Microbial Predators Research Articles

The yeast Wickerhamomyces anomalus acts as a predator of the olive anthracnose-causing fungi, Colletotrichum nymphaeae, C. godetiae, and C. gloeosporioides.

Olive tree anthracnose is caused by infection with Colletotrichum fungi, which in Portugal are mostly C. nymphaeae, C. godetiae, and C. gloeosporioides s.s. Severe economic losses are caused by this disease that would benefit from a greener and more efficient alternative to the present agrochemical methods. Yeasts are serious candidates for pre-harvest/in field biocontrol of fungal infections. This work identified the yeast Wickerhamomyces anomalus as a strong antagonizer of the three fungi and studied in vitro this ability and its associated mechanisms. Antagonism was shown to not depend on the secretion of volatile compounds (VOCs), or siderophores or any other agar-diffusible compound, including hydrolytic enzymes. Rather, it occurred mostly in a cell-to-cell contact dependent manner. This was devised through detailed microscopic assessment of yeast-fungus cocultures. This showed that W. anomalus antagonism of the three Colletotrichum proceeded through (i) the adhesion of yeast cells to the phytopathogen hyphae, (ii) the secretion of a viscous extracellular matrix, and (iii) the emptying of the hyphae. Yeasts ultimately putatively feed on hyphal contents, which is supported by light microscopy observation of MB and PI co-culture-stained samples. Accordingly, numerous W. anomalus cells were observed packing inside C. godetiae emptied hyphae. This behaviour can be considered microbial predation and classified as necrotrophic mycoparasitism, more explicitly in the case of C. godetiae. The results support the prospect of future application of W. anomalus as a living biofungicide/BCA in the preharvest control of olive anthracnose.

Amoebozoan testate amoebae illuminate the diversity of heterotrophs and the complexity of ecosystems throughout geological time

Heterotrophic protists are vital in Earth's ecosystems, influencing carbon and nutrient cycles and occupying key positions in food webs as microbial predators. Fossils and molecular data suggest the emergence of predatory microeukaryotes and the transition to a eukaryote-rich marine environment by 800 million years ago (Ma). Neoproterozoic vase-shaped microfossils (VSMs) linked to Arcellinida testate amoebae represent the oldest evidence of heterotrophic microeukaryotes. This study explores the phylogenetic relationship and divergence times of modern Arcellinida and related taxa using a relaxed molecular clock approach. We estimate the origin of nodes leading to extant members of the Arcellinida Order to have happened during the latest Mesoproterozoic and Neoproterozoic (1054 to 661 Ma), while the divergence of extant infraorders postdates the Silurian. Our results demonstrate that at least one major heterotrophic eukaryote lineage originated during the Neoproterozoic. A putative radiation of eukaryotic groups (e.g., Arcellinida) during the early-Neoproterozoic sustained by favorable ecological and environmental conditions may have contributed to eukaryotic life endurance during the Cryogenian severe ice ages. Moreover, we infer that Arcellinida most likely already inhabited terrestrial habitats during the Neoproterozoic, coexisting with terrestrial Fungi and green algae, before land plant radiation. The most recent extant Arcellinida groups diverged during the Silurian Period, alongside other taxa within Fungi and flowering plants. These findings shed light on heterotrophic microeukaryotes' evolutionary history and ecological significance in Earth's ecosystems, using testate amoebae as a proxy.

Trophic regulation of soil microbial biomass under nitrogen enrichment: A global meta‐analysis

