Capability of plant growth-promoting bacteria in chromium-contaminated soil after application of composted tannery sludge

The aim of this study was to select bacterial strains with biochemical capability to tolerate high concentration of chromium (Cr) in soils. Plant growth-promoting bacteria (PGPB) were isolated from the root nodules of Phaseolus lunatus and grown in Cr-contaminated soil with the application of composted tannery sludge. Soils were collected from the experimental field with the application of composted tannery sludge (CTS) in five rates: 0, 2.5, 5, 10, and 20 t ha−1 CTS. Bacterial strains were isolated and evaluated for their biochemical capabilities for production of urease, protease, amylase, lipase, catalase, gelatinase, and indole-3-acetic acid, P solubilization, and Cr tolerance. A total of 54 PGPB were isolated from the nodules, being 40%, 37%, 13%, and 10% found in the treatments with 2.5, 5, 10, and 20 t ha−1, respectively. The majority of these isolates presented positive responses for the tests of urease, catalase, and phosphate solubilization, while some isolates were positive for the test of protease, lipase, carboxymethyl cellulose, gelatinase, and amylase. We also observed a decrease in the number of isolates able to tolerate high concentration of Cr. Three strains (UFPI-LCC61, UFPI-LCC64, and UFPI-LCC87) presented high biochemical capability and tolerance to Cr. However, the isolate UFPI-LCC87 showed high biochemical capability and tolerance to the highest concentration of Cr. Our results indicated bacterial strains that present potential to be used in soils contaminated with Cr and also for promoting plant growth.