pH-dependent modulation of alkaline phosphatase activity in Serratia marcescens

Detection of subtle extracellular glucose changes by artificial organelles in protocells

Feedback-controlled detection of subtle changes of extracellular biomolecules as known from cells is also needed in protocells. Artificial organelles, located in protocells, detect the small variation in pH which is triggered by different amounts of invading glucose, converted by glucose-oxidase into gluconic acid. The approach paves the way for using pH fluctuations-detecting artificial organelles in the lumen of protocells.

Phosphate solubilization and acid phosphatase activity of Serratia sp. isolated from mangrove soil of Mahanadi river delta, Odisha, India

Phosphorus is an essential element for all life forms. Phosphate solubilizing bacteria are capable of converting phosphate into a bioavailable form through solubilization and mineralization processes. Hence in the present study a phosphate solubilizing bacterium, PSB-37, was isolated from mangrove soil of the Mahanadi river delta using NBRIP-agar and NBRIP-BPB broth containing tricalcium phosphate as the phosphate source. Based on phenotypic and molecular characterization, the strain was identified as Serratia sp. The maximum phosphate solubilizing activity of the strain was determined to be 44.84 μg/ml, accompanied by a decrease in pH of the growth medium from 7.0 to 3.15. During phosphate solubilization, various organic acids, such as malic acid (237 mg/l), lactic acid (599.5 mg/l) and acetic acid (5.0 mg/l) were also detected in the broth culture through HPLC analysis. Acid phosphatase activity was determined by performing p-nitrophenyl phosphate assay (pNPP) of the bacterial broth culture. Optimum acid phosphatase activity was observed at 48 h of incubation (76.808 U/ml), temperature of 45 °C (77.87 U/ml), an agitation rate of 100 rpm (80.40 U/ml), pH 5.0 (80.66 U/ml) and with glucose as a original carbon source (80.6 U/ml) and ammonium sulphate as a original nitrogen source (80.92 U/ml). Characterization of the partially purified acid phosphatase showed maximum activity at pH 5.0 (85.6 U/ml), temperature of 45 °C (97.87 U/ml) and substrate concentration of 2.5 mg/ml (92.7 U/ml). Hence the present phosphate solubilizing and acid phosphatase production activity of the bacterium may have probable use for future industrial, agricultural and biotechnological application.

Differential expression of thermophilic phosphatases in the wild type and auxotrophic mutant strains of Thermoactinomyces vulgaris

In the wild type strain (stock no. 1227) of Thermoactinomyces vulgaris, as reported earlier [Sinha and Singh (1980) Biochem. J. 190, 457-460], all phosphatase isoenzymes (three alkaline - AlpI, AlpII and AlpIII, and one acidic - Acp) are present. However, the auxotrophic mutants, the strains 1286 (thi(-)), 1279 (nic(-), ura(-)) and 1278 (thi(-), ura(-)) exhibited two alkaline phosphatase isoenzymes (AlpII and AlpIII), but AlpI was lacking. In the strain 1261 (nic(-), thi(-)), only AlpIII was expressed, and AlpI and AlpII isoenzymes were missing. The results suggest that the strains, which require either thiamine (1286 and 1278) or nicotinamide (1279) for their growth, were AlpI(-) mutants; and the strain (1261), which requires both thiamine and nicotinamide for its growth, was AlpI(-)/AlpII(-) double mutant. There was no direct correlation between uracil auxotrophy and the expression of phosphatases. The uniform expression of AlpIII and Acp in all the strains, irrespective of their nutrient requirements, suggest that these constitutive phosphatases are species-specific. The specific activities of the thermophilic acid and alkaline phosphatases were maximum in the wild type strain (1227) of T. vulgaris. The next in phosphatase activity was the strain 1279 (an AlpI(-) mutant), followed by their decrease, in order, in the strains 1286 and 1278 (which were also AlpI(-) mutants); while least activity of these enzymes was observed in the obligate thermophile strain 1261 (AlpI(-)/AlpII(-) double mutant).