Abstract Eutrophication, including nitrogen (N) enrichment, can affect soil microbial communities through changes in trophic interactions. However, a knowledge gap still exists about how plant resources (‘bottom‐up effects’) and microbial predators (‘top‐down effects’) regulate the impacts of N enrichment on microbial biomass at the global scale. To address this knowledge gap, we conducted a global meta‐analysis using 2885 paired observations from 217 publications to evaluate the regulatory effects of plant biomass and soil nematodes on soil microbial biomass under N enrichment across terrestrial ecosystems. We found that the effects of N enrichment on soil microbial biomass varied strongly across ecosystems. N enrichment decreased the soil microbial biomass of natural grasslands and forests due to soil acidification and the subsequent losses of predatory and microbivorous nematodes stimulating microbial growth. By contrast, N enrichment increased the microbial biomass of managed croplands mainly via increasing plant biomass production. Across diverse ecosystems, the short‐term N enrichment (experimental duration ≤5 years) could reduce microbial biomass via decreasing nematode abundance, whereas the long‐term N enrichment (experimental duration >5 years) mainly promoted microbial biomass via increasing plant biomass. These findings highlight the critical roles of microbial predators and plant input in shaping microbial responses to N enrichment, which are highly dependent on ecosystem type and the period of N enrichment. Earth system models that predict soil microbial biomass and their linkages to soil functioning should consider the variations in plant biomass and soil nematodes under future scenarios of N deposition. Read the free Plain Language Summary for this article on the Journal blog.

Microbial eukaryotic predation pressure and biomass at deep-sea hydrothermal vents.

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers and hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured microbial eukaryotic cell abundance and predation pressure in low-temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show cell abundances and grazing rates higher than those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between the protistan grazing rate, prey cell abundance, and temperature of end-member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. Our results show substantial protistan biomass at hydrothermally fueled microbial food webs, and when coupled with improved grazing estimates, suggest an important contribution of grazers to the local carbon export and supply of nutrient resources to the deep ocean.

The genetic basis of predation by myxobacteria.

Myxobacteria (phylum Myxococcota) are abundant and virtually ubiquitous microbial predators. Facultatively multicellular organisms, they are able to form multicellular fruiting bodies and swarm across surfaces, cooperatively hunting for prey. Myxobacterial communities are able to kill a wide range of prey microbes, assimilating their biomass to fuel population growth. Their mechanism of predation is exobiotic - hydrolytic enzymes and toxic metabolites are secreted into the extracellular environment, killing and digesting prey cells from without. However, recent observations of single-cell predation and contact-dependent prey killing challenge the dogma of myxobacterial predation being obligately cooperative. Regardless of their predatory mechanisms, myxobacteria have a broad prey range, which includes Gram-negative bacteria, Gram-positive bacteria and fungi. Pangenome analyses have shown that their extremely large genomes are mainly composed of accessory genes, which are not shared by all members of their species. It seems that the diversity of accessory genes in different strains provides the breadth of activity required to prey upon such a smorgasbord of microbes, and also explains the considerable strain-to-strain variation in predatory efficiency against specific prey. After providing a short introduction to general features of myxobacterial biology which are relevant to predation, this review brings together a rapidly growing body of work into the molecular mechanisms and genetic basis of predation, presenting a summary of current knowledge, highlighting trends in research and suggesting strategies by which we can potentially exploit myxobacterial predation in the future.

Metabolic implications for predatory and parasitic bacterial lineages in activated sludge wastewater treatment systems

Deciphering unclear microbial interactions is key to improving biological wastewater treatment processes. Microbial predation and parasitism in wastewater treatment ecosystems are unexplored survival strategies that have long been known and have recently attracted attention because these interspecies interactions may contribute to the reduction of excess sludge. Here, microbial community profiling of 600 activated sludge samples taken from six industrial and one municipal wastewater treatment processes (WWTPs) was conducted. To identify the shared lineages in the WWTPs, the shared microbial constituents were defined as the family level taxa that had ≥ 0.1% average relative abundance and detected in all processes. The microbial community analysis assigned 106 families as the shared microbial constituents in the WWTPs. Correlation analysis showed that 98 of the 106 shared families were significantly correlated with total carbon (TC) and/or total nitrogen (TN) concentrations, suggesting that they may contribute to wastewater remediation. Most possible predatory or parasitic bacteria belonging to the phyla Bdellovibrionota, Myxococcota, and Candidatus Patescibacteria were found to be the shared families and negatively correlated with TC/TN; thus, they were frequently present in the WWTPs and could be involved in the removal of carbon/nitrogen derived from cell components. Shotgun metagenome-resolved metabolic reconstructions indicated that gene homologs associated with predation or parasitism are conserved in the Bdellovibrionota, Myxococcota, and Ca. Patescibacteria genomes (e.g., host interaction (hit) locus, Tad-like secretion complexes, and type IV pilus assembly proteins). This study provides insights into the complex microbial interactions potentially linked to the reduction of excess sludge biomass in these processes.

