Protozoa stimulate the plant beneficial activity of rhizospheric pseudomonads

Abstract

Aims The functioning of plant-associated bacteria is strongly influenced by their interaction with other organisms. For instance, bacteria upregulate the production of secondary metabolites in presence of protozoa and we hypothesised that this interaction may contribute to plant health.Methods Here, we tested if the effect of beneficial pseudomonads on wheat growth and health is modified by coinoculation with the bacterivorous amoeba Acanthamoeba castellanii. We assessed effects of this co-inoculation in absence and presence of the root pathogen Pythium ultimum. Results In absence of amoebae, bacterial isolates had few beneficial effects and some isolates exacerbated growth inhibition by the pathogen (despite their reported beneficial effects in vitro). Effects on plant growth in absence and presence of the pathogen were negatively correlated. Co-inoculation with amoebae suppressed this relationship, leading to plant growth promotion in absence and reduction of deleterious effects in presence of the pathogen. The positive effect of amoebae in absence of the pathogen could be related to bacterial siderophore production in vitro. Conclusions Our results illustrate the discrepancy between in vitro and in vivo effects of plant beneficial bacteria. Incorporation of other rhizospheric trophic components such as protists may be a key factor to influence the plant-beneficial potential of bacteria in vivo.

Cascading effects from plants to soil microorganisms explain how plant species richness and simulated climate change affect soil multifunctionality

“…We aimed to do so with a full-factorial mesocosm experiment, involving the use of open-top chambers (OTCs) to increase temperature and rainfall shelters to alter precipitation, and manipulated plant species richness to evaluate its direct and indirect (via changes in plant functional structure and soil microbes) effects on soil multifunctionality (Supporting information Figure S1). | 5643 reducing its species richness (Klein, Harte, & Zhao, 2004) and promoting the dominance of plants with more stress-tolerant strategies, ultimately altering the diversity and abundance of soil microbes (e.g., via rhizosphere interactions); (b) altered microbial abundance and/or diversity linked to climate change and shifted plant attributes will regulate soil multifunctionality; (c) mesocosms with the highest diversity will be positively correlated with the highest soil multifunctionality (Maestre et al, 2012); (d) the proportion of soil multifunctionality variance explained will substantially increase when trophic-level complexity is considered (Jing et al, 2015); and (e) protists-rarely studied in this context-are expected to be a key intermediary of the impacts of global change on soil multifunctionality via their role in regulating bacterial populations (Trap et al, 2016;Weidner, Latz, Agaras, Valverde, & Jousset, 2017). Second, we used a variance partitioning analysis to quantify how plants, bacteria and bacterivorous protists alter the impacts of simulated climate change and initial species richness on soil multifunctionality.…”

What drives the assembly of plant-associated protist microbiomes?

“…This again may have important consequences for plant performance, not only because some of these metabolites directly or indirectly influence root growth (Brazelton et al , 2008; Combes-Meynet et al , 2011), but because the same defense compounds ward off microbial competitors, including fungal and bacterial plant pathogens (Arp et al , 2018; Meyer et al , 2009; Ramette et al , 2011; Russell et al , 2014). Accordingly, the resulting communities of rhizosphere bacteria have been shown to express enhanced biocontrol activity, indicating increased reliability of microbiome function (Jousset et al , 2011; Rosenberg et al , 2009; Weidner et al , 2016).…”

Dominant protozoan species in rhizosphere soil over growth of Beta vulgaris L . in Northeast China

“…Protozoa are the higher trophic members of the soil food chain than microorganisms. As the third largest group of soil organism after bacteria and fungi, protozoa have different nutritional types, such as photosynthetic autotroph, humus, and predatory, whose predation behavior not only controls the bacterial community but also promotes nutrient transformation and carbon cycle, and is an important biological regulator of soil biological and biochemical activities [9]. Therefore, the study of protozoan community structure and ecological function forms the basis to elucidate soil fertility and plant growth [10].…”