Phylogenetic Illustration of Eisenia fetida Associated Vermi-bacteria Involved in Heavy Metals Remediation and Retaining Plant Growth Promoting Traits

Heavy metals contamination in the soil is a major threat to wildlife, the environment, and human health. Microbial remediation is an emerging and promising technology to reduce heavy metals toxicity. Therefore, the present research aimed to isolate and to identify the heavy metals tolerated bacteria from the Eisenia fetida for the first time, and to screen the bacto-remediation capabilities and plant growth promoting traits of vermi-bacterial isolates. Vermi-bacteria was isolated from the gut of E. fetida, identified through staining, culturing, biochemical tests, and ribotyping. Plant growth-promoting traits were also evaluated. Phylogenetic results revealed that isolated Vermi-bacterial strains showed resemblance with Bacillus thuringiensis, Bacillus aryabhattai, Staphylococcus hominis, Bacillus toyonensis, Bacillus cabrialesii, Bacillus tequilensis, Bacillus mojavensis, Bacillus amyloliquefaciens, Bacillus toyonensis, Bacillus anthracis, and Bacillus paranthracis. All identified Vermi-bacterial species are Gram-positive (rod and cocci) in nature, not only indicated the efficient biosorption of lead, cadmium, and chromium but also produce all plant growth stimulating traits such as indole acetic acid (IAA), amylase, protease, lipase, hydrogen cyanide, ammonia, and siderophore production, and also act as a phosphate solubilizers. Bacillus anthracis showed significant production of siderophore (33.0 +/- 0.0 mm), phosphate solubilizing (33.0 +/- 0.0 mm), proteolytic (15.0 +/- 0.0 mm), and lipolytic activities (20.0 +/- 0.0 mm) compared to other vermi-bacterial isolates. Bioaccumulation factor results revealed that Bacillus anthracis showed more accumulation of Cd (12.00 +/- 0.01 ppm), Cr (5.38 +/- 0.01 ppm), and Pb (4.38 +/- 0.01 ppm). Therefore, the current findings showed that all identified vermi-bacteria could be used as potential bactoremediation agents in heavy metals polluted environments and could be used as microbial biofertilizers to enhance crop production in a polluted area.

Automated summary

This study isolated and identified heavy metals-tolerated bacteria from the gut of Eisenia fetida for the first time. The isolated bacteria showed potential bacto-remediation capabilities and plant growth promoting traits. The findings suggest that these vermi-bacteria can be used as potential agents for bioremediation in heavy metals pollution and as microbial biofertilizers to enhance crop production in polluted areas.