Degradation of amino acids by Lactobacillus casei and some factors influencing deamination of serine.

Lactose is the usual source of energy for multiplication of Lactobacillus casei (Orla-Jensen, Holland) in milk, but when milk is made into cheese the lactose content usually is depleted within a few days. Even then, in such cheese as Cheddar, lactobacilli may continue to increase in numbers until 6 to 12 months after the cheese is made, thus demonstrating the ability of these organisms to utilize some compound(s) other than lactose as a source of energy. The presence of amino-acid deaminases often has been demonstrated in bacteria of different species, but reports on such deaminases in L. casei, the most common lactobacillus in Cheddar cheese, are not available. The present study was carried out to investigate the ability of L. casei to deaminate amino acids, in order to establish these as a possible source of energy for growth of L. casei in Cheddar cheese.