Smectite clay minerals reduce the acute toxicity of quaternary alkylammonium compounds towards potentially pathogenic bacterial taxa present in manure and soil

Abstract

Quaternary alkylammonium compounds (QAACs) are a group of cationic surfactants which are disinfectants with numerous industrial and agricultural applications and frequently released into the environment. One recent hypothesis is that bacteria present in soil will be protected from acute toxic effects of QAACs in the presence of expandable layer silicates due to interlayer sorption. We therefore studied bacterial growth kinetics with high temporal resolution and determined minimal inhibitory concentrations (MICs) of two QAACs, benzyldimethyldodecylammonium chloride (BAC-C12) and didecyldimethylammonium chlorid (DADMAC-C10), for eight strains of different bacterial taxa (Escherichia coli, Acinetobacter, Enterococcus faecium, Enterococcus faecalis, and Pseudomonas fluorescens) in relation to QAAC sorption to smectite and kaolinite. The MICs of BAC-C12 and DADMAC-C10 were in the absence of smectite and kaolinite in the order of 10 to 30 µg mL−1 and 1.0 to 3.5 µg mL−1 for all strains except the more sensitive Acinetobacter strain. For all tested strains and both tested QAACs, the presence of smectite increased apparent MIC values while kaolinite had no effect on MICs. Sorption curves without bacteria showed that smectite sorbed larger amounts of QAACs than kaolinite. Correcting nominal QAAC concentrations employed in toxicity tests for QAAC sorption using the sorption curves explained well the observed shifts in apparent MICs. Transmission electron microscopy (TEM) demonstrated that the interlayer space of smectite expanded from 13.7 ± 1 Å to 19.9 ± 1.5 Å after addition of BAC-C12. This study provides first evidence that low charge 2:1 expandable layer silicates can play an important role for buffering QAAC toxicity in soils.

Genomic plasticity and adaptive capacity of the quaternary alkyl-ammonium compound and copper tolerant Acinetobacter bohemicus strain QAC-21b isolated from pig manure

“…We studied here only one strain and determined MICs for two common QAACs, BAC-C12 and DADMAC-C10. In a recent study we determined the effects of BAC-C12 and DADMAC-C10 exposure of an A. baumannii strain KPC-SM-21 isolated from digested manure (Heyde et al 2020 ; Pulami et al 2021 ). This strain had lower MIC values for the two QAACs (< 5 µg BAC-C12 ml −1 and 5 µg DADMAC-C10 ml −1 ) than detected here for strain QAC-21b.…”

“…The two QAACs, BAC-C12 and didecyldimethylammonium chloride (DADMAC-C10), were used for susceptibility testing of the strain against common biocides present in disinfection solutions used on farms. Minimal inhibitory concentrations (MIC) values were determined by broth microdilution assay following the CLSI guidelines (M100-ED30) as described by Heyde et al ( 2020 ). Following concentration ranges were tested, 0, 3.125, 6.25, 12.5, 25, 50, 100 and 200 µg BAC-C12 mL −1 , and 0, 0.3125, 0.625, 1.25, 2.5, 5, 10 and 20 µg DADMAC-C10 mL −1 .…”

Adsorption of cationic surfactant as a probe of the montmorillonite surface reactivity in the alginate hydrogel composites

“…33 Due to their molecular structure, BACs interact with negatively charged surfaces as MMT. [34][35][36][37][38] The interaction between cationic surfactant and clay minerals such as MMT is well documented but lately most of these studies have focused on the synthesis of organoclays in order to modify clay surface reactivity. [39][40][41] However, the interest of our research is to study these surfactants as contaminants dissolved in water.…”