Plant growth promoting properties of Halobacillus sp. and Halomonas sp. in presence of salinity and heavy metals

Salinity and heavy metal stress are challenging problems in agriculture. Here we report the plant growth promoting ability of three moderate halophiles, Halobacillus sp. ADN1, Halomonas sp. MAN5, and Halobacillus sp. MAN6, in presence of both salinity and heavy metal stress. Halobacillus sp. ADN1, Halomonas sp. MAN5, and Halobacillus sp. MAN6 can tolerate 25, 21, and 29% NaCl, respectively and grow in presence of 1 mM cobalt, cadmium, and nickel and 0.04 mM mercury and 0.03 mM silver. Halobacillus sp. ADN1, Halomonas sp. MAN5, and Halobacillus sp. MAN6 produced 152.5, 95.3, and 167.3 mu g/ml indole acetic acid (IAA) and could solubilize 61, 53, and 75 parts per million (ppm) phosphate, respectively in the presence of 15% NaCl. The production of IAA and solubilization of phosphate was well retained in the presence of salinity and heavy metals like 1 mM cadmium, 0.7 mM nickel, 0.04 mM mercury, and 0.03 mM silver. Besides, the strains showed amylase and protease activities and could produce hydrogen cyanide and ammonia in presence of salinity and heavy metals. A mixture of three strains enhanced the root growth of Sesuvium portulacastrum under saline and heavy metal stress, where the root length increased nearly 4.5 +/- 0.6 times and root dry weight increased 5.4 +/- 0.5 times as compared to control. These strains can thus be useful in microbial assisted phytoremediation of polluted saline soils.