A dormant amoeba species can selectively sense and predate on different soil bacteria

Abstract

Soil protists are the invisible majority of soil eukaryotes, which are essential but often forgotten parts of the soil ecosystem. They play key roles in microbial food webs by predating on other soil microbes. However, it is not clear how dormant soil protists sense, recognize and feed on diverse microbial prey. In this study, we used a soil amoeba, Dictyostelium discoideum, to study selective discrimination and predation of 14 different bacteria. We found that discrimination and sensing of prey in D. discoideum started as early as resting spores. Dictyostelium discoideum had higher hatching rates, formed bigger amoeba plaques and preferred high nutritional value bacteria. The feeding speed of amoeba on various bacteria was constant and was not linked with sensing of prey or bacterial nutritional value. We also found that higher bacterial density decreased predation efficiency, and one species, P. fluorescens, induced a strong density‐dependent inhibition of amoeba spore production. In conclusion, we find that dormant D. discoideum can selectively sense and predate on different soil bacteria, a process that is likely mediated through active amoeba preference as well as bacterial inhibition. This study provides new insights into the role of protists in shaping soil bacterial communities, and future study needs to assess this in natural soil environments.

Symbiont-Induced Phagosome Changes Rather than Extracellular Discrimination Contribute to the Formation of Social Amoeba Farming Symbiosis

“…Consequently, D. discoideum has an instinctive response to feed on bacteria or acquire symbionts from the complex environment. Recent studies indicate an intense preference for Gram-negative compared to Gram-positive bacteria ( 30 ). However, our study showed that all tested Burkholderia bacteria could attract amoebas, but the cells could not distinguish symbiotic and nonsymbiotic Burkholderia bacteria.…”

Soil Amoebae Affect Iron and Chromium Reduction through Preferential Predation between Two Metal-Reducing Bacteria

“…For example, our previous studies found that dormant D. discoideum could selectively sense and prey on different soil bacteria based on their density and nutritional value. 3 In addition, bacterial size and mobility out of the prey spectrum of the predator can avoid being preyed on by amoeba. 55 In this study, D. discoideum showed preference predation for S. decolorationis S12, while it could not feed on B. laterosporus.…”

“…laterosporus, S. decolorationis S12, and a mixture with the same OD value and bacterial suspension volume . The experimental design with four different bacterial densities (OD 600 = 0.2, 0.6, 1.0, and 1.8) provides comprehensive and reliable information about how D.…”

“…To study how resting D. discoideum spores sense and respond to two metal-reducing bacteria at different density levels, we quantified the hatching rate (number of plaques/100 spores) and total spore numbers of D. discoideum amoeba via feeding on B. laterosporus, S. decolorationis S12, and a mixture with the same OD value and bacterial suspension volume. 3 The experimental design with four different bacterial densities (OD 600 = 0.2, 0.6, 1.0, and 1.8) provides comprehensive and reliable information about how D. discoideum senses and responds to two metal-reducing bacteria. One hundred D. discoideum spores were mixed with 200 μL of bacterial suspensions of different OD 600 (0.2, 0.6, 1.0, and 1.8) on non-nutrient agar plates with Page's Amoeba Saline (NNA-PAS plates; 0.142 g Na 2 HPO 4 , 0.136 g KH 2 PO 4 , 4 mg MgSO 4 •7H 2 O, 4 mg CaCl 2 •2H 2 O, 0.12 g NaCl, and 15 g agar per liter) and incubated them at a light incubator (21 °C) for 192 h. NNA-PAS plates were used to eliminate the variability due to bacterial growth.…”

“…Protists are highly diverse and ubiquitous in terrestrial ecosystems and play an essential role in soil nutrient turnover and microbial community dynamics . Protists can increase available ammonia and silicon to improve soil fertility through interactions with other microbes (e.g., predation, parasitism, and mutualism). , More importantly, heterotrophic protists like amoebae prey on bacteria, fungi, other protists, and nematodes and regulate soil microbial community composition, structure, and function . For example, the social amoeba Dictyostelium discoideum impacts the mortality and activity of microbes by sensing, recognizing, and feeding their food microorganisms in soils .…”