Biodiversity of soil bacteria exposed to sub-lethal concentrations of phosphonium-based ionic liquids: Effects of toxicity and biodegradation

Abstract

Little is known about the effect of ionic liquids (ILs) on the structure of soil microbial communities and resulting biodiversity. Therefore, we studied the influence of six trihexyl(tetradecyl)phosphonium ILs (with either bromide or various organic anions) at sublethal concentrations on the structure of microbial community present in an urban park soil in 100-day microcosm experiments. The biodiversity decreased in all samples (Shannon's index decreased from 1.75 down to 0.74 and OTU's number decreased from 1399 down to 965) with the largest decrease observed in the microcosms spiked with ILs where biodegradation extent was higher than 80%. (i.e. [P][Br] and [P][2,4,4]). Despite this general decrease in biodiversity, which can be explained by ecotoxic effect of the ILs, the microbial community in the microcosms was enriched with Gram-negative hydrocarbon-degrading genera e.g. Sphingomonas. It is hypothesized that, in addition to toxicity, the observed decrease in biodiversity and change in the microbial community structure may be explained by the primary biodegradation of the ILs or their metabolites by the mentioned genera, which outcompeted other microorganisms unable to degrade ILs or their metabolites. Thus, the introduction of phosphonium-based ILs into soils at sub-lethal concentrations may result not only in a decrease in biodiversity due to toxic effects, but also in enrichment with ILs-degrading bacteria.

Herbicidal Ionic Liquids Containing the Acetylcholine Cation

“…It should also be noted that the test was carried out with the use of activated sludge microorganisms and that the biodegradability of the studied compounds in agricultural soils may differ . Furthermore, fully synthetic ILs may notably decrease the biodiversity of microbial populations on the example of phosphonium‐based ILs or ammonium‐based ILs, whereas HILs did not significantly impact the overall biodiversity or did not exhibit mutagenic properties . Acetylcholine is well known to not penetrate through lipid membranes, however it usually binds with ion channels present in the cell membrane.…”

Herbicidal Ionic Liquids: A Promising Future for Old Herbicides? Review on Synthesis, Toxicity, Biodegradation, and Efficacy Studies

“… 71 , 100 Their studies established that ionic liquids are persistent in tested soils 71 and change the structure of the microbial community. 100 These results showed a significant loss of biodiversity; Shannon’s index (diversity index) decreased from 1.75 to 0.74 and OTUs (operational taxonomic units) decreased from 1399 down to 965. However, the analyses were carried out at sublethal concentrations, and authors suggest that more tests should be applied on environmentally relevant concentrations.…”

“…Nevertheless, an abundance of hydrocarbon-degrading bacteria such as Sphingomonas was shown to be present in IL-treated soil, which were assumed to degrade ILs or their primary metabolites. 100 To date, these types of tests regarding HILs have been conducted only by Ławniczak et al 43 and Czarny et al 85 Ławniczak et al 43 demonstrated that classic herbicides, dicamba and MCPA, are similar or less effective in weed control in comparison to their HIL counterparts. On the other hand, soils treated with dicamba-based HILs were characterized by different microbial community structure compared to soil treated with commercially available herbicides.…”

Heavy Metals as a Factor Increasing the Functional Genetic Potential of Bacterial Community for Polycyclic Aromatic Hydrocarbon Biodegradation

“…Due to the high ecotoxicity of hydrocarbon compounds and their adverse impact on human health, increasing attention has been paid to the development of remediation technologies of contaminated areas. Among them, biological methods based on the enzymatic potential of microbial consortia to metabolize the xenobiotics are very popular [5][6][7][8][9][10][11]. Bioremediation methods are characterized by low process costs and allow for the complete mineralization of xenobiotics.…”