suutari et al (1990), however, showed that the UFA/SFA ratio of Saccharomyces is unaffected by growth temperature.…”

Characterization and Localization of Fluorescent Pseudomonas Cold Shock Protein(s) by Monospecific Polyclonal Antibodies

“…Therefore, during the study the steady-state growth at 4 C transcription increased about 10-fold and led to enhancing the level of protein expression. Weber et al (2001) (29) suggested that cold shock led to chromosome compaction due to a decrease in the transcriptional and translational capacity of the cell. Immunofluorescence electron microscopy confirmed that CSPs were localized around the nucleoid and that the zone of localization increases concomitant with nucleoid compaction.…”