Genetic Engineering Applications to Biotechnology in the GenusBacillus

Screening of yeasts from Brazilian Amazon rain forest for extracellular proteinases production

Eighty seven yeast strains representing 34 species isolated from Parahancornia amapa fruit and associated Drosophila flies collected in the Brazilian Amazon rain forest, were screened for proteinase production. Proteolytic activity was tested through casein hydrolysis in solid medium supplemented with 0.5% casein and glucose. Among 23 strains, 18 from genus Candida and 5 from Pichia were caseinolytic and produced proteinases in yeast carbon base liquid medium supplemented with casein 0.01%. The proteolytic activity was tested on pH ranging from 2.0 to 9.0 in correspondence to the pH of the cultures media in which the yeasts were grown. Six highly proteolytic strains: Candida parapsilosis AP153A, C. krusei AP176, C. sorbosa DR215, C. sorbosa AP259, C. valida AP209A and C. sorboxylosa AP287 were selected and the pH optima of production and the proteolytic activity were determined. In general the secretion of proteinase was maximum throughout the exponential and the stationary phases. Greater production occurred in acidic culture and high activity was observed at pH 3.0, 4.0 and 5.0.

High-density cultivation of sporeformers

Sporeformers are sources of a large number of industrially important biological products including enzymes, antibiotics, and bioinsecticides. Cultivation of these microorganisms to high cell densities offers potential for enhancing the rates of formation as well as the concentration of the desired products in the fermentation broths in bioreactors. With this objective, investigations have been carried out involving fed-batch cultivation of Bacillus thuringiensis, which is known to produce an insecticidal crystal protein during sporulation. With appropriate management of aeration and nutrient supply, it was possible to grow the cells to > 50 g DW/l density. Nevertheless, the achievement of high cell density did not enhance the formation of crystal protein in the same proportion as the cell concentration. Further examination of this system suggested a complex interplay of energetic requirements for protein turnover during sporulation. Energy reserve material, poly-beta-hydroxybutyric acid, appeared to be linked to formation of spores and crystal protein during the sporulation phase.

Cloning, nucleotide sequence and expression in Escherichia coli of a lipase gene from Bacillus subtilis 168

The gene coding for an extracellular lipase of Bacillus subtilis 168 was cloned and found to be expressed in Escherichia coli. Enzyme activity measurements showed no fatty acid chain length preference. A set of Tn5 insertions which inactivate the gene were localized and used to initiate its sequencing. The nucleotide sequence was determined on two independent clones expressed in E. coli. In one of these clones, the sequence revealed a frameshift, due to the presence of an additional adenine in the N-terminal region, which caused the interruption of the open reading frame, probably allowing translation to initiate at a second ATG codon. The sequence of the wild-type lip gene from B. subtilis was confirmed on the chromosomal fragment amplified by polymerase chain reaction (PCR). When compared to other lipases sequenced to date, the enzyme described here lacks the conserved pentapeptide Gly-X-Ser-X-Gly supposed to be essential for catalysis. However, alignments of several microbial lipase sequences suggest that the pentapeptide Ala-X-Ser-X-Gly present in the lipase B. subtilis may function as the catalytic site. Homologies were found in the N-terminal protein region with lipases from different Pseudomonas species. The predicted M(r) and isoelectric point for the mature protein are 19,348 and 9.7 respectively.

Mercury resistance determined by a self-transmissible plasmid in Bacillus cereus 5

Inducible mercuric reductase activity in Bacillus cereus 5 was plasmid-encoded. Plasmid analysis revealed three plasmids with molecular masses of 2.6, 5.2 and 130 MDa. A mating system permitted transfer of the resistance determinant among strains of B. cereus and B. thuringiensis. Transfer of mercury resistance from B. cereus 5 to B. cereus 569 and B. thuringiensis occurred during mixed culture incubation on agar surfaces. The 130-MDa plasmid (pGB130) was responsible for transfer; frequencies ranged from 10(-5) to 10(-4). B. cereus 569 transconjugants inheriting pGB130 were also effective donors. High transfer frequencies and the finding that cell-free filtrates of donor cultures were ineffective in mediating transfer suggested mercury-resistance transfer was not phage-mediated. Transfer was also insensitive to DNase activity. Further evidence that pGB130 DNA carried the mercury-resistance determinant was transformation of B. cereus 569 by electroporation with pGB130 DNA isolated from B. cereus 5 and a mercury-resistant B. cereus 569 transconjugant. Mercury-resistant transconjugants and transformants exhibited mercuric reductase activity. Plasmid pGB130 also conferred resistance to phenylmercuric acetate.

Effect of medium composition on the maintenance of a recombinant plasmid in Bacillus subtilis

Recombinant plasmid pCED3 [confers beta-galactosidase production (LacZ+) and kanamycin resistance (Kmr)] in Bacillus subtilis was found to be both segregationally and structurally unstable. Since many solutions to segregational instability are already available, the problem of structural instability was specifically addressed by inclusion of kanamycin in the growth media. Culture instability was found to be highest in complex and defined media supporting high growth rates. Stabilization over the duration of the experiment (40 generations) was achieved by use of a recently developed chemically defined medium supporting a lower growth rate. Slowing down growth by decreasing temperature was much less effective. A major effect of the growth medium appears to be that of decreasing the growth rate advantage held by cells with plasmid deletions over parental cells containing the intact plasmid.

Thermostable enzymes

In general, enzyme thermostability is an intrinsic property, determined by the primary structure of the protein. However, external environmental factors including cations, substrates, co-enzymes, modulators, polyols and proteins often increase enzyme thermostability. With some exceptions, enzymes present in thermophiles are more stable than their mesophilic counterparts. Some organisms produce enzymes with different thermal stability properties when grown at lower and higher temperatures. There are commercial advantages in carrying out enzymic reactions at higher temperatures. Some industrial enzymes exhibit high thermostability. More stable forms of other industrial enzymes are eagerly being sought.