Soil phyllosilicate and iron oxide inhibit the quorum sensing of Chromobacterium violaceum

Abstract

Microorganisms respond to various adverse environmental conditions and regulate different physiological functions by secreting and sensing signal molecules through quorum sensing (QS) systems. Phyllosilicates and iron oxides present in soils and sediments may have substantial impact on bacterial activity and QS due to their unique reactivity and close association with microorganisms. This research explored the effect of goethite, montmorillonite and kaolinite (0.05-2 g L-1) on the growth and QS of a bacterial model, Chromobacterium violaceum. The results showed that kaolinite and goethite caused cellular damage at low mineral concentrations. The capacity for violacein production and biofilm formation of C. violaceum were inhibited by the minerals in the order of kaolinite > goethite > montmorillonite. The possible underlying mechanisms for QS inhibition by different minerals were investigated. Specifically, kaolinite repressed QS function through downregulation the expression of signal molecules synthesis gene cviI. Goethite and montmorillonite interfered with QS by adsorption of extracellular signal molecules. This work provides a better understanding of the interactions between bacteria and minerals and proposed that the inhibition of QS system is an ignored mechanism for bacterial toxicity by phyllosilicates and iron oxides.

Zooming in to acquire micro-reaction: Application of microfluidics on soil microbiome

“…Bacteria can secrete specific chemical signals, such as acylhomoserine lactones (AHLs) (Tecon and Or, 2017;Yang et al, 2020) to the surrounding environment. When these signal molecules reach a threshold concentration, they can stimulate the expression of specific genes that enable bacteria to better adapt to the changing environment and resist adverse conditions.…”

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

“…Transformation, which involves the direct uptake of eARGs by competent bacteria, is an important HGT pathway to transmit antibiotic resistance in soils. ,− The high adsorption affinity of clay particles for extracellular DNA (eDNA) has been regarded to be responsible for the low transformation frequency of ARGs in soils. ,, A variety of soil attributes and environmental factors, such as soil pH, ionic strength, and particle size of minerals, , could affect the adsorption of eDNA to soil, thereby altering bacterial transformation. In addition, the aggregation of eDNA induced by soil biochar or Al 3+ released from montmorillonite suppressed the transformation of ARGs to Escherichia coli. − Except for eDNA adsorption, the transformation process relies largely on the interaction of soil minerals with bacteria or signal biomolecules. − For example, during the exposure to kaolinite and montmorillonite, the transformation of Bacillus subtilis was inhibited via downregulating the expression of competence genes . Metal oxides (e.g., goethite, magnetite, and nano-Al 2 O 3 ) enhanced the transformation of B.…”

“…subtilis and E. coli by increasing the cell membrane permeability and thus facilitated the entry of ARGs into bacterial cells. − Montmorillonite and goethite reduced the activity of signal molecules, acyl-homo-serine lactones, by surface adsorption, which decreased its bioavailability to Chromobacterium violaceum and impacted bacterial biofilm formation and host pathogenesis. ,, Cell competence for transformation is also formed under the regulation of signal molecules . However, it remains elusive whether soil minerals can mediate bacterial transformation by affecting competent signal activity.…”