Garcia-Rodriguez, N. M. | Search bioRxiv

bioRxiv2025

Bacillus subtilis strain UD1022 as a biocontrol agent against Magnaporthe oryzae, the rice blast pathogen

Rice blast disease, caused by Magnaporthe oryzae, is a major threat to global rice production, necessitating sustainable disease management strategies. Compared to chemical pesticides, biocontrol agents, such as beneficial microbe antagonists, offer a sustainable approach to naturally inhibit plant pathogens. This study evaluates the biocontrol potential of Bacillus subtilis UD1022 against M. oryzae through both direct antagonism and volatile-mediated inhibition. In dual culture assays, UD1022 significantly inhibited fungal growth. Furthermore, a stacking plate assay demonstrated that UD1022 produces volatile organic compounds (VOCs) that suppress fungal growth. Beyond vegetative growth inhibition, UD1022 also disrupted key infection processes of M. oryzae. Spore germination was reduced by 50%, while appressorium formation decreased by approximately 44% in UD1022-treated samples. In planta assays revealed that UD1022-treated rice plants exhibited a substantial reduction in disease severity compared to untreated controls. This reduction correlated with the upregulation of key defense genes in the salicylic acid, jasmonic acid, and ethylene signaling pathways, suggesting that UD1022 primes systemic resistance in rice plants. These findings establish UD1022 as a potent biocontrol agent capable of suppressing M. oryzae through direct antagonism, VOC-mediated inhibition, and induction of systemic resistance. This study underscores the potential of UD1022 as an eco-friendly alternative to chemical fungicides for managing rice blast disease. IMPORTANCEMagnaporthe oryzae is a destructive fungal pathogen that causes rice blast disease, leading to significant yield losses and threatening global food security. Here, we investigated the biocontrol potential of Bacillus subtilis UD1022, a beneficial rhizobacterium known for its plant growth-promoting and antifungal properties. Our in vitro and in planta studies revealed that UD1022 suppresses M. oryzae through direct antagonism, volatile organic compound (VOC)-mediated inhibition, and the induction of systemic resistance in rice. These findings demonstrate UD1022 as a promising candidate for microbial-based disease management and the role of beneficial bacteria in enhancing crop protection. This research contributes to the development of sustainable agricultural practices by leveraging naturally occurring microbes to improve plant resilience and disease resistance.

microbiology↗

bioRxiv2022

Enzymatic Specificity of Conserved Rho GTPase Deamidases Promotes Invasion of Vibrio parahaemolyticus at the Expense of Infection

Vibrio parahaemolyticus is among the leading causes of bacterial seafood-borne acute gastroenteritis. Like many intracellular pathogens, V. parahaemolyticus invades host cells during infection by deamidating host small Rho GTPases. The Rho GTPase deamidating activity of VopC, a type three secretion system (T3SS) translocated effector, drives V. parahaemolyticus invasion. The intracellular pathogen uropathogenic Escherichia coli (UPEC) invades host cells by secreting a VopC homolog, the secreted toxin cytotoxic necrotizing factor one (CNF1). Because of the homology between VopC and CNF1, we hypothesized topical application of CNF1 during V. parahaemolyticus infection could supplement VopC activity. Here, we demonstrate that CNF1 improves the efficiency of V. parahaemolyticus invasion, a bottleneck in V. parahaemolyticus infection, across a range of doses. CNF1 increases V. parahaemolyticus invasion independent of both VopC and the T3SS altogether, but leaves a disproportionate fraction of intracellular bacteria unable to escape the endosome and complete their infection cycle. This phenomenon holds true in the presence or absence of VopC, but is particularly pronounced in the absence of a T3SS. The native VopC, by contrast, promotes a far less efficient invasion, but permits the majority of internalized bacteria to escape the endosome and complete their infection cycle. These studies highlight the significance of enzymatic specificity during infection, as virulence factors (VopC and CNF1 in this instance) with similarities in function (bacterial uptake), catalytic activity (deamidation), and substrates (Rho GTPases) are not sufficiently interchangeable for mediating a successful invasion for neighboring bacterial pathogens. IMPORTANCEMany species of intracellular bacterial pathogens target host small Rho-GTPases to initiate invasion, including the human pathogens Vibrio parahaemolyticus and uropathogenic Eschericia coli (UPEC). The type three secretion system (T3SS) effector VopC of V. parahaemolyticus promotes invasion through the deamidation of Rac1 and CDC42 in the host, whereas the secreted toxin cytotoxic necrotizing factor one (CNF1) drives UPECs internalization through the deamidation of Rac1, CDC42, and RhoA. Despite these similarities in the catalytic activity of CNF1 and VopC, we observed the two enzymes were not interchangeable. Although CNF1 increased V. parahaemolyticus endosomal invasion, most intracellular V. parahaemolyticus aborted their infection cycle and remained trapped in endosomes. Our findings illuminate how the precise biochemical fine-tuning of T3SS effectors is essential for efficacious pathogenesis. They moreover pave the way for future investigations into the biochemical mechanisms underpinning V. parahaemolyticus endosomal escape, and more broadly, the regulation of successful pathogenesis.

microbiology↗