Effect of Mg2+ ion in protein secretion by magnesium-resistant strains of Pseudomonas aeruginosa and Vibrio parahaemolyticus isolated from the coastal water of Haldia port

A rapidly growing industrial complex including oil refineries and chemical industries has developed around the coastal area of Haldia port in the district of Midnapore, West Bengal, India. The coastal water is highly polluted with industrial wastes along with petroleum hydrocarbons. The bacteria isolated from the different sites of the coastal waters were Escherichia coli, Alcaligenes, Acinetobacter, Klebsiella spp., Micrococcus spp., Vibrio spp., Pseudomonas aeruginosa and Vibrio parahaemolyticus. The salinity of the water during the time of collection of samples around the port area was 8.2 ppt. Among the isolated organisms, only two isolates, P. aeruginosa and V. parahaemolyticus, showed growth at 300 mM Mg2+ ion concentration. However, a 3 mM Mg2+ concentration was detected in the coastal water whereas other metal ion concentrations were less than 3×10−5 mM. Resistance to Mg2+ (300 mM) was determined by a 5.5-kb plasmid. A large amount of a 40-kDa outer membrane protein, which was highly soluble in 1 M MgCl2, was isolated from both V. parahaemolyticus and P. aeruginosa. The secretion of proteins in the culture supernatant of V. parahaemolyticus was highly increased when the cells were grown in the presence of 300 mM Mg2+, whereas very low secretion was observed in the same concentration of Mg2+ in the case of P. aeruginosa. Mg2+ may act as a specific release factor in protein secretion by V. parahaemolyticus strains.