Propionic Acid Production by a Propionic Acid-Tolerant Strain of Propionibacterium acidipropionici in Batch and Semicontinuous Fermentation.

A propionic acid-tolerant derivative of Propionibacterium acidipropionici P9 was obtained by serially transferring strain P9 through broth that contained increasing amounts of propionic acid. After 1 year of repeated transfers, a strain (designed P200910) capable of growth at higher propionic acid concentrations than P9 was obtained. An increase in the proportion of cellular straight-chain fatty acids and uncoupling of propionic acid production from growth were observed for strain P200910. Growth rate, sugar utilization, and acid production were monitored during batch and semicontinuous fermentations of semidefined medium and during batch fermentation of whey permeate for both strain P200910 and strain P9. The highest propionic acid concentration (47 g/liter) was produced by P200910 in a semicontinuous fermentation. Strain P200910 produced a higher ratio of propionic acid to acetic acid, utilized sugar more efficiently, and produced more propionic acid per gram of biomass than did its parent in all fermentations.

Effect of Proteolytic Enzymes on Transfection and Transformation of Streptococcus lactis Protoplasts.

With both chymotrypsin and mutanolysin used to form protoplasts, consistent transformation frequencies of 10 to 10 transformants and transfectants per mug of DNA were achieved. The procedure was used to transform protoplasts of Streptococcus cremoris CS224 at low frequency (5 transformants per mug of DNA).