The use of local bacteria is preferred in bioleaching as an environmental-friendly alternative technology in gold mining. In a preliminary study, rhizobacteria were isolated and cultured from three types of hyperaccumulator vegetation from the Ratatotok gold mine, Indonesia, namely Pteris vittata L., Syzygium aromaticum L., and Swietenia mahagoni Jacq. These rhizobacteria still need to be characterised and identified. This study is aimed to cover bacterial phenotypic characterisation, assessment of bacteria resistance to tailing, and identification of bacterial strains the exhibit the highest resistance to tailings. The assessment was carried out across a spectrum of tailing concentrations, selecting the three most robust strains for molecular identification. The process involved genotypic characterisation to determine the species name by analysing the 16S rRNA gene. The results reveal that the phenotypic characteristics of the bacteria isolates vary, but all of them are the indole acetic acid (IAA) hormone producers. The highest IAA producer is the isolate from the rhizosphere of S. aromaticum. Based on the genotypic characterisation test, three most resistant isolates to tailing stress are the following strains Pseudomonas aeruginosa (RTKP1) and Stenotrophomonas geniculata (RTKP2), both from the rhizosphere of P. vittata; as well as Bacillus cereus (RTKS) from the rhizosphere of S. aromaticum. These three strains need to be further tested for their bioleaching capability to recover gold from tailings. Additionally, this study recommends that gold recovery using biological agents can combine the role of hyperaccumulator plants in phytomining and rhizobacteria in bioleaching.

Isatis cappadocica Desv. is a newly found As-hyperaccumulator showing very high remediation efficiency in polluted soils. We studied the effects of arsenic at 0-1400 μM concentrations on seed germination, relative root length, relative shoot height, and root and shoot biomass in young seedlings of I. cappadocica. The seeds were from Iranian arsenic-contaminated mine spoils and from a non-contaminated population. The control for reference was brassica (Descurenia sofia). Germination decreased significantly versus the control with increasing arsenic concentrations. The response to arsenic exposure differed between the I. cappadocica populations and D. sofia. I. cappadocica from mine spoil seeds showed strong resistance to the highest As concentration, with no adverse effects until the 1000 μM dose. Germination from non-mine seeds of I. cappadocica decreased to 89.6% at 1400 μM As. D. sofia germination was completely inhibited at 400 μM As. Relative root length (RRL) and relative shoot height (RSH) decreased with increasing As concentration. Overall, RRL correlated with RSH. Shoot height and root length were more sensitive to arsenic than other endpoints, and might be used as arsenic toxicity indicators. I. cappadocica showed more As tolerance than the reference brassica.