The effects of temperature and fatty acid structure on lipid metabolism in Bacillus licheniformis

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.

Unsaturated and branched chain-fatty acids in temperature adaptation of Bacillus subtilis and Bacillus megaterium

The effect of growth temperature on the cellular fatty acid profiles of Bacillus subtilis and Bacillus megaterium was studied over a temperature range from 40 to 10 degrees C. As the growth temperature of B. subtilis was reduced, the lower-melting point anteiso-acids increased, while the higher-melting point iso-acids decreased. Consequently the ratio of branched- to straight-chain acids was unaffected by temperature, although changes in the position of fatty acid branching and the degree of unsaturated branched-chain fatty acids occurred. In B. megaterium a more complicated, biphasic behaviour was observed. Saturated, straight-chain and iso-branched acids decreased only from 40 degrees C down to 20-26 degrees C, and anteiso-acids decreased only from 20-26 degrees C to 10 degrees C, while unsaturated acids increased over the whole temperature range studied. Thus, in B. megaterium total branched-chain acids decreased and straight-chain acids increased as temperature decreased. However, the overall cellular content of lower-melting point fatty acids increased with decreasing temperature in both bacilli, and unsaturated fatty acids appeared to be essential components in the adaptation of the microbes to changes in temperatures. Since changes in the relative amounts of branched- and straight-chain fatty acid biosynthesis are known to reflect differences in fatty acid primers, temperature seems to affect not only the activity of the fatty acid desaturases but also the formation or availability of these primers. The results indicate, however, that notable species-specific regulatory features exist in this genus of bacteria.

Temperature-mediated hyperinduction of fatty acid desaturation in pre-existing and newly formed fatty acids synthesized endogenously in Bacillus megaterium

3H-labedeled fatty acids synthesized endogenously by Bacillus megaterium ATCC 14581 growing at 35 degrees C in the presence of L-[G-3H]valine exhibited the same time-course of hyperinduced desaturation following a temperature decrease to 20 degrees C as was observed previously with exogenously supplied 14C-labeled fatty acids. Radioactive fatty acids synthesized in the presence of [U-14C]glucose during hyperinduction at 20 degrees C following a shift-down from 35 degrees C were desaturated at the same relative rate as 14C-labeled fatty acids synthesized previously at 35 degrees C, suggesting that the newly synthesized fatty acids equilibrate with a large portion of the preexisting moieties before becoming susceptible to desaturation.

A rapidly metabolizing pool of phosphatidylglycerol as a precursor of phosphatidylethanolamine and diglyceride in Bacillus megaterium

Pulse-chase experiments in Bacillus megaterium ATCC 14581 with [U-14C]palmitate, L-[U-14C]serine, and [U-14C]glycerol showed that a large pool of phosphatidylglycerol (PG) which exhibited rapid turnover in the phosphate moiety (PGt) underwent very rapid interconversion with the large diglyceride (DG) pool. Kinetics of DG labeling indicated that the fatty acyl and diacylated glycerol moieties of PGt were also utilized as precursors for net DG formation. The [U-14C]glycerol pulse-chase results also confirmed the presence of a second, metabolically stable pool of PG (PGs), which was deduced from [32P]phosphate studies. The other major phospholipid, phosphatidylethanolamine (PE), exhibited pronounced lags relative to PG and DG in 14C-fatty acid, [14C]glycerol, and [32P]phosphate incorporation, but not for incorporation of L-[U-14C]serine into the ethanolamine group of PE or into the serine moiety of the small phosphatidylserine (PS) pool. Furthermore, initial rates of L-[U-14C]serine incorporation into the serine and ethanolamine moieties of PS and PE were unaffected by cerulenin. The results provided compelling in vivo evidence that de novo PGt, PS, and PE synthesis in this organism proceed for the most part sequentially in the order PGt yields PS yields PE rather than via branching pathways from a common intermediate and that the phosphatidyl moiety in PS and PE is derived largely from the corresponding moiety in PGt, whereas the DG pool indirectly provides an additional source for this conversion by way of the facile PGt in equilibrium or formed from DG interconversion.

Spin-labeling studies on the lipids of psychrophilic, psychrotrophic, and mesophilic clostridia

Spin-labeling studies were conducted to elucidate the viscosity and phase transition temperatures of lipids isolated from psychrophilic, psychrotrophic, and mesophilic clostridia. Electron spin resonance spectroscopy indicated that the lipids, for all the growth temperatures tested, were in a fluid state and from 13 to 24 C higher than the corresponding lipid transition temperatures. When the organisms were grown at different temperatures, a psychrotropic and two mesophilic clostridia were shown to be able to adjust their lipid-phase transition temperature to the growth temperature. A psychrophilic Clostridium strain, when grown at different temperatures, synthesized lipids that had the same phase transition temperature. It is suggested that this lack of growth temperature-inducible regulation of lipid-phase transition temperature may be a molecular determinant for the psychrophily of this organism. It is proposed that the growth temperature range of an organism is dependent upon the ability of the organism to regulate its lipid fluidity within a specific range.