Isolation of Klebsiella pneumoniae and Pseudomonas aeruginosa from entomopathogenic nematode-insect host relationship to examine bacterial pathogenicity on Trichoplusia ni.

Klebsiella pneumoniae was isolated from infected pupae of Galleria mellonella and Pseudomonas aeruginosa was isolated from the entomopathogenic nematode Heterorhabditis bacteriophora hosted within the pupae of G. mellonella. Insect consumption and surface application of P. aeruginosa resulted in 83.33% and 81.66% mortality of Trichoplusia ni larvae, respectively. In contrast, 50% mortality was shown when T. ni larvae were fed with K. pneumoniae, and no larvae were killed when applying the bacterium to the larval cuticle. This report shows that two opportunistic human pathogens found in the insect-nematode ecosystem could kill insect pests.

Soil microbiome disruption reveals specific and general plant-bacterial relationships in three agroecosystem soils.

Soil microbiome disruption methods are regularly used to reduce populations of microbial pathogens, often resulting in increased crop growth. However, little is known about the effect of soil microbiome disruption on non-pathogenic members of the soil microbiome. Here, we applied soil microbiome disruption in the form of moist-heat sterilization (autoclaving) to reduce populations of naturally occurring soil microbiota. The disruption was applied to analyze bacterial community rearrangement mediated by four crops (corn, beet, lettuce, and tomato) grown in three historically distinct agroecosystem soils (conventional, organic, and diseased). Applying the soil disruption enhanced plant influence on rhizosphere bacterial colonization, and significantly different bacterial communities were detected between the tested crops. Furthermore, bacterial genera showed significant abundance increases in ways both unique-to and shared-by each tested crop. As an example, corn uniquely promoted abundances of Pseudomonas and Sporocytophaga, regardless of the disrupted soil in which it was grown. Whereas the promotion of Bosea, Dyadobacter and Luteoliobacter was shared by all four crops when grown in disrupted soils. In summary, soil disruption followed by crop introduction amplified the plant colonization of potential beneficial bacterial genera in the rhizosphere.

Methods for Root Exudate Collection and Analysis.

Plant root exudation has long been recognized as a vital communication system between plants and microbial communities populating the rhizosphere. Due to the high complexity of the collection process and analysis, a variety of techniques have been developed to mimic natural exudation conditions. In addition, significant progress improving existing techniques and developing new methodologies of root exudate collection and analysis have been made. However, optimal standard methods that compare closely with environmental soil conditions are not yet available. In this review, we provide an overview of all those topics and provide suggestions for improvement.

A novel approach to determine generalist nematophagous microbes reveals Mortierella globalpina as a new biocontrol agent against Meloidogyne spp. nematodes.

Root-knot nematodes (RKN) such as Meloidogyne spp. are among the most detrimental pests in agriculture affecting several crops. New methodologies to manage RKN are needed such as efficient discovery of nematophagous microbes. In this study, we developed an in vitro high-throughput method relying on the free-living nematode Caenorhabditis elegans and the infection of those nematodes with a soil slurry containing a microbiome likely to house nematophagous microbes. Nematodes were monitored for presence of infection and sub-cultured repeatedly for the purpose of isolating pure cultures of the microbe responsible for conferring the nematicidal activity. Once soil microbes were confirmed to be antagonistic to C. elegans, they were tested for pathogenicity against Meloidogyne chitwoodi. Using this methodology, the fungal isolate Mortierella globalpina was confirmed to be pathogenic in vitro against M. chitwoodi by nematode trapping via hyphal adhesion to the cuticle layer, penetration of the cuticle layer, and subsequently digestion of its cellular contents. M. globalpina was also observed to reduce disease symptomology of RKNs in vivo via significant reduction of root-galls on tomato (Solanum lycopersicum var. Rutgers).