Effect of growth temperature on the long-chain diols and fatty acids of Thermomicrobium roseum

Abstract

Long-chain 1,2-diols constitute the hydrophobic backbone of membrane lipids (replacing glycerolipids) in the thermophilic eubacterium Thermomkrobium roseum. The effects of incubation temperature on chain length and chain branching of diols and fatty acids were investigated. The maintenance of appropriate membrane fluidity is of particular interest in thermophilic bacteria, as membrane stability has been suggested as a major factor in the ability of microorganisms to live in very hot environments (4, 13).Thermomicrobium roseum is an extremely thermophilic, gram-negative eubacterium (optimal growth temperature of about 70°C) (8). It has an atypical cell wall lacking any significant amount of peptidoglycan (15). The membrane lipids of this unusual organism were investigated, and a series of straight-chain and methyl-branched long-chain 1,2-diols was found (18). The diol-based lipids of T. roseum replace the usual glycerol-based lipids and can be considered the structural equivalent of a glycerol molecule plus one fatty acyl, aldehyde, or alcohol side chain: CH2-R CH-OH CH2-OHStraight-chain and methyl-branched fatty acids were also shown to be present in the membrane lipids of T. roseum (18). With the fatty acid ester-linked to the diol (or possibly, amide linked via a polar head group), the acylated diol could provide the double-chain form typical of glycerol-based lipids.In the present study we undertook to investigate the effect of growth temperature on the diols and fatty acids of T. roseum. T. roseum ATCC 27502 was grown in liquid medium * Corresponding author. 655 (American Type Culture Collection) at pH 8.5. Growth curves were determined in triplicate for each temperature (60, 65, 70, and 75°C), and cells for lipid analysis were harvested from one 2-liter batch in the late log phase. Total lipids were extracted from the wet cell pellet (after centrifugation to recover cells) by a modification of the method of Bligh and Dyer (3).The diols and fatty acids were recovered from acid methanolysis of the total lipids as described previously (10,18). The fatty acid ester distribution was determined by gas chromatography (18) against standards. Diols were analyzed as their alkane derivatives (10) and identified by gas chromatography (18) against alkane standards and against known mixtures of diols converted to alkanes. Diols were 'also analyzed as their acetate derivatives (9).The effect of increased temperature on the distribution of diols and of fatty acids is shown in Tables 1 and 2. The results indicate that T. roseum responds to increased temperatures primarily by decreasing the ratio of branched to straight chains, although there is also a small increase in average chain length with temperature (Table 3).The internal methyl branching on both diols and fatty acids is somewhat unusual, although 10-methylstearic acid

Characterization of novel long-chain 1,2-diols in Thermus species and demonstration that Thermus strains contain both glycerol-linked and diol-linked glycolipids

“…The present study appears to be the first to determine the partial structures of intact diol-containing lipids in bacteria, and it seems likely that these glycosylated acyldiols are functionally equivalent to glycero-glycolipids, with the hydrophobic tail of the diol replacing one of the fatty acyl groups of the latter (22,23). We also show that unlike Thermomicrobium roseum, some strains of the genus Thermus contain a mixture of diol-and glycerol-based glycolipids.…”

“…Long-chain diols have not previously been detected in Thermus species, but Thermomicrobium roseum, a thermophilic member of the green nonsulfur bacteria (GNS) which has an optimum growth temperature of about 70 to 75°C (12,21), has been shown to contain a mixture of straight-chain and branched long-chain 1,2-diols in its polar lipids (22,23). The spectra of the TMS ethers of the diols from the glycolipids of T. scotoductus X-1 and T. filiformis Tok4 A2 were therefore compared with those of authentic 1,2-diols obtained by acid methanolysis of Thermomicrobium roseum biomass.…”

“…Long-chain diols have not thus far been identified in any bacterial species other than Thermomicrobium roseum, in which the polar lipids are apparently exclusively 1,2-diol linked (22,23), and possibly in its relative, the moderate thermophile Chloroflexus sp. (31), although this latter report requires confirmation.…”

“…permethylation that the polar head groups were linked to the C-1 hydroxyl group and the fatty acyl substituents were esterified to the C-2 hydroxyl group (22,23).…”

Reclassification of Sphaerobacter thermophilus from the subclass Sphaerobacteridae in the phylum Actinobacteria to the class Thermomicrobia (emended description) in the phylum Chloroflexi (emended description)

“…Both are thermophilic, obligately aerobic, chemoheterotrophic, catalase-positive, non-motile, non-spore-forming, short irregular-shaped rods with similar DNA G+C content Garrity & Holt, 2001b). The cell membrane of T. roseum contains distinctive long-chain diols instead of the familiar glycerol-based lipids (Pond et al, 1986) and these have been postulated to contribute to membrane stabilization at high temperatures (Pond & Langworthy, 1987). S. thermophilus has not been investigated for its cell membrane composition, but given its relationship to T. roseum and the fact that it is a thermophile, it may also contain diol-based lipids.…”