A Comparison of the Characteristics of Extracellular Protein Secretion by a Gram-Positive and a Gram-Negative Bacterium

Abstract

The background to our present knowledge of the extracellular enzymes of bacteria was established in a review by Pollock (1962) whose own interest was in the inducible formation of penicillinase by Bacillus cereus. At this same time, we developed an interest in a different system in which extracellular enzyme formation appeared not to be inducible and in which there was a massive increase in production after the end of the exponential phase of the growth cycle. Thus, Coleman and Grant (1966) described the characteristics of alpha-amylase formation by an organism of the genus Bacillus obtained as a high alpha-amylase-producing strain of Bacillus subtilis in the presence of different carbon sources. During these early studies, problems were created, inadvertently, and perpetuated due to confusion over nomenclature. The position was clarified by Welker and Campbell (1967) who showed that within the genus Bacillus there were two characteristic patterns of extracellular enzyme formation. Alpha-amylase was formed, for example, at a very low level throughout the growth cycle, in one case, and, in the other, a low level of alpha-amylase was achieved during the exponential phase which increased, massively, in the post-exponential phase of the growth cycle. A more detailed examination showed that organisms which produced these two characteristic patters were distinctly different. The organism known as B. subtilis produced exoenzyme at a low level throughout the growth cycle whilst the organism which produced extracellular protein in greatly increased amounts after the end of exponential growth was shown to be genetically distinct from B. subtilis and was named Bacillus amyloliquefaciens. Welker and Campbell (1967) published these findings nearly twenty years ago but in spite of this attempts are still made to relate data from the two species resulting in misconceptions and misinterpretations. We have not studied B. subtilis in any detail other than to confirm the characteristics claimed by Welker and Campbell (1967) for our strain of B. amyloliquefaciens and B. subtilis 168 (Brown and Coleman, 1975).