S U M M A R YHalobacterium strains produce a truly extracellular proteinase which degrades gelatine and casein. It has a pH optimum of about 8 and depends upon divalent cations and a high concentration of NaCl or KC1 for activity and stability. Proteolytic enzymes were also found in cell homogenates obtained by ultra sonic treatment. A caseinolytic enzyme, probably different from the extracellular one, is associated with particles which sediment upon ultracentrifugation. A soluble peptidase of lower molecular weight is also present in the extract. Both enzymes are dependent upon divalent cations and a high concentration of NaCl or KCI for activity. In contrast to other halophilic enzymes, the proteolytic enzymes of Halobacterium sdharium are more active in the presence of NaCl than KCl at equimolar concentrations. I N T R O D U C T I O NBacteria of the genus Halobacterium are widely distributed in brines of high salt concentration. They are thus conspicuous in solar evaporation ponds of salt works, where they often become the dominating type of organisms when the salt concentration rises above 25 %. The extremely halophilic bacteria are best cultivated in complex media containing peptones and yeast extract to which at least 15 % (wlv) NaCl has been added. Best growth is obtained in media containing about 25 % salt, and when bacteria are transferred to solutions with a salt concentration of less than about 10 % they lyse rapidly.The unusual properties of halophilic bacteria make them interesting objects of study for both microbiologists and biochemists, and Larsen (1967) summarized the result of a large number of investigations on them. Special methods are often necessary in studies of their metabolism and conventional procedures are unsuitable for the purification and assay of ' halophilic ' enzymes.The extreme halophiles do not generally grow well on carbohydrates but they have a well-developed enzyme apparatus for metabolizing amino acids. In order to utilize the proteins of dead organisms in salt brines the bacteria must form proteolytic enzymes. Gibbons (1957) found that 45 out of 49 tested strains were gelatinolytic, and most of these strains also degraded casein. However, a closer study of the properties of the proteolytic enzymes of such strains has apparently not been made. It is known that the bacteria have an intracellular concentration of NaCl + KCI, which is approximately the same as the NaCl concentration of the growth medium. The halophilic bacteria's enzymes are thus active at salt concentrations which inhibit or even denature many enzymes of non-halophilic organisms. This must be reflected in marked differences in the composition and properties of the protein molecules. Ingram (1947) has

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CeUeuvibrio fulvus and Sporocytaphuga myxococcoidea were grown on different types of cellulose fibres and the degradation was followed by means of light and electron microscopy. The very compact fibres prepared from cotton were degraded slowly by C. julvus. The baoteria penetrated into the lumen of the fibres, accumulated there in large numbers, and degraded the fibres from within. Sporocytophaga myxowccoidee attacked fibres both from the outside and from within by making close contact with the cellulose. Lignin free pulp fibres, which have a very open structure, were rapidly degraded by both kinds of baoteria. Cellwibrio fulvu.9 also degraded these fibres from within. It is concluded that structure of the fibre greatly influences the rate a t which different kinds of cellulolytic bmteria decompose cellulose. PI51

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