Isolation of acetyl esterase mutants of Bacillus subtilis 168

Sustainable Biosynthesis of Esterase Enzymes of Desired Characteristics of Catalysis for Pharmaceutical and Food Industry Employing Specific Strains of Microorganisms

Reactions catalysed by sustainably produced enzymes can contribute to the bioeconomy supporting several industries. Low-value compounds can be transformed into added-value products or high-resolution chemicals could be prepared in reactions catalysed by biocatalyst esterase enzymes. These enzymes can be synthesised by purposely isolated or genetically modified strains of microorganisms. Enzymes belonging to the hydrolase family catalyse the formation and hydrolysis of ester bonds to produce the desired esterified molecule. The synthesis of homo-chiral compounds can be accomplished either by chemical or biocatalytic processes, the latter being preferred with the use of microbial esterases. For varied applications, esterases with high stability and retained activity at lower and higher temperatures have been produced with strains isolated from extreme environments. For sustainable production of enzymes, higher productivity has been achieved by employing fast-growing Escherichia coli after incorporating plasmids of required characteristics from specific isolates. This is a review of the isolated and engineered strains used in the biosynthesis of esterase of the desired property, with the objective of a sustainable supply of enzymes, to produce products of industrial importance contributing to the economy.

Cloning and nucleotide sequencing of a lipase gene from Bacillus subtilis WRRL-B558

A lipase gene from B. subtilis WRRL-B558 was cloned in Escherichia coli JM109 using pBluescript as a vector plasmid. Two methods were combined to screen for the lipase-producing clone. The first was done by overlaying the screening plates with β-naphthylacetate and Fast Blue BB dye. Positive clones were then confirmed by a second method using 1% (v/v) tributyrin agar plates. Positive clones which formed clear zones on the tributyrin agar plates were selected and analysed by restriction mapping, Southern blot hydridization and deletion studies to locate the lipase gene on a 2.2 kb HindIII fragment insert. A subclone harbouring a plasmid with a 0.9 kb DNA fragment between the HindIII and EcoRI sites that still exhibited lipase activity was used for sequencing. The nucleotide sequence showed a single open reading frame which contained 636 nucleotides (212 deduced amino acids). A conserved pentapeptide postulated to be the catalytic site was Ala-X-Ser-X-Gly instead of Gly-X-Ser-X-Gly. The deduced protein was found to have a molecular weight of 21 kDa which was similar to that obtained from the recombinant plasmid as determined by SDS-PAGE. Expression of the Bacillus lipase gene was found to be high in recombinant E. coli.

Production, Purification, and Properties of Extracellular Carboxyl Esterases from Bacillus subtilis NRRL 365

Bacillus subtilis NRRL 365 produced high extracellular carboxyl esterase activity in submerged culture media containing wheat bran, corn steep liquor, and salts. Supplementation of this medium with glucose reduced esterase activity to 37% of that in the unsupplemented control. Esterase activity was purified by ammonium sulfate fractionation, DEAE-Sephadex A-50 ion-exchange chromatography with sodium chloride gradient elution, and preparative polyacrylamide gel electrophoresis. The resultant purified components, esterases I and II, manifested single bands following silver staining of polyacrylamide gel electrophoresis gels and had final specific activities of 80 and 520 U/mg, respectively. Molecular weights for components I and II were 36,000 and 105,000 to 110,000, respectively. Esterases I and II both had a pH optimum of 8.0, with relative activities of 10 and 85%, respectively, at pH 9.0. K m s with p -nitrophenylacetate were 0.91 mM for esterase I and 0.67 mM for esterase II. In general, patterns of enzyme inhibition were similar for both components. Differences were observed in the relative activities of esterases I and II towards p -nitrophenyl esters of acetate, propionate, and butyrate; Activity ratios for components I and II were 100:94:48 and 100:36:23, respectively. The purified components did not hydrolyze long-chain triglycerides and did not manifest proteolytic activity.

Restriction fragments that exert promoter activity during postexponential growth of Bacillus subtilis

Two restriction fragments of Bacillus subtilis DNA were identified which caused the cat-86 gene present on the promoter cloning plasmid pPL703 to be activated predominantly during postexponential growth of host cells. The postexponential increase was observed in both sporulation-positive strains and in a spoOA mutant of B. subtilis. However, the postexponential increase in the cat-86 gene product, chloramphenicol acetyltransferase, was diminished or not observed when the plasmid-containing cells were grown in the presence of excess glucose. The promoter-containing fragment, designated as 33, was mapped to a site on the B. subtilis chromosome adjacent to hisA. The other fragment, 14, mapped to a site adjacent to ctrA. When present on a high-copy vector, both fragments caused a reduction in the sporulation frequency of host cells. Fragment 33 in high copy number conferred on B. subtilis cells three additional phenotypic changes: brown colony color, intracellular inclusions, and, in a protease-deficient mutant, the production of extracellular protease activity. These activities were observed only in postexponential-phase cultures.