Isolation of a variant of Streptococcus faecalis with enhanced barotolerance

Streptococcus faecalis ATCC 9790 was adapted to grow at pressures as high as 1000 atm (1 atm = 101.325 kPa) at 37 degrees C by gradually increasing the growth pressure for agar stab subcultures in steps of 50 atm from 750 atm, the maximum growth pressure for unadapted cultures. A stable variant with enhanced barotolerance designated APR-11 was characterized. Similar variants could be obtained repeatedly from S. faecalis cultures by following the indicated procedure, APR-11 was able to grow in liquid media at pressures some 200 atm greater than the maximum for the parent. It appeared to have a regulatory defect in the arginine dihydrolase system and produced ammonia during glycolysis even in the presence of high concentrations of glucose. The ammonia acted to neutralize metabolic acids and to confer a type of acid tolerance. This acid tolerance may be involved in barotolerance since pressure is known to render S. faecalis hypersensitive to acid conditions. In all, it appeared that pressure can be used as a selection agent for isolation of rare barotolerant variants in normal bacterial populations.