Properties of extracellular proteases from three psychrotolerant Stenotrophomonas maltophilia isolated from Antarctic soil

Three Antarctic psychrotolerant Stenotrophomonas maltophilia were isolated and the characteristics of their extracellular serine proteases were described. The isolates were able to grow at 14 and 34 degrees C, but grew better between 20 and 28 degrees C. The highest protease secretion was reached at 20-24 degrees C. The purified enzyme preparations had maximal activity at 55-60 degrees C and alkaline pH. They showed high pH stability, retaining more than 60% of residual activity after 3 h of incubation at a pH range of 4-12. The thermal stability was slightly lower compared with a commercial mesophilic protease, with 74-79% residual activity after 90 min at 40 degrees C and 50% inactivation at 50 degrees C between 43 and 69 min. These properties suggest that the Antarctic isolates could be adapted to cold by means of synthesising more enzymes with high activity but that the proteases they produce are not truly cold-active, being more similar to mesophilic enzymes.