Margot Kogut

The growth and phospholipid composition of a moderately halophilic bacterium during adaptation to changes in salinity

The effect of a sudden change in NaCl concentration of the medium on the time course of alterations in growth rate and phospholipid composition of the moderately halophilic bacteriumVibrio costicola has been investigated. This organism and other moderate halophiles are known to contain a larger proportion of negatively charged phospholipids in their membranes when grown at higher salt concentrations. We show for the first time that the change in proportion of phosphatidylglycerol, relative to phosphatidylethanolamine, which occurs after a shift from 1M to 3M NaCl, or vice versa, is essentially completed during that period immediately following the salt shift when growth is zero or very slow, and before the cells have adopted the growth rate appropriate to the new salt concentration. It appears, therefore, that the alteration in membrane phospholipid composition may be a necessary physiological response for adaptation to change in salinity.

Isolation of Salt-Sensitive Mutants of the Moderately Halophilic Eubacterium Vibrio costicola

A protocol is described for the first isolation of salt-sensitive mutants from a moderately halophilic eubacterium, namelyVibrio costicola, which normally can grow in up to 3.4M NaCl. Four groups of mutants, which are all unable to grow at high (i.e., 2.5–3.0M) concentrations of NaCl, have been characterized on the basis of their salt and temperature sensitivities. The acquisition of these mutants will be helpful in clarifying the role of membrane lipid changes in haloadaptation.

Salt response of ribosomes of a moderately halophilic bacterium

Extremely halophilic bacteria are well adapted to grow in the high salt concentrations they require [1,2]. Their enzymes, membranes, ribosomes, and presumably other cell structures are able to function well in such environments. Thus, the ribosomes of Halobacterium cutirubrum need ionic conditions similar to those of their internal environment (3 M K ÷ and other salts) for stability and activity [3 -5 ] . The adaptation of moderately halophilic bacteria, which can grow over a wide range of salt concentrations (0.5-3.5 M NaC1, or more) poses special problems. The ability to grow over such ranges is not due to selection of sub-populations but individual cells can grow at all salt concentrations [6]. The internal ionic composition of Vibrio costicola varies when the cells are grown at different NaC1 concentration. The internal ionic concentration is at least as high as the external concentration (D. Shindler, R. Wydro and D. J. Kushner in preparation.) The few studies carried out so far suggest that enzymes formed by such cells when growing at different salt concentrations have the same salt response. This holds for both the NADH oxidase (L. Hochstein, personal commuoication) and the threonine deaminase (D. B. Shindler and D. J. Kushner, unpublished results) of Vibrio costicola and for the extracellular amylase of a moderately halophilic Micrococcus sp [7]. Would ceils growing at one salt concentration produce ribosomes able to function only at that concentration, or would such cells produce ribosomes able to function in a wide range of salt concentrations? As a first step we studied the sedimentation behaviour in different ionic environments of the ribosomes of Vibrio costicola grown in different NaC1 concentrations.