Entomopathogen-based biopesticides: insights into unraveling their potential in insect pest management.

Global food security is a critical challenge to fulfill the demands of an exponentially growing population. To date, growers rely on chemicals; the broad-spectrum application of synthetic molecules leads to environmental contamination, resistance development, residual toxicity, pest resurgence, and a detrimental effect on human health and cattle. Crop production needs to be improved considering environmental and human health concerns to ensure food security. Furthermore, economically important crops are prone to attack by insect pests, causing considerable yield losses. Microbes are an eco-friendly, versatile alternative, and a potential candidate for combatting destructive pests below the economic injury level and improving the plant's health and productivity. Several microbial pathogens, including parasites, predators, parasitoids, pollinators, and many beneficial microorganisms, possess toxic properties against target organisms but do not cause harm to the non-target organisms. Entomopathogens (ENMs) have great potential for pest suppression due to their remarkable properties. Bacteria are host-specific, but fungi have a broader host range and can be significantly affected by both soil-dwelling and terrestrial insect pests. Virulent pathogens cause mortality in target insect pests known as ENMs and can penetrate through natural openings, ingestions, and integuments to cause a possible effect on target insect pests. The objective of using ENMs is to sustain productivity, improve environmental health, reduce pesticides, and conserve natural resources. Moreover, research is ongoing to discover other possible aspects, especially exploring potential ENMs. Therefore, there is a need for identification, isolation, and bioformulation to overcome the existing issues. This study is mainly focused on the status of bio-formulations, pathogenicity, their mode of action, and the potential application of different types of microbial formulations for sustainable pest management.

Predation in a Microbial World: Mechanisms and Trade-Offs of Flagellate Foraging.

Heterotrophic nanoflagellates are the main consumers of bacteria and picophytoplankton in the ocean and thus play a key role in ocean biogeochemistry. They are found in all major branches of the eukaryotic tree of life but are united by all being equipped with one or a few flagella that they use to generate a feeding current. These microbial predators are faced with the challenges that viscosity at this small scale impedes predator-prey contact and that their foraging activity disturbs the ambient water and thus attracts their own flow-sensing predators. Here, I describe some of the diverse adaptations of the flagellum to produce sufficient force to overcome viscosity and of the flagellar arrangement to minimize fluid disturbances, and thus of the various solutions to optimize the foraging-predation risk trade-off. I demonstrate how insights into this trade-off can be used to develop robust trait-based models of microbial food webs.

Bdellovibrio predation cycle characterized at nanometre-scale resolution with cryo-electron tomography.

Bdellovibrio bacteriovorus is a microbial predator that offers promise as a living antibiotic for its ability to kill Gram-negative bacteria, including human pathogens. Even after six decades of study, fundamental details of its predation cycle remain mysterious. Here we used cryo-electron tomography to comprehensively image the lifecycle of B. bacteriovorus at nanometre-scale resolution. With high-resolution images of predation in a native (hydrated, unstained) state, we discover several surprising features of the process, including macromolecular complexes involved in prey attachment/invasion and a flexible portal structure lining a hole in the prey peptidoglycan that tightly seals the prey outer membrane around the predator during entry. Unexpectedly, we find that B. bacteriovorus does not shed its flagellum during invasion, but rather resorbs it into its periplasm for degradation. Finally, following growth and division in the bdelloplast, we observe a transient and extensive ribosomal lattice on the condensed B. bacteriovorus nucleoid.

