Potential Plant Growth-Promoting Bacteria with Heavy Metal Resistance

Plant growth-promoting (PGP) bacteria commonly have many strategies to cope with heavy metal toxicity. Heavy metal-resistant PGP bacteria can be used to improve the growth of plants in heavy metal contaminated soils. In this study, the soil samples were collected from the lead-zinc mineral deposits in Gümüşhane Province, Turkey. Nine bacterial isolates were obtained on the nutrient agar medium supplemented with 100 mg/mL zinc and lead. All of the isolates were screened in terms of plant growth-promoting characteristics including production of indole-3-acetic acid and siderophore, nitrogen fixation and phosphate solubilisation. Nine bacteria were identified as Bacillus cereus, Bacillus atrophaeus, Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus tropicus, Bacillus subtilis, Bacillus halotolerans, Bacillus vallismortis, and Enterococcus mundtii by classical and 16S rDNA-PCR assays. In addition, these isolates were evaluated for their response to three heavy metals (lead, zinc, copper) dominant in the soil samples and minimal inhibitory concentration (MIC) of the heavy metals was determined with plate dilution method. Consequently, the bacterial isolates in this study possess plant growth-promoting traits and can ameliorate heavy metal contaminated soil. E. mundtii was reported to be found in heavy metal contaminated soil for the first time. This study is the first report about PGP characteristics (IAA production and phosphate solubilisation) of B. vallismortis.