The soil-dwelling, opportunistic pathogenic bacterium "Bacillus nematocida" B16 exhibits strong killing activities against a variety of pathogenic nematodes via a “Trojan horse” mechanism that can kill worm species like Caenorhabditis elegans. The bacterial strain CPCC 101271 was previously isolated from the intestines of C. elegans that were recovered from natural habitats and can serve as a probiotic for C. elegans, while also assisting in resistance to infection by the pathogenic strain B16. In this study, the lifespan of C. elegans fed with strain CPCC 101271 cells was extended by approximately 40% compared with that of worms fed with Escherichia coli OP50 cells. In addition, the colonization of C. elegans by the pathogenic bacterium "B. nematocida" B16 was inhibited when pre-fed with strain CPCC 101271. Metagenomic sequence analysis of intestinal microbiota of C. elegans fed with strain CPCC 101271 and infected with B16 revealed that pre-feeding worms with CPCC 101271 improved the diversity of the intestinal bacteria. Moreover, community structure significantly varied in coordination with Stenotrophomonas spp. and Bacillus spp. abundances when competition between strains CPCC 101271 and B16 was evaluated. In conclusion, the nematode microbiota strain CPCC 101271 assisted in its host resistance to colonization by the pathogen "Bacillus nematocida" and can also promote life span-prolongation in C. elegans. These results underscore that understanding the interactions between C. elegans microbiota and pathogens can provide new insights into achieving effective biological control of agricultural pests.

Symbiotic microorganisms in the intestinal tract can influence the general fitness of their hosts and contribute to protecting them against invading pathogens. In this study, we obtained isolate Phytobacter diazotrophicus SCO41 from the gut of free-living nematode Caenorhabditis elegans that displayed strong colonization-resistance against invading biocontrol bacterium Bacillus nematocida B16. The colonization-resistance phenotype was found to be mediated by a 37-kDa extracellular protein that was identified as flagellin (FliC). With the help of genome information, the fliC gene was cloned and heterologously expressed in E. coli. It could be shown that the B. nematocida B16 grows in chains rather than in planktonic form in the presence of FliC. Scanning Electronic Microscopy results showed that protein FliC-treated B16 bacterial cells are thinner and longer than normal cells. Localization experiments confirmed that the protein FliC is localized in both the cytoplasm and the cell membrane of B16 strain, in the latter especially at the position of cell division. ZDOCK analysis showed that FliC could bind with serine/threonine protein kinase, membrane protein insertase YidC and redox membrane protein CydB. It was inferred that FliC interferes with cell division of B. nematocidal B16, therefore inhibiting its colonization of C. elegans intestines in vivo. The isolation of P. diazotrophicus as part of the gut microbiome of C. elegans not only provides interesting insights about the lifestyle of this nitrogen-fixing bacterium, but also reveals how the composition of the natural gut microbiota of nematodes can affect biological control efforts by protecting the host from its natural enemies.

Polyethylene terephthalate (PET) microplastic pollution poses significant threats to organisms and ecological health, and microbial degradation has emerged as a promising bioremediation strategy. This study isolated 85 bacterial strains from plastic-contaminated sludge and wastewater, and screened them for growth on PET granules as the sole carbon source. Three positive strains W106, W107, and SG211 were obtained; W107, identified as Acinetobacter sp. based on phenotypic and biochemical characteristics, showed the highest degradation efficiency. FTIR and HPLC confirmed the depolymerization of PET with the detection of terephthalic acid (TPA), while SEM verified the physical erosion of PET granules. The esterase gene estZ with 100% amino acid identity to Acinetobacter soli strain M3-1-68 EstB was cloned from Acinetobacter sp.W107 and recombinantly expressed in Escherichia coli BL21 (pET-28a). The recombinant strain (Rm-W107) enhanced PET degradation, with 6.87-fold higher TPA release over 5 days than cell-free controls, verifying EstZ's role in PET hydrolysis. Recombinant Estz (Rm-EstZ) had optimal activity at 40°C and pH 6.5, activated by 1 mM Fe³ ⁺ and 5 mM Fe²⁺ but inhibited by Zn²⁺ and Ca²⁺. Kinetic analysis showed moderate p-NPA substrate affinity (K_m = 4.917 ± 1.001 mM). These findings expand the repertoire of PET-degrading microorganisms, provide new insights into enzymatic bioremediation mechanisms, and highlight the whole-cell biocatalyst's potential for industrial plastic waste management.

The soil-dwelling opportunistic bacterium Bacillus nematocida B16 shows comparatively strong killing activities against a variety of pathogenic nematodes. A bacterial strain CPCC 101271^T, isolated from intestines of C. elegans in natural habitats, was found not only to be probiotics for C. elegans but also assist in resisting pathogen B16 infection. The lifespan of Caenorhabditis elegans fed on strain CPCC 101271^T was extended by approximately 40% compared with that of worms fed on Escherichia coli OP50. In addition, the colonization of C. elegans by the pathogenic bacterium B. nematocida B16 was inhibited when it was pre-fed with strain CPCC 101271^T. Based on a polyphasic taxonomy study including genotypic, chemotaxonomic and phenotypic characteristics, we propose that strain CPCC 101271^T represents a novel bacterial species with the name Stenotrophomonas nematodicola sp. nov. and CPCC 101271^T as the type strain. Metagenomic sequence analysis of the intestinal microbiota of C. elegans fed with strain CPCC 101271^T and then infected with B16 revealed that pre-feeding with CPCC 101271^T improved the diversity of intestinal bacteria, while the community structure varied significantly together with the fluctuation of Stenotrophomonas spp. and Bacillus spp. abundance during competition between strain CPCC 101271^T and B16. In conclusion, the nematode microbiota strain CPCC 101271^T, a novel species of the genus Stenotrophomonas, assisted in its host resistance to the pathogen Bacillus nematocida colonization, so as to act as an intestinal life span-prolonging for C. elegans.