Plant growth promotion potential of heavy metal resistant bacteria from the sewage contaminated coovum river, Chennai, India

Abstract

Rivers contaminated with sewage are the most disturbed ecosystems due to anthropogenic activities such as release of heavy metals, organic pollutants and pharmaceuticals as well as faecal and pathogenic microorganisms, which coexist with the indigenous microbial population. Coovum is such a much polluted river in Chennai city, India. There have been several programs in operation and plan to remediate the Coovum river. In this context, the present study has aimed to explore some of the beneficial bacteria from this polluted river to be used for environmental and horticultural applications. A total of 43 bacteria were isolated from two different water samples collected from Coovum river. Physicochemical parameters were analysed and found the water is not suitable for either drinking purposes or irrigation purposes. As such, the Coovum water also inhibited the germination and reduced growth of tested seeds and seedlings, respectively thus double confirms its unfitness for irrigation purposes. All these 43 bacteria were screened for different plant growth promotion potentials such as production of phytohormones (Indole Acetic Acid-IAA) and phosphate solubilization. They were also characterized for the production of hydrolytic enzymes, heavy metal resistance and antibiotic resistance to characterize their bioremediation potential. While screening for IAA production, 7 strains were found to produce this plant growth promoting hormone. Similarly, 10 strains were able to solubilize phosphate. All the 17 strains were also characterized for their production of lytic enzymes and found only nine strains were able to show amylolytic activity and nine strains showed proteolytic activity. While screening their antagonistic activity against plant pathogenic fungi, one strain has inhibited the mycelia growth of Macrophomina phaseolina and five strains were able to inhibit Alternaria alternata. Three efficient strains, AMET3006, AMET3028 and AMET3030 were able to grow even at 5 μm concentrations of Hg, Cu, Fe, Mn and Cr. Among these, the best performing strain AMET3006 was identified as Pseudomonas sp. Thus, the present study concludes that even in much polluted ecosystem like Coovum river, bacteria were having plant growth promotion activities, bioremediation potential, heavy metal and antibiotic resistance and added advantage of antifungal activity. These bacteria can be employed to bioremediate the contaminated water which can be used for the purpose of irrigating ornamental plants due to their plant growth promotion activities. Further studies on the practical applications of the selected strains will produce more encouraging results which are underway.