Instability of protease production in a rel+/rel- -pair of Bacillus licheniformis and associated morphological and physiological characteristics.

A naturally occurring relaxed/protease-producing (A-type) versus stringent/not protease-producing (B-type) pair of an industrial Bacillus licheniformis has been characterized; either of the two types can convert into the other. Both types can sporulate, grow anaerobically, grow at 56 degrees C and reduce nitrate; morphologically, they can easily be distinguished by cell- and colony-shape. They differ in the ability to use 12 substrates, as determined in API-tests. The two types are remarkably different in their content of extrachromosomal elements (A-type: 2; B-type: 4); furthermore, they differ in their rel-status (A-type: relaxed; B-type: stringent). We propose that the differences in the ability of the two types to use different substrates probably are due to integration/extrusion of the extrachromosomal elements in and out of the chromosome, distorting or restoring a number of genes, together with induction of certain catabolic genes that are under control of the rel-system.