Graduate Thesis Or Dissertation
 

Ion and salinity effects on induction and function of galactose permease in an Antarctic psychrophilic marine bacterium

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  • A number of Antarctic marine psychrophilic bacteria were isolated having the ability to grow and accumulate ¹⁴ C-TMG only at temperatures below 20 C. It was shown that galactose rather than lactose was the primary inducer and utilizable substrate for the permease system. Further studies with a Vibrio species (Ant-12), have indicated that there was only one inducible galactose uptake system which differs in inducer and substrate specificity from those found in Escherichia coli. The initial rate of ¹⁴ C-TMG uptake exhibited saturation kinetics when measured as a function of increasing external ¹⁴ C-TMG concentrations. A reciprocal plot of these data yielded an apparent Km value of 4. 8 x 10⁻⁶ M. Phosphorylation was not found to be a prerequisite for uptake and accumulation of ¹⁴CTMG. An exogenous source of energy was required for accumulation of ¹⁴C-TMG, while an exogenous precursor supply of an amino acid, in addition to the inducer, was essential for induction. Electron transport and general metabolic inhibitor studies gave further support that uptake was energy dependent. It was found that a specific Na⁺requiremerit existed for uptake and that this requirement varied quantitatively with the substrate being transported. A relatively higher specific Na⁺ requirement was also evident for induction. Furthermore, Ant-12 was shown to have a specific K⁺ requirement and that the levels of K⁺ required for uptake, growth and induction were the same. At suboptimal salinities, uptake, growth and induction were inhibited more by the generally low nonspecific solute concentration than by a specific ion deficiency. The effect of the nonspecific solute may not be totally osmotic since the solute requirement varied both quantitatively and qualitatively with cellular function. A higher nonspecific solute requirement was found for induction than for growth or uptake, the one least requiring the additional solute. In accordance, increasing salinities supported in the following order: induction > growth > uptake. Salinity-temperature and salinity-nutrient interaction studies have shown salinity to be the primary factor in controlling the pattern of cellular function. Only at near maximum growth temperatures and suboptimal growth salinities was the maximum temperature for growth and induction found to increase with increasing salinities.
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