Abstract
A major problem of the tanning industry is the disposal of chromium-contaminated wastes which have a deleterious effect on the environment. Inductively Coupled Plasma Mass Spectrometer analysis of tannery dumping soils (Riyadh, Saudi Arabia) showed the presence of high concentrations of chromium (268-297 ppm) and strontium (255-435 ppm). 454 pyrosequencing was applied to characterize the bacterial communities in four contaminated sites and a reference site. A total of 5,862 bacterial clones were assembled through 16S rRNA gene clone libraries. Phylogenetic analysis at the species level demonstrated contrasting distributions, interrelationships and shared species in all sites including the reference site. The chromium-contaminated sites were dominated by bacterial phyla Proteobacteria, Bacteroidetes and Firmicutes while other genera such as Chloroflexi, Acidobacteria, Gemmatimonadetes, Cyanobacteria and Nitrospirae were not detected.
The bacterial genera Halomonas, Proteiniphilum, Alkaliphilus and Marinilabiaceae were identified only in the contaminated sites revealing their capability to tolerate and resist chromium toxicity. A vast variation in bacterial species was observed where Halomonas xinjiangensis was found at a considerable percentage in the chromium polluted soils. These findings revealed that long-term chromium stress in the tannery or dumping soil resulted in community shifts towards a dominance of chromium-resistant bacterial populations.