Cr(VI) resistance and removal by indigenous microorganisms isolated from San Luis River.

CASTRO MF; DELFINI CD; ALMEIDA C; OLSINA R; MARTINEZ MA; VILLEGAS LB

Cordoba

Congreso; XI CONGRESO ARGENTINO DE MICROBIOLOGIA GENERAL 2015; 2015

SAMIGE

Chromium is used in different industrial processes and released into the environments. The removal of toxic Cr(VI) by microorganisms is a promising approach for Cr(VI) pollution remediation. In the present work, Cr(VI) tolerant microorganisms were isolated by sequential enrichment, identified and the Cr(VI) removal also was studied.Because Chorrillos River Basin (San Luis, Argentina) has deteriorated significantly due to the dumping of inadequately treated domestic and industrial effluents, was selected for this study. The site selected for the isolation (33° 19´49.73 "S, 66° 21´41.92" W) showed low organic content, pH between 6,0 - 8,0 and presented 75, 109 628.9, 48.82 and 40 mg kg-1 of chromium, copper, zinc, lead and nickel respectively. From the river sediment sample, enrichment was carried out in the liquid medium EG en g/l: glucose, 10; K2HPO4, 0.25; KH2PO4, 0.125; MgSO4 and 0.1 yeast extract. The selection was carried out by three sequential steps using 50 ppm de Cr(VI) as selection pressure at 180 rpm and 30°C. The capacity to remove Cr(VI) by consortium was estimated by measuring remaining Cr(VI) concentration in the supernatant using colorimetric 1,5-diphenylcarbaxide every 24h. 50% Cr(VI) removal was the criteria selected to continue the next step. After 15 days, a mixed culture in which representatives of Eukaryotic domain (yeasts and filamentous fungi) and a single Prokaryote were found. According to the partial sequence of 26S rRNA gene, yeasts showed identity with Wickerhamomyces and Candida, while the fungus belongs to Trichoderma genus. Based on the 16S rRNA gene sequence, the bacterium was associated with more than 99% identity to Pediococcus spp. A wide variety of bacteria have been reported for reducing Cr(VI) to Cr(III), under aerobic and anaerobic condition. Since, there are very few reports of capacity to remove chromium and other metals by Pediococcus spp. and related genera. Therefore this bacteria was selected for Cr(VI) removal study. The Pediococcus activity against Cr(VI) was checked by determining the minimum inhibitory concentration (MIC) therefore tolerance and growth was evaluated in increasing concentrations of Cr(VI) (25, 50, 75 and 100 ppm) in EG medium for 7 days. Flasks were inoculated to a final concentration of 2 x 107 FCU ml-1 with an active overnight pre-inoculum and incubated at 30 ºC on a rotary shaker at 250 rpm. Interestingly, this isolated in monoculture showed MIC of Cr(VI) was 75 ppm and was able to remove up to 67% ± 0.62 of Cr (VI) in EG with 25 ppm; 45% ± 0.23 in medium with 50 ppm; and 37% ± 0.66 and 31% ±1.61 in media containing 75 and 100 ppm Cr (VI), respectively.Our results show the potential of Pediococcus sp. to achieve removal of Cr(VI) at higher than those reported in the literature, so this isolated presents an interesting potential for the study of tolerance and removal of chromium and other metals, individually such as part of the mixed culture or consortium.