Microbes in Toxic Mud
For 125 years the waste water from the sulfidic ore mines of Silver Valley in northern Idaho has drained in to the Coeur d’Alene River. As a result the sediments of the river are heavily enriched with high concentrations of toxic metals such as arsenic, iron, lead, and zinc. Although it is hard to imagine that life might thrive in such conditions a recent study by Dr. Gurdeep Rastogi and colleagues, published in Microbial Ecology, used PhyloChip technology to investigate the diversity of microbes that live within the sediment.
Image Credit: Sharon Lebrun, Dreamstime.com
Dr. Rastogi and his colleagues took sediment cores from the riverbed downstream of the mines, extracted microbial DNA, and then used several techniques to identify the microbes present in the sediment. The use of a bacterial 16S rRNA clone library detected 60 operational taxonomic units (OTUs) with the most common being Proteobacteria (53 clones), followed by Actinobacteria (9 clones) and Bacteriodetes (8 clones). In contrast to these results, the use of PhyloChip identified a total of 1,571 OTUs; again the most common phylum was Proteobacteria (48.5% of total OTUs), followed by Firmicutes (17% of total OUTs) and Actinobacteria (10% of total OTUs). In addition there were 22 OTUs that could not be classified at the phylum level suggesting that there are as yet unclassified microbes living in the river sediments.
Within the highly diverse population of microbes present in the sediment were many bacteria that have adapted to living in such hostile conditions and in some cases may even help in limiting the effects of the contamination. Proteobacteria, such as Pseudomonas and Burkholderia for example, are well known for their ability to survive at extreme pH and also to deal with toxic heavy metals. In addition the PhyloChip data also indicated the presence of Arthrobacter spp. from the phylum Actinobacteria, which are heavy metal resistant, sulfate-reducing bacteria such as Desulfobacterium and Desulfonauticus, Fe(III)-reducing bacteria including Shewanella and Brevibacillus, Fe(II)-oxidizing bacteria such as Leptothrix, as well as ammonia-oxidizing bacteria such as Nitrosospira and Nitrosomonas. Although direct comparisons with uncontaminated river sediment still need to be performed the presence of such a broad community of microbes indicates that heavy-metal contamination may alter but does not necessarily reduce the diversity of microbe populations in river sediment.
Article:
Gurdeep Rastogi, Sutapa Barua, Rajesh K. Sani, and Brent M. Peyton. (2011). Investigation of Microbial Populations in the Extremely Metal-Contaminated Coeur d'Alene River Sediments. Microbial Ecology, 62:1–13.
DOI: 10.1007/s00248-011-9810-2
About the author: Ruth Warre is a freelance scientific writer and editor currently living in Toronto. She writes on a variety of subjects from microbiomes to neuroscience, in a variety of mediums from blogs to peer-reviewed articles.
