The Characterization of Stenotrophomonas maltophilia Isolated from Marine Sponge Producing Salt Tolerant Proteases

Protease is an important industrial enzyme and salt tolerant protease in which has desirable properties that could enhance its uses not only in industries, but also in agriculture and environmental. Marine organisms usually harbour halophilic microorganisms which produce salt tolerant protease. In this study, salt tolerant protease producing bacteria from marine sponge were isolated and screened on skim milk marine agar supplemented with different NaCl concentrations (1.5 % w/v). Out of 11 isolates, 8 isolates (S1-1, S1-2, S1-3, S2-1, S2-3, S2-4, S2-5 and S2-6) showed clearing zones with ability to digest casein on the skim milk agar. Morphologically, these strains are gram negative bacilli which grow in yellow colonies and were found to be catalase-positive but oxidase-negative. They are also non-lactose fermenter that produce gelatinase but not α-amylase. The ribosomal 16S rRNA sequencing was used to identify each isolate (Acc. number of S1-1 for MT645770, S1-2 for MT645 771, S1-3 for MT645 772, S2-1 MT645 773, S2-3 MT645 774, S2-4 MT645 775, S2-5 MT645 776 and S2-6 MT645 7767). The 16S rRNA sequences showed that these isolates were highly similar to Stenotrophomonas maltophilia (S2-6, 99.87%) and to a related strain Pseudomonas hibiscicola (S1-1, S1-2, S1-3, S2-1, S2-3, S2-4, S2-5 (97.16-99.9 %). Further proteolytic studies were carried out using skim milk agar with 1.0 %, 2.0 %, 3.0 % and 4.o % (w/v) of NaCl concentrations. All isolates were able to hydrolyze casein which produced clear zones surrounding each colony at 1.0 % and 2.0 % (w/v) salt. However, only isolate S1-5 and S2-6 showed proteolytic activities at 3.0 % (w/v) salt but none of them at 4.0 % (w/v). The ability of these isolates to produce protease which active at higher salt may indicate their potential to be the sources for enzyme with useful properties.