Phagotrophic Protists Modulate Copper Resistance of the Bacterial Community in Soil

Abstract

Protist predation is a crucial biotic driver modulating bacterial populations and functional traits. Previous studies using pure cultures have demonstrated that bacteria with copper (Cu) resistance exhibited fitness advantages over Cu-sensitive bacteria under the pressure of protist predation. However, the impact of diverse natural communities of protist grazers on bacterial Cu resistance in natural environments remains unknown. Here, we characterized the communities of phagotrophic protists in long-term Cu-contaminated soils and deciphered their potential ecological impacts on bacterial Cu resistance. Long-term field Cu pollution increased the relative abundances of most of the phagotrophic lineages in Cercozoa and Amoebozoa but reduced the relative abundance of Ciliophora. After accounting for soil properties and Cu pollution, phagotrophs were consistently identified as the most important predictor of the Cu-resistant (CuR) bacterial community. Phagotrophs positively contributed to the abundance of a Cu resistance gene (copA) through influencing the cumulative relative abundance of Cu-resistant and -sensitive ecological clusters. Microcosm experiments further confirmed the promotion effect of protist predation on bacterial Cu resistance. Our results indicate that the selection by protist predation can have a strong impact on the CuR bacterial community, which broadens our understanding of the ecological function of soil phagotrophic protists.

Copper stress shapes the dynamic behavior of amoebae and their associated bacteria

“…This antibacterial mechanism has also been uncovered in protists and vertebrates, which were used to kill the ingested bacteria in phagosomes [ 28 ]. In the predatory relationship of amoebae and bacteria, copper plays an important role in protistan grazing and this predation mechanism creates selective pressure on bacteria to promote the bacterial copper resistance [ 29 , 30 ]. However, some bacteria such as Paraburkholderia persist within the phagosomal vacuole by subverting the antimicrobial mechanisms [ 31 ].…”