Abstract
Remediation and management of Chromium (Cr) contaminated soils for safe usage has been a serious challenge. The aim of present work was to isolate and identify Cr tolerant bacterial strains and assessing their plant growth promoting potential under controlled conditions. Soil samples were collected from Gujrat District, Pakistan, and analyzed for Cr content and bacteria isolation. In-vitro screening was done for chromium tolerance and plant growth-promoting (PGP) abilities. The tolerant isolates which also exhibited PGP abilities were used as inoculants in germination and pot trial experiment. The isolates A5 and A6, identified as Pseudomonas plecoglossicida and Staphylococci saprophyticus through 16S rRNA gene sequencing, were found to be tolerant up to 700 mg L-1 of Cr (VI). Both were effective in solubilizing phosphate but only A5 (Pseudomonas plecoglossicida) was able to produce indole acetic acid. A5 also increased the percentage of seed germination from 17 to 46% and spinach plant’s biomass by 44% with respect to the control. Keeping in view the results obtained, A5 (Pseudomonas plecoglossicida) appeared as the best species that was able to tolerate Cr stress and promote plant growth. Further, it can be developed as a bio-inoculant for non-food agricultural applications for remediation of Cr contaminated soils.
Highlights
Industrialization, agricultural practices and various anthropogenic activities lead to the build-up of heavy metals in the environment
Analysis for hexavalent chromium via UVVis spectrophotometer revealed that the amount of Cr(VI) in B2 was the highest i.e. 177 mg kg-1
The results showed that many heavy metal tolerant bacteria, like Pseudomonas sp. (A5), Bacillus sp. (A2) and Staphylococci sp. (A6) from this work, were plant growth-promoting as reported earlier by Gadd [22]
Summary
Industrialization, agricultural practices and various anthropogenic activities lead to the build-up of heavy metals in the environment. These heavy metals pose serious threats to terrestrial and aquatic ecosystems. Chromium (Cr) is one of the seventeen chemicals that pose the highest danger to human health according to the United States Environmental Protection Agency (USEPA) [1] It is a transition element which occurs naturally in rocks, plants, animals, soil, gases and in volcanic ash [2]. Cr(III) is considered to be a vital element, for glucose, lipid and protein metabolism in animals in small amounts whereas Cr(VI) is extremely toxic for biological systems [5] It disseminates into soil and water as it is highly soluble, mobile and permeable through biological membranes [6]
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