Content and composition of hopanoids in Zymomonas mobilis under various growth conditions

Abstract

By using a new method for quantification of the different hopanoid derivatives, a total hopanoid content of about 30 mg/g (dry cell weight) was observed in Zymomonas mobiis. This value is the highest reported for bacteria so far. The major hopanoids in Z. mobiis were the ether and glycosidic derivatives of tetrahydroxybacteriohopane, constituting about 41 and 49% of the total hopanoids. Tetrahydroxybacteriohopane itself, diplopterol, and hopene made up about 6, 3, and 1%, respectively. Only minor changes in hopanoid composition were observed with changes in growth conditions. Earlier reports on a correlation between hopanoid content and ethanol concentration in the medium could not be confirmed. Over a wide range of ethanol concentrations (5 to 60 g/liter), growth rates (0.08 to 0.25 h-1), and temperatures (25 to 37C), the molar ratio of hopanoids to phospholipids in the cells amounted to about 0.7. Only at growth rates of >0.30 h-1 did the molar ratio increase to about 1.The gram-negative, obligately fermentative bacterium Zymomonas mobilis is well-known for its high specific rates of ethanol production of up to 5 g of ethanol per g of dry cell weight per h. In continuous culture, Z. mobilis can accumulate up to 6% (wt/vol) ethanol, and in batch culture it can even accumulate up to 13%. Thus, its ethanol tolerance is remarkably high and comparable to that of yeasts (24).Several studies have indicated that ethanol decreases the degree of membrane organization, increases membrane leakage, and influences activities of membrane-associated proteins and transport systems (16,19). In ethanol-tolerant microorganisms, adaptation to ethanol stress involves an increase in the mean chain length of incorporated fatty acids, thereby thickening the hydrophobic membrane core. Often, the proportion of monounsaturated fatty acids (e.g., cisvaccenic acid) also increases (15). The extremely ethanoltolerant Lactobacillus homohiochii even incorporates over 97% unsaturated fatty acids in the membrane when growing in the presence of 10% (wt/vol) ethanol (15). Furthermore, sterols enhance the alcohol endurability of the cell membrane in yeasts, as was demonstrated with anaerobic cultures of Saccharomyces sake, which depended on supplementation with sterol ester to acquire ethanol tolerance (12).For Z. mobilis it was shown that more than 70% of the fatty acids in the phospholipid fraction is cis-vaccenic acid, which appears to be suitable for an ethanol-tolerant microorganism (7, 30). The most striking result, however, was the observation of considerable amounts of neutral hopanoids (6). Several different hopanoid derivatives were detected in Z. mobilis (10) (Fig. 1). Structural similarities to sterols, found in eukaryotic membranes, are apparent (20). Both classes of compounds are amphiphilic and have planar, rigid carbocyclic structures. Moreover, physicochemical studies on model membranes have shown that, like sterols, hopanoids influence membrane fluidity and stability (8,17,18).Recently a new method has been developed which enab...

Hopanoids Are Not Essential for Growth of Streptomyces scabies 87-22

“…Hopanoids may play a more important role in normal growth of the bacteria tested in that study than in S. scabies, or squalene-cyclase inhibitors may have uncharacterized toxic effects on some bacteria. Our data demonstrate that the ⌬hop615-1 and ⌬hop615-7 mutant strains are not compromised in their tolerance to ethanol, which is in agreement with the most recent reports regarding modulation of membrane hopanoid content in response to ethanol in Zymomonas mobilis (10,23). The ⌬hop615-1 and ⌬hop615-7 mutant strains are also not compromised in their tolerance to osmotic stress, high temperature, or low pH under the conditions tested.…”

“…There is conflicting evidence regarding modulation of membrane hopanoid content in the presence of ethanol in bacteria (3,10,23,37). In order to assess the possibility that hopanoids are important for ethanol tolerance in S. scabies, we grew wild-type S. scabies or the ⌬hop615-1 and ⌬hop615-7 mutant strains in liquid MM supplemented with ethanol (1 to 10%, vol/vol).…”

Sugar cane juice fermentation by Zymomonas mobilis CP4 subjected to inhibition by ethanol and high initial concentration of substrate

“…The fermetantion showed a long lag phase and it was incomplete as sugars were not fully metabolised. Cells of microorganisms grown in the presence of ethanol show changes in the lipid composition of the cell plasma membrane (Hermans et al, 1991;Weir & Chase Jr., 1995;Mizoguchi & Hara, 1997). In Z. mobilis there are two possible mechanisms involving lipids to explain the ethanol tolerance.…”

“…In Z. mobilis there are two possible mechanisms involving lipids to explain the ethanol tolerance. In the first mechanism, it is postulated that the high levels of cyclic lipids in the cell membranes protect the bacterium from the toxic effects of ethanol (Hermans et al, 1991). In the second mechanism, it is postulated that the high levels of cis-vaccenic acid in the phospholipids of the bacterial membrane protect the bacterium from ethanol toxicity (Ohta et al, 1981;Moreau et al, 1997).…”

Rare bacteriohopanepolyols as markers for an autotrophic, intra-aerobic methanotroph

“…Tetrafunctionalised BHPs are by far the most common and abundant of all BHPs in both culture and environmental samples . Also in anaerobic bacteria, the BHPs produced seem to be primarily tetrafunctionalised, mainly in the form of BHT (IIa) (Eickhoff et al, 2013;Fischer et al, 2005;Sinninghe Damsté et al, 2004), or with three hydroxyl-groups and an alternative group at the C-35 position such as an amine (IIc), cyclitol ether IIf), glucosamine (IIe), or glycoside (Blumenberg et al, 2006;Eickhoff et al, 2013;Hermans et al, 1991;Llopiz et al, 1992;Neunlist et al, 1985;Rashby et al, 2007). The only exceptions to our knowledge are the reported minor amounts of aminotetrol (IIIc) in some SRB of the genus Desulfovibrio (Blumenberg et al, 2006), and the C 31 and C 30 hopanols produced by periodic acid treatment from Geobacter sulfurreducens (Fischer et al, 2005) that suggest the presence of (small amounts of) penta-and hexafunctionalised BHPs as precursors, although the presence of these structure was not confirmed via LC/MS analysis of samples of the same organism (Eickhoff et al, 2013).…”