Arsenic Redox Potential of Arsenic Respiring Purple Non-Sulfur Bacteria Rhodopseudomonas palustris Isolated from Industrially Contaminated Sites

Arsenic is a ubiquitous toxic metalloid, the concentration of which has reached dangerous levels in many areas of the world due to various anthropogenic activities. Exposure to high levels of arsenic can cause serious health problems including cancer. Bioremediation offers an inexpensive and eco-friendly solution to such problems. Purple non sulfur bacteria are metabolically diverse, facultative anaerobes and produce photopigments under anoxic conditions under incandescent light. In this study, arsenic resistant purple non sulfur bacteria were isolated from industrially contaminated sites. The bacteria were found to resist other metals as well such as nickel, lead, chromium, cobalt, copper and zinc. The bacterial strain showing the best overall results was identified as Rhodopseudomonas palustris strain F1 by 16S rRNA gene sequencing. R. palustris F1, F2, and K3 were able to perform arsenic respiration using sodium citrate and sodium propionate as electron donors under anoxic conditions. Maximum As oxidation was exhibited by the isolates R. palustris F1, K4 and K5, up to 4.31, 3.6 and 2.32 mM, respectively. Highest As(V) reduction was given by the bacterial isolates R. palustris F1, K5, and K4, up to 7.46, 7.15, and 6.38 mM, respectively. R. palustris F1 was also able to reduce As(V) in artificial wastewater. Such bacteria having the ability to bio-transform arsenic via oxidation and reduction under both aerobic and anoxic conditions can find practical applications in bioremediation.