PERMEABILIZATION OF STREPTOCOCCUS-THERMOPHILUS AND THE EXPRESSION OF BETA-GALACTOSIDASE

Studies were carried out to determine the efficacy of several permeabilizing agents in inducing high-level expression of beta-galactosidase in Streptococcus thermophilus. Sodium dodecyl sulfate, Triton X-100, sodium deoxycholate, and one commercial bile acid preparation were effective as membrane destabilizing agents allowing lactose influx and hydrolysis by cytoplasmic beta-galactosidase in treated cells. Cells exposed to Oxgall or Triton X-100 displayed 15 times higher levels of beta-galactosidase activity than control cells. Detergent treatment also induced extensive cell death or significant injury to cell populations resulting in long delays before resumption of growth. A permeabilized suspension of S thermophilus corresponding to 10(8)cfu ml(-1) released 87% of glucose available in a 5% lactose solution within 10 min at 50 degrees C.