Self-demise of soft rot bacteria by activation of microbial predators by pectin-based carriers.

Soft rot pectobacteria (SRP) are phytopathogens of the genera Pectobacterium and Dickeya that cause soft rots on a wide range of crops and ornamental plants. SRP produce plant cell wall degrading enzymes (PCWDEs), including pectinases. Bdellovibrio and like organisms are bacterial predators that can prey on a variety of Gram-negative species, including SRP. In this research, a low methoxyl pectin (LMP)-based immobilization system for B. bacteriovorus is established. It takes advantage that pectin residues induce PCWDE secretion by the pathogens, bringing upon the release of the encapsulated predators. Three commercial LMPs differing in the degree of esterification (DE) and amidation (DA) were tested as potential carriers, by examining their effect on SRP growth, enzymes secretion and substrate breakdown. A clear advantage was observed for pectin 5 CS with the lowest DE and DA content. The degradation of 5 CS pectin-based carriers was further optimized by reducing cross-linker and pectin concentration, by adding gelatin and by dehydration. This resulted in SRP-induced disintegration of the carrier within 72 h. The released encapsulated predator caused a large decrease in SRP population while its own significantly increased, demonstrating the efficiency of this system in which the pathogen brings about its own demise.

Metabolic influence of core ciliates within the rumen microbiome

Protozoa comprise a major fraction of the microbial biomass in the rumen microbiome, of which the entodiniomorphs (order: Entodiniomorphida) and holotrichs (order: Vestibuliferida) are consistently observed to be dominant across a diverse genetic and geographical range of ruminant hosts. Despite the apparent core role that protozoal species exert, their major biological and metabolic contributions to rumen function remain largely undescribed in vivo. Here, we have leveraged (meta)genome-centric metaproteomes from rumen fluid samples originating from both cattle and goats fed diets with varying inclusion levels of lipids and starch, to detail the specific metabolic niches that protozoa occupy in the context of their microbial co-habitants. Initial proteome estimations via total protein counts and label-free quantification highlight that entodiniomorph species Entodinium and Epidinium as well as the holotrichs Dasytricha and Isotricha comprise an extensive fraction of the total rumen metaproteome. Proteomic detection of protozoal metabolism such as hydrogenases (Dasytricha, Isotricha, Epidinium, Enoploplastron), carbohydrate-active enzymes (Epidinium, Diplodinium, Enoploplastron, Polyplastron), microbial predation (Entodinium) and volatile fatty acid production (Entodinium and Epidinium) was observed at increased levels in high methane-emitting animals. Despite certain protozoal species having well-established reputations for digesting starch, they were unexpectedly less detectable in low methane emitting-animals fed high starch diets, which were instead dominated by propionate/succinate-producing bacterial populations suspected of being resistant to predation irrespective of host. Finally, we reaffirmed our abovementioned observations in geographically independent datasets, thus illuminating the substantial metabolic influence that under-explored eukaryotic populations have in the rumen, with greater implications for both digestion and methane metabolism.

Active predation, phylogenetic diversity, and global prevalence of myxobacteria in wastewater treatment plants

