Effective solubilization and single-step purification of Bacillus licheniformis alpha-amylase from insoluble aggregates

Bacillus sp. as a microbial cell factory: Advancements and future prospects

Bacillus sp. is one of the most distinctive gram-positive bacteria, able to grow efficiently using cheap carbon sources and secrete a variety of useful substances, which are widely used in food, pharmaceutical, agricultural and environmental industries. At the same time, Bacillus sp. is also recognized as a safe genus with a relatively clear genetic background, which is conducive to the industrial production of target metabolites. In this review, we discuss the reasons why Bacillus sp. has been so extensively studied and summarize its advances in systems and synthetic biology, engineering strategies to improve microbial cell properties, and industrial applications in several metabolic engineering applications. Finally, we present the current challenges and possible solutions to provide a reliable basis for Bacillus sp. as a microbial cell factory.

Property Improvement of α-Amylase from Bacillus stearothermophilus by Deletion of Amino Acid Residues Arginine 179 and Glycine 180

To improve the properties of α-amylase from Bacillus stearothermophilus (AmyS), a deletion mutant AmyS∆R179-G180 was constructed by deleting arginine (Arg179) and glycine (Gly180) using site-directed mutagenesis. AmyS and AmyS∆R179-G180 were expressed in Bacillus subtilis and purified by ammonium sulfate precipitation, after which the enzymatic properties were characterized and compared. By deleting amino acids Arg179 and Gly180, the thermostability of α-amylase AmyS∆R179-G180 was enhanced and the half-life at 100 °C significantly increased from 24 to 33 min. In addition, AmyS∆R179-G180 exhibited greater acid resistance and lower calcium requirements to maintain α-amylase activity. The secretory capacity of the recombinant strain was evaluated by fed-batch fermentation in a 7.5-litre fermentor in which high α-amylase activity was obtained. The highest activity reached 3300 U/mL with a high productivity of 45.8 U/(mL·h).

Escherichia coli signal peptidase recognizes and cleaves the signal sequence of α-amylase originating from Bacillus licheniformis

The gene encoding the α-amylase from Bacillus licheniformis was cloned, with and without the native signal sequence, and expressed in Escherichia coli, resulting in the production of the recombinant protein in the cytoplasm as insoluble but enzymatically active aggregates. Expression with a low concentration of the inducer at low temperature resulted in the production of the recombinant protein in soluble form in a significantly higher amount. The protein produced with signal sequence was exported to the extracellular medium, whereas there was no export of the protein produced from the gene without the signal sequence. Similarly, the α-amylase activity in the culture medium increased with time after induction in case of the protein produced with signal sequence. Molecular mass determinations by MALDI-TOF mass spectrometry and N-terminal amino acid sequencing of the purified recombinant α-amylase from the extracellular medium revealed that the native signal peptide was cleaved by E. coli signal peptidase between Ala28 and Ala29. It seems possible that the signal peptide of α-amylase from B. licheniformis can be used for the secretion of other recombinant proteins produced using the E. coli expression system.