Crab shell meal promotes root-knot nematode control through shifts in soil microbial communities and enhanced nitrification.

With growing environmental awareness, eco-friendly agricultural practices are gaining increased attention. Among these, crab shell meal (CSM) is recognized for its potential to suppress root-knot nematodes (Meloidogyne spp.), largely through the enrichment of chitinolytic bacteria, particularly members of the phylum Actinobacteriota. However, the broader effects of CSM on the soil microbiome remain poorly understood. This study employed 16S amplicon metagenomics to investigate the impact of CSM application on the soil bacterial community associated with root-knot nematode-infected cucumber (Cucumis sativus L.) in a pot experiment. Plant growth parameters and soil chemical properties were also assessed. CSM application at concentrations ranging from 0% to 4% significantly altered the soil microbiome, increasing in the relative abundances of Firmicutes and Actinobacteriota in a dose-dependent manner. These microbial shifts were associated with enhanced cucumber growth and reduced nematode infection severity. Functional predictions indicated that CSM-enriched microbial communities exhibited higher potential for chitin hydrolysis and nitrification, processes that likely contributed to nematode suppression and plant growth promotion. By contrast, the introduction of Streptomyces as a biocontrol agent was less effective, as this strain struggled to establish within the potting system. Overall, the application of CSM successfully enhanced the abundance of chitinolytic bacteria and soil nitrification, providing a dual benefit of nematode control and improved plant growth.