The operation of modern wastewater treatment plants (WWTPs) is driven by activated sludge microbiota, a complex assemblage of trophically interacting microorganisms. Microbial predation is crucial to fundamental understanding of how biological interactions drive microbiome structuring and functioning of WWTPs. However, predatory bacteria have received little attention regarding their diversity, activity, and ecological function in activated sludge, limiting the exploitation of food web interactions for wastewater microbiome engineering. Here, by using rRNA-stable isotope probing of activated sludge microbiota with 13C-labeled prey bacteria, we uncovered diverse as-yet-uncultivated putative predatory bacteria that actively incorporated 13C-biomass. Myxobacteria, especially Haliangium and the mle1-27 clade, were found as the dominant active predators, refreshing conventional views based on a few predatory isolates of Bdellovibrionota from WWTPs. The identified predatory bacteria showed more selective predation on prey compared with the protists dominated by ciliates, providing in situ evidence for inter-domain predation behavior divergence in activated sludge. Putative predatory bacteria were tracked over a two-year microbiome monitoring effort at a local WWTP, revealing the predominance of Myxococcota (6.5 ± 1.3%) over Bdellovibrionota (1.0 ± 0.2%) lineages. Phylogenetic analysis unveiled highly diverse myxobacteria inhabiting activated sludge and suggested a habitat filtering effect in global WWTPs. Further mining of a global activated sludge microbiome dataset revealed the prevalence of Myxococcota (5.4 ± 0.1%) species and potential impacts of myxobacterial predation on process performance. Collectively, our findings provided unique insights into the predating activity, diversity, and prevalence of Myxococcota species in activated sludge, highlighting their links with wastewater treatment processes via trophic regulation of enteric and functional bacteria.

The Effect of Long-Term Agricultural Use on the Bacterial Microbiota of Chernozems of the Forest-Steppe Zone

The structure of soil microbial communities and the factors that control it are still poorly understood and cause ongoing interest. The diversity of soil bacteria reflects the diversity of existing ecological niches and trophic connections between them and with other components of the ecosystem. The presence of certain taxa with their own characteristic properties depends on the specific environmental conditions. Analysis of the composition of soil microbiota in various physicochemical conditions allows identify landmarks for understanding the principles by which it is formed. Of particular interest in this regard are the features of cultivated fertile soils that assist agricultural production. In this paper, we have assessed the occurrence of representatives of different families of bacteria in arable and nonarable chernozems of three subtypes. The methodology of 16S microbial profiling was used. The general features of the taxonomic structure of bacterial communities of chernozem remain similar, with a high occurrence of the families Sphingomonadaceae, Xanthobacteraceae, Rubrobacteraceae and Chitinophagaceae. Notably, Gemmatimonadaceae, one of the most commonly occurring families, is approximately twice as represented in arable soils as in nonarable ones. Differences between subtypes of chernozem and between arable and nonarable areas concerned different sets of bacterial families. Among others, the occurrence of representatives of families characterized by nitrogen fixation, nitrite oxidation and reduction, ethanol oxidation, biodegradation and microbial predation is touched upon. The obtained results raise the question of the factors limiting the number of certain groups of bacteria in various soil conditions and so limiting their contribution to the properties of the ecosystem.

Localized coevolution between microbial predator and prey alters community-wide gene expression and ecosystem function

Closely interacting microbial species pairs (e.g., predator and prey) can become coadapted via reciprocal natural selection. A fundamental challenge in evolutionary ecology is to untangle how coevolution in small species groups affects and is affected by biotic interactions in diverse communities. We conducted an experiment with a synthetic 30-species bacterial community where we experimentally manipulated the coevolutionary history of a ciliate predator and one bacterial prey species from the community. Altering the coevolutionary history of the focal prey species had little effect on community structure or carrying capacity in the presence or absence of the coevolved predator. However, community metabolic potential (represented by per-cell ATP concentration) was significantly higher in the presence of both the coevolved focal predator and prey. This ecosystem-level response was mirrored by community-wide transcriptional shifts that resulted in the differential regulation of nutrient acquisition and surface colonization pathways across multiple bacterial species. Our findings show that the disruption of localized coevolution between species pairs can reverberate through community-wide transcriptional networks even while community composition remains largely unchanged. We propose that these altered expression patterns may signal forthcoming evolutionary and ecological change.

