Studies of polyamine metabolism in obligately alkalophilic Bacillus alcalophilus that grow at pH 11

Bacillus alcalophilus, an obligately alkalophilic bacterium, grow at pH 11 with an intracellular pH greater than 9.5. Polyamines are positively charged at physiological pH, but less than 50% of polyamines will be charged at pH 9.5 and above. In view of the importance of polycationic nature of polyamines in their physiological functions, it is of interest to study the polyamine metabolism in B. alcalophilus, an unusual organism that grow at very high pH. Spermidine is the major polyamine in this organism, accounts for more than 90% of total polyamine. The level of spermidine fluctuates between 10 to 30 nmol per mg protein during growth. In contrast, putrescine and spermine levels stay constant during entire period of growth. No ornithine decarboxylase (DC) activity can be detected in B. alcalophilus under all conditions examined. When (/sup 3/H)arginine was added to the bacterial culture, the distribution of radioactivity in polyamine pool was 3% for putrescine, 94% for spermidine, and 3% for spermine, suggesting the presence of arginine pathway for polyamine biosynthesis. B. alcalophilus appears to possess a polyamine transport system that is Na/sup +/-dependent. Putrescine uptake in B. alcalophilus is sensitive to the inhibition of gramicidine S (10 ..mu..M) and valinomycin (2..mu..M).