Abstract:
In order to reduce the fermentation time required for the production of fish sauce, halophilic bacteria with proteolytic activity may be added into the fermentor. Thirteen isolates of halophilic bacteria were isolated from a fermentor after a two-month fish sauce fermentation. Of the five isolates which were found to produce both the gelatinase and caseinase enzymes on an agar medium only one isolate (halophilic bacteria number 8) was found to produce caseinase in liquid culture. This bacterial isolate grew well and exhibited high protease in the form of caseinase activity in liquid culture (medium 73) at 25 per cent sodium chloride concentration. The results of the variations in the types and concentrations of carbon and nitrogen sources revealed that halophilic bacteria number 8 required supplementary nitrogen sources in addition to gelatin. When a supplementary nitrogen source such as cas-amino acids or yeast extract or ammonium chloride was added to medium 73 with 0.5 per cent gelatin, the results showed that the availability of ammonium chloride led to a lower extent of growth but the same extent of proteolytic activity when compared with the same concentrations of the other two organic nitrogen sources. These results suggested that ammonium chloride increased the proteolytic activity. After the variations in the types and concentrations of carbon and nitrogen sources, mineral salts, initial pHs, and experimental temperatures it was found that a suitable medium which yielded comparable growth but significantly higher proteolytic activity for the halophilic bacterial isolate number 8 when compared to the control (medium 73) was 1.0 per cent gelatin, 0.05 per cent cas-amino acids, 0.05 per cent ammonium chloride, 25 per cent sodium chloride, 0.5 per cent potassium chloride and 0.02 per cent calcium chloride, pH 7.0, growth temperature 37 ◦C. Glucose was found to yield less growth and proteolytic activity when compared to gelatin. The protease of this bacterium was found to be an alkaline protease which exhibited maximum activity at pH 8.0-9.0. This halophile was tentatively identified as Halobacterium sp. It was rod-shaped with round, transparent and pink colonies. Electron micrographs showed wavy cell wall with cell membrane, nucleoplasm and a striated electron-dense organelle.