Dam construction alters planktonic microbial predator‒prey communities in the urban reaches of the Yangtze River

While dam construction supports social and economic development, changes in hydraulic conditions can also affect natural aquatic ecosystems, especially microbial ecosystems. The compositional and functional traits of multi-trophic microbiota can be altered by dam construction, which may result in changes in aquatic predator–prey interactions. To understand this process, we performed a large-scale sampling campaign in the urban reaches of the dam-impacted Yangtze River (1 995 km) and obtained 211 metagenomic datasets and water quality data. We first compared the compositional traits of planktonic microbial communities upstream, downstream, and in a dam reservoir. Results showed that Bacteroidetes (R-strategy) bacteria were more likely to survive upstream, whilst the reservoir and downstream regions were more conducive to the survival of K-strategy bacteria such as Actinobacteria. Eukaryotic predators tended to be enriched upstream, whilst phototrophs tended to be enriched in the reservoir and downstream regions. Based on bipartite networks, we inferred that the potential microbial predator–prey interactions gradually and significantly decreased from upstream to the downstream and dam regions, affecting 56% of keystone microbial species. Remarkably, functional analysis showed that the abundance of the photosynthetic gene psbO was higher in the reservoir and downstream regions, whilst the abundance of the KEGG carbohydrate metabolic pathway was higher upstream. These results indicate that dam construction in the Yangtze River induced planktonic microbial ecosystem transformation from detritus-based food webs to autotroph-based food webs.

Effect of the entomopathogenic fungus, Lecanicillium lecanii, on the biology and predation rate of the anthocorid predatory bug, Blaptostethus pallescens, feeding on the flower thrips, Frankliniella schultzei Trybom (Thysanoptera: Thripidae)

BackgroundThe flower thrips, Frankliniella schultzei Trybom (Thysanoptera: Thripidae) is a notorious pest that attacks the plants of economic importance. The anthocorid bug Blaptostethus pallescens Poppius (Heteroptera: Anthocoridae) is a predator of thrips in field crops and greenhouses. Another biocontrol agent, the entomopathogenic fungi (EPF) Lecanicillium lecanii (Zimm.) (Hypocreales: Cordycipitaceae), has been effectively used in management of various insect pests. With the aim to develop an effective combination of biocontrol agents like microbial and insect predator for the management of the serious pest F. schultzei, the present studies were carried out on development, predation rate and prey preferences of the predator B. pallescens provided with the EPF (ICAR-NBAIR Vl-8)-treated thrips under laboratory conditions.ResultsThe predator, B. pallescens, could complete its life cycle on treated thrips. The nymphal duration of bugs fed on treated thrips was higher (25.25 ± 0.13 days). The Vl-8 strain did not show any negative effect on hatchability of eggs (83% hatchability in treatment; 86% in control). However, the longevity was comparatively less in bugs fed on treated thrips than that of control group The fecundity of the treated group was found to be reduced to one half of the control group. The rate of daily feeding potential of bugs on treated thrips was less (7.29 ± 0.15) than the untreated thrips (12.54 ± 0.1) throughout their lifetime. Moreover, when the F1 generation from both parents line fed on treated and untreated thrips allowed to feed on Corcyra cephalonica eggs, it did not show any difference in terms of nymphal duration which revealed that the fungi did not affect the F1 generation. When choice was given between treated and untreated thrips to different instars of this predatory bug, all the instars including adult significantly preferred the untreated thrips. However, nymphs and adult bugs were found to encounter both the treated and untreated thrips. No mortality was observed in any stage of the predator.ConclusionThis study shows that the effect of L. lecanii (ICAR-NBAIR Vl-8) on B. pallescens is not harmful. However, further field studies are required to evaluate their combined effect against this pest.

Microbial predators form a new supergroup of eukaryotes.

Molecular phylogenetics of microbial eukaryotes has reshaped the tree of life by establishing broad taxonomic divisions, termed supergroups, that supersede the traditional kingdoms of animals, fungi and plants, and encompass a much greater breadth of eukaryotic diversity1. The vast majority of newly discovered species fall into a small number of known supergroups. Recently, however, a handful of species with no clear relationship to other supergroups have been described2-4, raising questions about the nature and degree of undiscovered diversity, and exposing the limitations of strictly molecular-based exploration. Here we report ten previously undescribed strains of microbial predators isolated through culture that collectively form a diverse new supergroup of eukaryotes, termed Provora. The Provora supergroup is genetically, morphologically and behaviourally distinct from other eukaryotes, and comprises two divergent clades of predators-Nebulidia and Nibbleridia-that are superficially similar to each other, but differ fundamentally in ultrastructure, behaviour and gene content. These predators are globally distributed in marine and freshwater environments, but are numerically rare and have consequently been overlooked by molecular-diversity surveys. In the age of high-throughput analyses, investigation of eukaryotic diversity through culture remains indispensable for the discovery of rare but ecologically and evolutionarily important eukaryotes.

