Effect of NaCl Concentration and Temperature on the Phospholipid and Fatty Acid Compositions of a Moderately Halophilic Bacterium, Pseudomonas halosaccharolytica
A moderately halophilic bacterium, Pseudomonas halosaccharolytica ATCC 29423, can grow over a wide range of NaCl concentrations (0·5–4·25 M), and high concentrations of NaCl enabled the bacterium to grow well at higher temperatures. The addition of glucose to a medium containing 2 M NaCl resulted in an increase in the proportions of glucosylphosphatidylglycerol and diphosphatidylglycerol with a concomitant decrease of phosphatidylglycerol, whereas there was no effect on the level of phosphatidylethanolamine. Increasing the cultivation temperature from a low level to the optimum for growth induced a marked increase in the relative amount of phosphatidyiglycerol with a concomitant decrease of diphosphatidylglycerol, and further elevation of the temperature reversed the relation between the two phospholipids. Phosphatidylethanolamine gradually decreased as the temperature was increased, while the level of glucosylphosphatidylglycerol remained constant. The relative concentrations of C17 and C19 cyclopropanoic fatty acids increased with a concomitant decrease of corresponding unsaturated fatty acids as the growth temperature was increased. It was found that the total amount of negatively charged phospholipids in cells increased with NaCI concentration in the mediuni, from 0·7 times in 0·8 M NaCl medium up to twice with 2 M or more NaCl, compared with that of neutral phospholipid, phosphatidylethanol amine. Phosphatidyiglycerol mainly contributed to the increased amount of negatively charged phospholipids. Furthermore, changes in the molecular species composition of phospholipids with different NaCl concentrations in the medium were observed; a high pro portion of cyclopropanoic fatty acid-containing species, C16–17 C16–19 and C19–19 with a concomitant decrease of corresponding monounsaturated species was seen in cultures containing high NaCl concentrations at any growth phase, suggesting the induction of cyclopropane synthetase by high levels of NaCl.