Analysis of Gold Tolerance in Rhodobacter sphaeroides

Heavy metal pollution is a worldwide problem with many associated health risks, including bone loss, kidney damage, and several forms of cancer. There is a great need of bioremediation of these toxic metals from the environment, as well as implementing a monitoring system to control the spreading pollution. This study focuses on the bioremediation potential of R. sphaeroides in the presence of the toxic gold chloride (AuCl3). A bioinformatics approach is taken to identify all heavy metal related genes within 2,489 bacterial species, identify the genes potentially involved in their bioremediation within the genome of R. sphaeroides. Growth characteristics of the bacterial cells exposed to a range of toxic gold concentrations were analyzed through the growth kinetics and the colony forming units (cfu’s) under aerobic, photosynthetic, and anaerobic growth conditions. The localization of the gold particles within two cellular fractions, cytoplasmic and the plasma membrane, are analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results of this current study reveal the majority (46%) of the heavy metal related genes belong to the species within the Proteobacteria group, and subsequently the αProteobacteria. Upon analysis of the R. sphaeroides genome, 475 heavy metal related genes were identified. Results also reveal the photosynthetic growth condition as best suited for the metal tolerance, allowing a higher survivability under the gold concentrations compared to subsequent growth conditions. Results of the localization revealed the overall accumulation of gold particles, while not different between the cellular fractions, increased at different concentrations of the gold contamination. The results of the photosynthetic localization revealed the accumulation reached the highest very quickly, and an overall shift in localization of the gold particles from an equal distribution to an increase within the membrane fraction at the highest concentrations of gold contamination. Expression profiles of the heavy metal related genes within R. sphaeroides, 369 in total, reveals a total of 46 photosynthetic genes which will be the targets of molecular analysis in the future work.