Biochar–microbe interaction: more protist research is needed

Biochar applications have an enormous impact on the soil microbial community and functionality. However, the majority of the knowledge on biochar–microbe interaction derives almost exclusively from bacterial and fungal studies, while the vast majority of eukaryotic diversity, protists, are mostly neglected. Protists play important roles in the soil ecosystem as microbial predators, decomposers, photoautotrophs, pathogens, and parasites and they are essential for a healthy soil ecosystem. Toward a comprehensive understanding of the effects of biochar application, we need more studies on protists across the full breadth of eukaryotic diversity. The aim of this article is to highlight the research needs and discuss potential research ideas on biochar–protist interaction, which would advance our knowledge of biochar–microbe interaction.HighlightsBiochar–microbe interaction is almost exclusively studied for bacteria and fungi.Only a few studies are available on how soil protists react to biochar application.More research on biochar–protist is needed for a better understanding of biochar–microbe interaction.

Biological control of soft rot in potato by κ-carrageenan carriers encapsulated microbial predators.

The Pectobacterium and Dickeya pectinolytic bacteria are phytopathogens responsible for several macerating diseases on a wide range of crops and ornamental plants. Recently, bacterial predators belonging to the Bdellovibrio and like organisms (BALOs) were shown to efficiently prey on these rot-causing bacteria and reduce soft rot-induced potato slice maceration. In the current research, our novel approach aimed at developing and studying a κ-carrageenan-based encapsulation system for fast-release of entrapped B. bacteriovorus HD100 in high numbers to prevent bacterial soft-rot infections. κ-carrageenan-dried carriers swelled and dissolved upon immersion in water due to a loss of potassium ions which are the main cross-linking agents. Survival rates of the predators after drying were higher for immobilized bdelloplasts (e.g., predator inside the host) compared to attack phase (host-searching, AP) cells, and with the addition of the osmoprotectant trehalose to the carriers. Released encapsulated predators preyed efficiently on soft rot bacteria, with bdelloplasts performing better as compared to AP cells. However, predation dynamics were influenced by the type of added osmoprotectant. Carrageenan-trehalose carriers encapsulating predators were able to reduce soft-rot disease in situ using a potato slice assay. To our knowledge, this research is the first to explore the potential of encapsulated BALOs against phytopathogens. KEY POINTS: • Dissolution of the carriers was affected by potassium concentration in the system. • Encapsulation of bdelloplasts with trehalose best maintained the predator viability. • The encapsulated predators efficiently controlled soft rot in vitro and in situ.

Linear scaling between microbial predator and prey densities in the global ocean.

It has been proposed that microbial predator and prey densities are related through sublinear power laws. We revisited previously published biomass and abundance data and fitted Power-law Biomass Scaling Relationships (PBSRs) between marine microzooplankton predators (Z) and phytoplankton prey (P), and marine viral predators (V) and bacterial prey (B). We analysed them assuming an error structure given by Type II regression models which, in contrast to the conventional Type I regression model, accounts for errors in both the independent and the dependent variables. We found that the data support linear relationships, in contrast to the sublinear relationships reported by previous authors. The scaling exponent yields an expected value of 1 with some spread in different datasets that was well-described with a Gaussian distribution. Our results suggest that the ratios Z/P, and V/B are on average invariant, in contrast to the hypothesis that they systematically decrease with increasing P and B, respectively, as previously thought.