Pyrene effects on methanotroph community and methane oxidation rate, tested by dose–response experiment and resistance and resilience experiment

Abstract

Purpose Methanotrophs are an important group of bacteria that can metabolize methane. Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants and present in all ecosystems. We hypothesize that PAHs may affect methanotrophs and methane oxidation. In this study, we assessed dose-response curves for the inhibition of methane oxidation and methanotrophs diversity by pyrene, and resistance and resilience of soil methane oxidation rate and methanotrophs composition in response to pyrene contamination. Material and methods Methanotrophic bacterial diversity was determined by terminal restriction fragment length polymorphism analysis of the pmoA gene, while methanotrophs composition was assessed by cloning and sequencing of the pmoA gene. Sequences with 98% or more identity were considered as the same operational taxonomic unit (OTU). The pyrene concentration at which methane oxidation decreased by 50%, as compared to the non-spiked control soil (EC 50 ), was determined. Both EC 50 concentration and 500 mgkg −1 of pyrene were applied as disturbances in the resistance and resilience experiment. Resistance and resilience were determined 1 and 40 days, respectively, after spiking pyrene.Results and discussion Methane oxidation rate decreased with increasing pyrene concentrations and the EC 50 value was 22.0 mgkg −1 . Methanotrophic bacterial community diversity decreased in 200 and 500 mgkg −1 pyrene treatments, and methanotroph community structure shifts occurred in 100, 200, and 500 mgkg −1 pyrene treatments. Methane oxidation was neither resistant nor resilient to pyrene disturbance. However, methane oxidation of soil with 22.0 mgkg −1 pyrene disturbance recovered to some extent after 40 days incubation. There were five OTUs identified in the control samples, but the number of OTUs increased 1 day after the addition of 22 mgkg −1 of pyrene. It suggests that a low level of disturbance may increase diversity. Forty days after 500 mgkg −1 of pyrene disturbance, only one OTU belonging to Methylocaldum was detected. The resilience of Methylocaldum to a high level of pyrene could be due to the high genomic GC content, which reduces the frequency of insertion by pyrene into the DNA duplex. In addition, we found that the number of OTUs decreased in all treatments after the 40-day incubation. Conclusions Methane oxidation activity was more sensitive to pyrene than the methanotroph community structure, but could recover under a low level of pyrene. Significant decrease in diversity and shift in species composition occurred only after severe perturbation. A low level of disturbance could increase biodiversity, while a high level of disturbance could decrease it.

Insights into the resistance and resilience of the soil microbial community

“…This was consistent with there being functional redundancy between the species, but with the caveat that apparently unimportant species in a stable environment might have a role in maintaining function in a fluctuating environment, that is, be important for stability (Bell et al, 2005). At high concentrations, diversity was decreased and no recovery was observed (Deng et al, 2011). Changes in species richness are most often considered when investigating the role of biodiversity for eco-system functioning while biodiversity encompasses other components such as evenness (the relative abundance of species).…”

Disturbance Increases Microbial Community Diversity and Production in Marine Sediments

“…The hypothesis was tested previously with in situ data from marine sediment, where depth was used as a proxy for disturbance (Boer et al, 2009), but only a weak relationship was observed. A number of studies have been conducted on soil microorganisms, in which no relationship (Fierer et al, 2003; Wakelin et al, 2010; Deng et al, 2011) or only a negative impact of disturbance has been reported (Kim et al, 2013). Here, the positive relationship was observed both at the beginning of the experiment, when the nutrient load was high, and later, when the organic carbohydrate concentrations were significantly lower.…”

Multilevel ecotoxicity assessment of polycyclic musk in the earthworm Eisenia fetida using traditional and molecular endpoints

“…It is well known that gene expression Fig. 1 The acute lethal response of E. fetida exposed to AHTN (a) and HHCB (b) after 7-day and 14-day exposures in natural soil toxicity test Table 3 The growth rate and reproduction rate (cocoon/worm) of E. fetida after a 28-day exposure to the solvent control and AHTN or HHCB-spiked natural soil can serve as early-response biomarker for chemical exposure, because they can be detected at low concentrations of chemicals and before morphological or reproductive effects become visible (Ryan et al 2005;Deng et al 2011). Therefore, there is a great need to develop gene expression analysis for improving traditional toxicological tests (Zhou et al 2004).…”