Improved production of propionic acid by strains of Propionibacterium
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Abstract
A method for semi-continuous fermentation using a propionic acid tolerant mutant of Propionibacterium acidipropionici was developed that increased the yield of propionic acid. This strain was able to grow in medium containing up to 8% propionic acid. Propionic acid yields of approximately 5% were obtained within 5 days of fermentation in a semi-continuous process. Uncoupling of growth and acid production occurred during fermentation with the mutant strain, carbohydrate continued to be metabolized though growth and acid production had ceased;A new method for more efficient production of protoplasts was developed. By growing strain P104 in sodium lactate broth supplemented with 1% threonine and treating these cells with a combination of lysozyme and protease enzymes, osmotically sensitive cells were produced able to regenerate on hypertonic medium to walled cells;Attempts to transfer transposons and plasmid DNA into propionibacteria by polyethylene glycol-induced protoplast transformation, electroporation, and conjugation were made. Antibiotic-resistant cells often appeared during these experiments, but autonomous plasmid DNA was never isolated in recipients. However, DNA hybridization of putative protoplast transformants indicated possible chromosomal integration of the plasmids.