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FEMS Microbiol Ecol. 2015 Oct;91(10). pii: fiv114. doi: 10.1093/femsec/fiv114. Epub 2015 Sep 20.

Changes in soil bacterial communities and diversity in response to long-term silver exposure.

Author information

1
Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia Istituto di Chimica Agraria e Ambientale, Universitá Cattolica del Sacro Cuore, 29122 Piacenza, Italia sotirios.vasileiadis@unisa.edu.au.
2
Istituto di Microbiologia, Universitá Cattolica del Sacro Cuore, 29122 Piacenza, Italia.
3
Istituto di Chimica Agraria e Ambientale, Universitá Cattolica del Sacro Cuore, 29122 Piacenza, Italia.
4
National Risk Management Research Laboratory, US EPA, Cincinnati, OH 45224, USA.
5
CSIRO Minerals Down Under Flagship, Glen Osmond, SA 5064, Australia.
6
Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia.

Abstract

Silver-induced selective pressure is becoming increasingly important due to the growing use of silver (Ag) as an antimicrobial agent in biomedical and commercial products. With demonstrated links between environmental resistomes and clinical pathogens, it is important to identify microbial profiles related to silver tolerance/resistance. We investigated the effects of ionic Ag stress on soil bacterial communities and identified resistant/persistent bacterial populations. Silver treatments of 50-400 mg Ag kg(-1) soil were established in five soils. Chemical lability measurements using diffusive gradients in thin-film devices confirmed that significant (albeit decreasing) labile Ag concentrations were present throughout the 9-month incubation period. Synchrotron X-ray absorption near edge structure spectroscopy demonstrated that this decreasing lability was due to changes in the Ag speciation to less soluble forms such as Ag(0) and Ag2S. Real-time PCR and Illumina MiSeq screening of 16S rRNA bacterial genes showed β-diversity changes, increasing α-diversity in response to Ag pressure, and immediate and significant reductions in 16S rRNA gene counts with varying degrees of recovery. These effects were more strongly influenced by exposure time than by Ag dose at these rates. Ag-selected dominant OTUs principally resided in known persister taxa (mainly Gram positive), including metal-tolerant bacteria and slow-growing Mycobacteria.

KEYWORDS:

bacterial diversity; selective pressure; silver; soil

PMID:
26391377
DOI:
10.1093/femsec/fiv114
[Indexed for MEDLINE]

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