Characteristics of protease synthesis in Bacteroides splanchnicus NCTC 10825

Studies to determine the physiological and nutritional characteristics of protease synthesis by Bacteroides splanchnicus NCTC 10825 showed that the proteases were constitutive and cell-associated during exponential growth in batch culture. As growth slowed and the bacteria entered the stationary phase, proteases that had accumulated intracellularly were released into the culture media. In continuous cultures, dilution rate (D)=0.03 h^–1 to D=0.29 h^–1], protease activity was completely cell-bound and maximal during nitrogen-limited growth at high dilution rates. The proteases hydrolysed a relatively restricted range of protein substrates including casein, azocasein and gelatine (comparative maximum rates of hydrolysis were 1.0, 4.1 and 2.7 units mg^–1 protein respectively). B. splanchnicus proteases exhibited arylamidase activities against leucine p-nitroanilide, valylalanine p-nitroanilide and glycylproline p-nitroanilide. Inhibition experiments indicated that the bacterium produced a mixture of serine, thiol and, possibly, metalloproteases. Protease activities were affected by reducing agents and divalent metal ions. Mercaptoethanol at 1 mm was slightly stimulatory; however, dithiortheitol and dithioerythritol (each 10 mm) respectively inhibited protease activities by 91% and 100%. Calcium ions (5 mm) stimulated protease activity by 30%, whereas Mn²⁺ and Mg²⁺ had little or no effect. Protease and arylamidase activities had neutral to alkaline pH optima. Together, these results show that with respect to the types of protease formed and the physiology of the process, B. splanchnicus proteolysis is similar in many respects to that occurring in species belonging to the B. fragilis group. Correspondence to: G. T. Macfarlane