SUMMARY: strain W50 was grown in batch and continuous culture on complex medium with haemin. In batch culture, cell-bound levels of trypsin-like protease (EC, alkaline phosphatase (EC and -acetyl-β-glucosaminidase (EC increased during the exponential phase of growth. These enzyme activities were also detected in extracellular vesicles and in extracellular soluble forms in the supernatant fluid, but in lower amounts per unit biomass compared to cell-bound levels. In continuous culture, at high relative growth rates (0.7-0.9 μ), the highest proportions of enzyme activities were cell-bound. In contrast, at low relative growth rates (0.1-0.2 μ), highest enzyme levels were detected in the extracellular vesicle fraction. Levels of extracellular soluble enzymes were always low compared to cell-bound or extracellular vesicle levels, but were highest at low relative growth rates. All three enzymes appeared to be relatively stable in their soluble forms. Vesicle production appeared to be associated with actively growing cells but was influenced by growth rate. The results are consistent with the hypothesis that cell-bound “periplasmic” enzymes are encapsulated into vesicles which are subsequently released by the cells. Therefore, levels of total extracellular enzyme (extracellular vesicle plus extracellular soluble) may depend on the rate of vesicle formation superimposed on the rates of production of “periplasmic” enzymes in the cell.


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