Bacteria, Beneficial: Propionibacterium spp. and Acidipropionibacterium spp.

Genomic evidence has led to the division of genus Propionibacterium into Propionibacterium and Acidipropionibacterium. They are pleomorphic rods, anaerobic to aerotolerant, mesophilic, Gram-positive and of high G+C. They produce propionic acid as a major end product from many substrates. P. freudenreichii is used as ripening culture in Swiss-type cheeses, where it produces propionic and acetic acid, CO2 and aroma compounds leading to the characteristic flavor and eyes. They also produce vitamins and other compounds of interest and may be used as probiotics. Genetic tools and genome sequences are now available for both Propionibacterium and Acidipropionibacterium genera, which will improve their applications.