Screening and characterization of heavy metal tolerant rhizobacteria from wild Musa rhizosphere from coal mining area of Changki, Nagaland, India and assessment of their growth promoting potential under Cd/Cu contaminated conditions

Abstract

In soils polluted with heavy metals, plant growth promoting rhizobacteria (PGPR) with heavy metal tolerance can aid plants to adapt to heavy metal contaminated conditions. Heavy metal tolerant rhizobacteria were isolated from Musa rhizosphere growing the Tsurang Riverbank, Nagaland, India, a coal mining area. A total of 26 bacterial isolates/strains were tested for heavy metals and salt tolerance and some growth-promoting traits like IAA, siderophore production and phosphate solubilisation. Of the 26 strains, 7 strains (TSU1, TSU11, TSU12, TSU3, TSU4, TSU7, and TSU8) supported better plant growth. Different isolates displayed variable heavy metal tolerance (30 to 8070 μg/ml). Strains TSU8 and TSU4 exhibited the highest salt tolerance (12 %). Based on the 16S rRNA sequencing, the isolates were identified as TSU3 (Bacillus cereus) (OQ547230), TSU4 (Bacillus safensis) (OQ547231), TSU8 (Bacillus pumilus) (OQ547232), TSU11 (Klebsiella variicola) (OQ947091), TSU12 (Lelliottia amnigena) (OQ947097), TSU7 (Pseudomonas koreensis) (OQ947088) and TSU1 (Serratia marcescens) (OQ726408). A successful consortium of bacterial isolates was formulated and inoculated on Brassica juncea and Helianthus annuus with heavy metal Cd/Cu (150 µgml−1) in the potted soil. This consortium improved growth performance significantly in both fresh and dry weight basis. In B. juncea, enhancement in root length and weight were recorded by 53 and 93 % respectively against control, while, fresh weight of shoot was improved by 72 % on soil adjunct with PGPR and 67 % with PGPR in heavy metal contaminated condition. Similar trend was also registered on dry weight basis. Whereas, PGPR consortia treated H. annuus registered increased shoot and root lengths both fresh and dry weight basis. This consortium with these seven bacterial isolates may contribute to microbe assisted phytoremediation under heavy metal polluted area.