Indigenous mercury-resistant bacteria isolated from contaminated soils around artisanal gold processing centers in Sukabumi, Indonesia

Abstract

In Indonesia, the largest mercury pollution comes from artisanal and small-scale gold mining (ASGM), which may cause the distribution of mercury to agricultural land and can be absorbed by food crops. Sukabumi Regency in West Java, well-known as one hotspot of illegal artisanal gold mining and national rice producer, is potentially threatened by mercury pollution. Efforts to remediate mercury contaminated agricultural land can be done by using mercury-reducing bacteria. This research aims to select the most potential indigenous bacteria for mercury remediation. Soil and sludge samples were collected from 2 districts in Sukabumi, where gold processing using mercury is common. Bacteria were selectively isolated from cultured colonies grown in Luria Bertani broth supplemented with HgCl2 30 mg/L. We obtained 27 isolates that belong to 16 species, as identified by API® 20 E and 20 NE (BioMérieux, USA). The growth of each isolate was assessed by measuring the optical density of inoculated LB broth contained HgCl2 30 mg/L for 5 consecutive days. All isolates showed normal growth. The log phase reached its maximum value on the second or third day after inoculation and lag phase afterward. Twelve identified isolates were chosen for evaluation of their resistance to mercury by growing them in Mueller-Hinton agar supplemented with HgCl2 (30 mg/L, 50 mg/L, 100 mg/L, 150 mg/L, and 200 mg/L). Seven isolates were able to grow in media with HgCl2, but only Mer07 survived on HgCl2 150 mg/L.

The growth of mercury-resistant bacterial consortium at different levels of pH, temperature, and C:N ratio

“…Prior to this study, five isolates of mercury-resistant bacteria, namely Exiguobacterium indicum, Enterobacter mori, Acinetobacter junii, Bacillus cereus, and Enterobacter cloaceae, belonging to Gramnegative and aerobic or facultatively anaerobic bacteria, were isolated from mercury-contaminated soils and were tested for their resistant to mercuric chloride (HgCl2) up to the concentration of 100 ppm [17]. Furthermore, the consortium of these bacteria has shown a higher efficiency in mercury reduction tests compared to single strains (unpublished).…”