Phosphomonoesterase activity of the cyanobacterium (blue-green alga) Calothrix parietina

Cellular and extracellular phosphomonoesterase activities were compared in Calothrix parietina D550, a strain whose original environment has been studied in detail. Activity in both fractions became detectable at about the same stage in batch culture. Differences in the influence of environmental factors between the two were slight, suggesting a common origin. The optimum temperatures for cellular and extracellular activities were 40 degrees C and 30 degrees C, respectively, and the upper limits for detectable activity were 80 degrees C and 65 degrees C. The pH optimum for both cellular and extracellular activity was 10.0-10.2. When P-limited cultures were tested with p-nitrophenyl phosphate (pNPP) as substrate, Km values for cellular and extracellular activities were 43 and 33 microM pNPP, respectively. Eleven ions were tested for their influence on activity. In most cases the effect was low or negligible at concentrations likely to be present in nature or freshwater laboratory media. Where obvious effects occurred, these were usually apparent at lower concentrations with extracellular than cellular activity. One mM Ca led to a 40% increase in extracellular activity in comparison with 0.1 mM Ca, but had no effect on cellular activity. However, inorganic phosphate, which had a marked inhibitory effect at concentrations above 10 microM, brought about a similar response with cellular and extracellular activities (approximately 60% decrease with 100 microM).