A survey of microorganisms for thermonuclease production.

A total of 1204 cultures comprising 16 genera were surveyed for production of thermonuclease (TNase) in milk. Cultures other than Staphylococcus capable of TNase production were restricted to two genera, Streptococcus and Bacillus. Nineteen percent of 338 group D streptococci comprising four species (85% of which were Streptococcus faecalis) and 17% of 60 streptococci belonging to other groups produced TNase. Nine percent of 130 Bacillus cultures comprising six species produced the enzyme. On the other hand, 99% of coagulase-positive staphylococci produced TNase and only 18% of the coagulase-negative staphylococci produced the enzyme. The amount of TNase produced by streptococci and bacilli was significantly lower than that produced by coagulase-positive staphylococci. The pH profile of the streptococci and Bacillus TNases was similar to that of the staphylococcal TNase; each enzyme exhibited a minor peak at pH 7.0 and a broad major peak ranging from pH 8.5 to 10. The nuclease produced by coagulase-positive Staphylococcus was more heat stable than the nucleases produced by Streptococcus and Bacillus; there was little loss in activity of the staphylococcal enzyme after 60 min at 100 degrees C, whereas 50% of the activity of the streptococcal and Bacillus nucleases was destroyed in 40-60 min and 60-80 min, respectively.