Potential of Exopolysaccharides Producing-Lead Tolerant Bacillus Strains for Improving Spinach Growth under Lead Stress

Industrial wastewater is a popular source of irrigation for farming community around the metropolitans due to dissolved nutrients. However, it contains a variety of organic and inorganic pollutants that make it unfit for crop production. Lead (Pb) is among the most toxic heavy metals present in wastewater. Certain bacterial strains have developed resistance against heavy metals which can be used to grow vegetables by utilizing wastewater as irrigation source. Present study was conducted to characterize EPS- producing, Pb-tolerant bacterial strains with multiple plant growth promoting traits for improving spinach growth under wastewater irrigation. Forty bacterial isolates were purified from wastewater and 10 out of them with more Pbresistance under plate and broth assay were screened for their ability to improve growth of spinach seedlings in jar trial using lead nitrate Pb(NO3)(2) as source of lead. Results showed that lead contamination significantly decreased plant growth parameters at all levels when compared with unstressed control plants. Inoculation with Pb-tolerant strains significantly improved shoot length (29.82%), shoot dry weight (28.30%), root length (28.62%) and root dry weight (26.31%) as compared to respective control. The Pb-tolerant bacteria decreased root and shoot lead uptake as compared to control plants. Six isolates i.e. N8, N11, N18, N25, N29 and N35 showing more efficiency to improve spinach growth under axenic conditions were characterized for different plant growth promoting attributes followed by identification through 16S rRNA sequencing. All the tested Pb-tolerant strains i.e. N8, N11, N18, N25, N29 and N29 had multiple plant growth promoting traits. The phylogenic analysis confirmed these strains as Bacillus megaterium (N8), B. safensis (N11), Bacillus sp. (N18), Bacillus sp. (N25), B. megaterium (N29), and B. subtilis (N35). The N11 and N18 proved to be the best strains which not only improved spinach growth but also decreased the Pd uptake by stabilizing it in the root zone. These strains can be a good source of inoculum for growing vegetables by utilizing wastewater as source of irrigation. (C) 2020 Friends Science Publishers