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Physiological characterization of the APR-11 variant of Streptococcus faecalis ATCC 9790 revealed that the variant has reduced sensitivity to glucose catabolite repression. This reduced sensitivity was indicated by the synthesis of enzymes for catabolism of lactose or arginine in cultures growing at 0.1, 40, or 70 MPa in media with levels of glucose highly repressive for the parent strain. Reduced catabolite repression appeared to be due to reduced activity of the glucose-specific, phosphotransferase system in APR-11 cells. Conversion of pyruvate to lactate or to acetate and ethanol did not appear to be altered in the variant. The APR-11 variant produced a greater final yield of biomass than the parent at all pressures tested, and its barotolerance was especially marked in media with low levels of glucose and high levels of lactose in which derepression of the lactose catabolic system was necessary for full growth. Overall, the greater barotolerance of the APR-11 strain appeared to be due to its enhanced capacity for catabolism related to its reduced sensitivity to catabolite repression by glucose.

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.