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Summary A vast array of herbivorous arthropods live with symbiotic microorganisms. However, little is known about the nature and functional mechanism of bacterial effects on plant defense responses towards herbivores. We explored the role of microbes present in extracts of oral secretion (OS) isolated from larvae of Spodoptera litura, a generalist herbivore, in phytohormone signaling‐dependent defense responses in Arabidopsis thaliana (Arabidopsis). In response to mechanical damage (MD) with application of bacteria‐free OS (OS–) prepared by sterilization or filtration of OS, Arabidopsis leaves exhibited enhanced de novo synthesis of oxylipins, and induction of transcript abundance of the responsible genes, in comparison to those in leaves with MD + nonsterilized OS (OS+), indicating that OS bacteria serve as suppressors of these genes. By contrast, de novo synthesis/signaling of salicylic acid and signaling of abscisic acid were enhanced by OS bacteria. These signaling networks were cross‐regulated by each other. Meta‐analysis of OS bacteria identified 70 bacterial strains. Among them was Staphylococcus epidermidis, an anaerobic staphylococcus that was shown to contribute to the suppression/manipulation of phytohormone‐dependent plant defense signaling. The presence of OS bacteria was consequently beneficial for S. litura larvae hosted by Brassicaceae.

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Large amounts of plant biomass are produced by public work projects. This plant biomass was evaluated as an aid for the dewatering of sludge from a sewage treatment plant. The relationships were investigated between the different structural types of plant biomass (grass clippings, pruned branches of Japanese black pine, and bamboo powder) and their dewaterability potential in digested sludge. Microscopic observations revealed that grass fibrous materials and Japanese black pine needles had hollow structures. However, xylem, bark parts of Japanese black pine, and bamboo culms exhibited woody cell structures. The difference in water retention value of grass clippings after filtration and centrifugation was higher than that of Japanese pine and bamboo, indicating that the water present within the pores of grass fibrous materials could be easily removed. Plant biomass was captured inside the floc when digested sludge was mixed with plant biomass and flocculation was performed by adding a flocculant. The addition of grass clippings exhibited better dewaterability compared with both Japanese black pine and bamboo. The grass fibrous materials used as a dewatering aid effectively improved the dewaterability of the digested sludge because the water in a sludge floc may be drained from within the grass fibrous materials.