Microbial α-amylases: a biotechnological perspective

Microbial alkaline proteases: From a bioindustrial viewpoint

As the decade progresses this prediction is rapidly being realized, and microbial enzymes are becoming increasingly important in such diverse fields as medicine, brewing, and timber preservation. The genus Bacillus has played a major role in this development as evidenced by the distribution of the papers read at the Fifth International Fermentation Symposium, 1976 (64). Of 23 papers in the session devoted to "Microbial Enzymes of Industrial Interest" no less than ten were concerned with enzymes from bacilli. Reasons for the predominance of these bacteria in this area of study are several. First, they comprise a group of chemoorganotrophs that can be easily maintained and cultivated and yet are markedly heterogeneous in character. Psychrophiles, mesophiles, and thermophiles, in addition to alkalophilic, neutrophilic, and acidophilic species are well represented. Furthermore, virtually all 48 species of the genus listed in Bergey's Manual ofDeterminative Bacteriology (92) secrete a variety of soluble extracellular enzymes, which reflects the diversity of the parental habitats. Amylases that can liquefy starch under pressure at 11000 (194) and proteases that are stable and active at pH 12.0 (6) are extreme examples of enzyme adaption. This article will attempt to review the recent literature concerned with the characterization and properties of the exoenzymes synthesized by the bacilli and the control and mechanisms of their synthesis. It is restricted to this genus because the commercial importance of extracellular enzymes and academic interest in the process of sporulation have prompted a considerable amount of research into this general area. Nevertheless, in the final section I have attempted to equate our present knowledge of exoenzyme synthesis in procaryotes other than

Extracellular enzyme synthesis in the genus Bacillus.

Expression of the alpha-amylase gene of Bacillus subtilis is controlled at the transcriptional level, and responds to the growth state of the cell as well as the availability of rapidly metabolizable carbon sources. Glucose-mediated repression has previously been shown to involve a site near the transcriptional start-point of the amyE gene. In this study, a transposon insertion mutation was characterized which resulted in loss of glucose repression of amyE gene expression. The gene affected by this mutation, which was localized near 263 degrees on the B. subtilis chromosomal map, was isolated and its DNA sequence was determined. This gene, designated ccpA, exhibited striking homology to repressor genes of the lac and gal repressor family. The ccpA gene was found to be allelic to alsA, previously identified as a regulator of acetoin biosynthesis, and may be involved in catabolite regulation of other systems as well.

Catabolite repression of alpha-amylase gene expression in Bacillus subtilis involves a trans-acting gene product homologous to the Escherichia coli lacl and galR repressors.

Alkaline proteases: A review

SUMMARY: The amounts of three catabolite repressible enzymes, alkaline protease, neutral protease and α-amylase, produced by Bacillus subtilis NRRL-B3411 growing in a chemostat, depended on the growth-limiting substrate. Limiting growth with glucose was advantageous for α-amylase synthesis while nitrogen-limited growth was advantageous for synthesis of the two proteases. Under the conditions used, continuous cultures were unsuitable for large-scale production of the three enzymes since spontaneous mutations to less productive strains occurred in the long term.

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R. J. O'Connor

Papers

Continuous culture studies on the biosynthesis of alkaline protease, neutral protease and -amylase by Bacillus subtilis NRRL-B3411.