English abstract
Microbial community of the arid region and the potential of their capacity to remediate the carcinogenic hexavalent chromium is considered as an essential issue around the world. Microbes including fungi and bacteria were cultured from chromite (Wadi Fizh) using several media at 30 °C. The isolated microbes were screened for chromium tolerance with media amended with Cr (VI) from 50 to 600 ppm. Isolated Fungi from chromite samples showed more tolerance than bacteria (600 ppm for T. longibrachiatum). Then the Cr (VI) removal capability of the highest tolerating fungi (A.niger and T. longibrachiatum) was studied using batch culture at various pH (3, 5 and 7) and temperature (30, 40 and 50 °C) for optimization. Despite T. longibrachiatum tolerate high level of hexavalent chromium, it did not reduce Cr (VI) in the culture medium. However, A.niger was able to uptake approximately 90 % of Cr (VI). The optimization results showed that the best condition for chromium (VI) removal using A.niger is at pH 7 and 30 °C. The fungus with highly chromium (VI) uptake ability was investigated using bubble column bioreactor. The result showed a decrease of approximately 50 % of chromium (VI) after 3 minutes contact with the media and to 75 % after 12 h of the second load of the chromium (VI). The culture-independent denaturing gradient gel electrophoresis (DGGE) using 341-F and 534-R primers showed that the level of microbial diversity of the three sites was different, with high microbial richness in wadi sediment, moderate in wadi chromite and chromite in the dump has the lowest richness. However, the sequencing result showed that Propionibacterium sp. is common among the three sites. In conclusion, reasonably high uptake ability of indigenous A.niger for Cr (VI) indicates its potential use in bioremediation. However, other parameters should be optimized such as the initial Cr (VI) concentration to increase the removal capacity of the chromium (VI) of this fungus. The DGGE identified microbes could be cultured on their most appropriate conditions and checked for their Cr (VI)
