Screening and characterization of alkaline protease produced by a pink pigmented facultative methylotrophic (PPFM) strain, MSF 46

Among the various bacterial isolates, the strain MSF 46 isolated from thorn forest soil samples, Tamil Nadu, India, was screened and characterized for its proteolytic activity. While the 16S rRNA sequencing and biochemical characterization revealed that the strain closely resembles Methylobacterium sp., methylotrophy of the strain was confirmed by the sequence homology of mxaF gene with other relative Methylobacterium sp. The alkaline protease was purified to homogeneity using DEAE cellulose ion exchange chromatography, with a 5.2-fold increase in specific activity and 34% recovery. The apparent molecular weight of the enzyme was determined as 40 kDa by SDS–PAGE study. The pH and temperature optima were 9.0 and 50 °C respectively with maximum protease activity of 1164 U/ml. Protease of MSF 46 was active in a broad pH range 7.0–11.0 with a maximum at pH 8.5 and exhibited thermostability at 50 °C. The enzyme activity was inhibited by PMSF but showed stability with Tween 20, Triton X-100 and hydrogen peroxide. Nearly 30% reduction in enzyme activity was observed in the presence of EDTA and DTT. The enzyme was effective in hydrolyzing gelatin, skimmed milk and blood clots and exhibited the potency for dehairing of goat skin and removing blood stain from cotton fabric. Significant morphological changes were observed under scanning electron microscope between cells grown in normal and casein amended medium. This first detailed report on the production of alkaline protease by a PPFM strain appears promising toward development of protocols for mass production, study of the molecular mechanism and other applications.