Concentration-dependent responses of soil bacterial, fungal and nitrifying communities to silver nano and micron particles

Abstract

The growing use of silver nanoparticles (AgNPs) is likely to result in increased environmental contamination. Although AgNPs have been reported to affect microbial communities in a range of ecosystems, there is still a lack of information concerning the effect of low concentrations of AgNPs on soil microbial community structures and functional groups involved in biogeochemical cycling. In this study, the concentration-dependent effects of AgNPs and silver micron particles (AgMPs) on bacterial and fungal community structures in an agricultural pastureland soil were examined in a microcosm-based experiment using enzyme analysis, molecular fingerprinting, qPCR and amplicon sequencing. Soil enzyme processes were impacted by Ag contamination, with soil dehydrogenase activity reduced by 1 mg kg of AgNPs and AgMPs. Soil urease activity was less susceptible, but was inhibited by ≥ 10 mg kg AgNPs. The significant (P ≤ 0.001) decrease in copy numbers of the amoA gene by 10 mg kg AgNPs indicated that archaea ammonia oxidisers may be more sensitive to AgNP contamination than bacteria. Amplicon sequencing revealed the bacterial phyla Acidobacteria and Verrucomicrobia to be highly sensitive to AgNP contamination. A broad reduction in the relative abundance of Acidobacterial genera was observed, with the exception of the genus Geothrix which increased in response to AgNP and AgMP amendment. Broad tolerance to Ag was observed among the Bacteriodetes, with higher relative abundance of most genera observed in the presence of AgNPs and AgMPs. The proteobacterial genus Dyella was highly tolerant to AgNPs and AgMPs and relative abundance of this genus increased with Ag concentration. Soil fungal community structure responded to both AgNPs and AgMPs, but the nanoparticle had an impact at a lower concentration. This study demonstrates that pastureland soil microbial communities are highly sensitive to AgNP amendment and key functional processes may be disrupted by relatively low levels of contamination.

Impact of silver nanoparticles (AgNP) on soil microbial community depending on functionalization, concentration, exposure time, and soil texture

“…Furthermore, Schlich et al [77] and Samarajeewa et al [86] observed stimulatory effects with ionic and nanoparticulate silver to ammonia-oxidizing bacteria, which could be ascribed to hormone-like responses to low silver concentrations. By contrast, the stimulation of Bacteroidetes due to silver addition was in agreement with previous observations [52,69,70,97,98]. They exhibit silver resistance genes [78].…”

“…The soil microbial community is responsible for several soil ecosystem services, like the recycling of organic matter, the soil fertility and structure, the biogeochemical nutrient cycles, the toxin degradation and the pathogen control [49][50][51][52][53]. Especially bacteria are the main performer of functional processes, which are integral for maintenance of healthy soil environments [54].…”

“…Nevertheless, Ag10-COOH induced both adverse and advantageous effects in view of the investigated individual biological parameters. Here, individual defense strategies [28,69] as well as species dependent toxicological susceptibility [17,52,70] of the biological parameters might be the underlying reasons.…”

Long-term effects of environmentally relevant concentrations of silver nanoparticles on major soil bacterial phyla of a loamy soil

“…The effect strengths were in general higher for Ag + compared to AgNP. Actually, Acidobacteria are known for their AgNP intolerance in soils [ 16 , 17 , 19 , 49 ]. Here, they were significantly stimulated after 1-day exposure to environmentally relevant concentration of 0.01 mg AgNP/kg.…”

“…Moreover, analyses of the soil bacterial community composition after AgNP exposure were focused on phylum level. These revealed an AgNP intolerance by Acido - and Actinobacteria , whereas Proteobacteria and Bacteroidetes seemed to be unaffected or promoted by silver applications [ 16 – 19 ]. This might lead to devastating effects on acidobacterial driven organic carbon transformation [ 20 ] as well as on actinobacterial recycling of refractory biomaterials by decomposition and humus formation in soils [ 21 ].…”