Purification and Characterisation of an Alkaline Protease From Bacillus subtilis Isolated From Tannery Effluent

Abstract

Alkaline proteases from Bacillus species are among the most widely used industrial enzymes, and tanneries, whose effluent is rich in protein, salt, sulfide and chromium, are an obvious place to look for strains that work under harsh conditions. This narrative review asks what the published literature says about isolating Bacillus subtilis from such effluent, purifying its alkaline protease and characterising the enzyme, and how much confidence each step deserves. It draws on work on the subtilisin family, on Bacillus biology, on tannery wastewater and on enzyme methods, and it reports no new experimental data. The recurring pattern is that a clear zone on a plate and a good crude activity are easy to obtain, whereas a defensible purification table, an honest assay description and a kinetic analysis that respects its own assumptions are much rarer. Reported pH and temperature optima depend on substrate, buffer and incubation time, so numbers from different laboratories are seldom comparable. Inhibitor profiles identify the catalytic class only when controls are included, and claims of stability in detergent or in the presence of metals need matching negative controls. The review closes with a short list of what a convincing study of a tannery isolate would report.