Taxonomy-guided selection of Paraburkholderia busanensis sp. nov.: a versatile biocontrol agent with mycophagy against Colletotrichum scovillei causing pepper anthracnose

Fungal-bacterial interactions leading to increased insect mortality: Trichoderma xixiacum enhances the pathogenicity of Serratia marcescens in Protaetia brevitarsis larvae

Edible insect farming presents significant potential as a sustainable solution to meet the increasing demand for protein and biowaste recycling. However, microbial contamination in rearing substrates poses a serious threat to insect populations. This study investigates the pathogenicity of Serratia marcescens YSMM-S1, isolated from dead Protaetia brevitarsis larvae, and explores its interaction with Trichoderma xixiacum, a fungus co-isolated from the same rearing environment. The identified S. marcescens YSMM-S1 was confirmed as a highly virulent strain, causing 100 % larval mortality within 24 h. In addition, T. xixiacum identified via extensive molecular and morphological characterization, is reported here for the first time in Korea. Co-cultivation and mycophagy assays revealed a significant increase in S. marcescens proliferation in the presence of T. xixiacum, likely through fungal mycelium consumption. Moreover, preinoculation with T. xixiacum in oak-fermented sawdust significantly enhanced S. marcescens population growth and colonization. In vivo assays further demonstrated that co-inoculation of the substrate with both microorganisms resulted in significantly higher larval mortality compared to single inoculations. This study provides novel insights into the complex microbial dynamics in insect-rearing systems, emphasizing the role of T. xixiacum in facilitating bacterial pathogenicity. The findings highlight the need for careful microbial management to prevent outbreaks in mass-rearing environments. This work also contributes to the understanding of fungal-bacterial interactions in insect farming and offers new perspectives on the ecological roles of Trichoderma species in rearing substrates.

The potential of Paraburkholderia species to enhance crop growth

Agrochemicals are the primary alternative for maintaining the high yields necessary to produce sufficient plant-based foods to supply the world population. In recent decades, one of the most extensively explored alternatives to replace agrochemicals and reduce their environmental impact has been the use of microorganism-based products to boost crop yields with less environmental impact. This review focuses on the results of studies that have demonstrated the potential of the genus Paraburkholderia to increase crop yields and be utilized in biofertilizers and biocontrol products. A literature search was performed electronically considering articles and books published until August 19, 2024. We identified 24 species of Paraburkholderia with the ability to improve crop yields after their inoculation by different methods on seeds, seedlings, plantlets, adult crops, or fruits. The effects of these bacteria have been tested under laboratory, greenhouse, or field conditions. These Paraburkholderia species mediate their positive impact on crop growth by direct and indirect plant growth-promoting mechanisms, which include improving nutrient uptake, stimulating growth by phytohormone production, regulation and stimulation of metabolic pathways, induction of abiotic stress tolerance, and disease control by direct pathogen inhibition or induction of systemic resistance in plants. The literature reviewed here supports the use of Paraburkholderia in bio-inputs under the actual panorama of climate change and the necessity to increase sustainable agriculture worldwide.

Paraburkholderia tropica Primes a Multilayered Transcriptional Defense Response to the Nematode Meloidogyne spp. in Tomato

Meloidogyne causes a devastating disease known as root-knot that affects tomatoes and other cash crops worldwide. Conversely, Paraburkholderia tropica has proven beneficial in mitigating the effects of various pathogens in plants. We aimed to unravel the molecular events that underlie the beneficial effects of the bacterium and the detrimental impacts of the nematode when inoculated separately or together in tomato plants. The transcriptional responses induced by P. tropica (TB group (tomato-bacteria group)), Meloidogyne spp. (TN group (tomato-nematode group)) or by the two agents (TBN group (tomato-bacteria-nematode group)) in tomato were assessed by RNA-seq. We implemented a transcript discovery pipeline which allowed the identification of 2283 putative novel transcripts. Differential expression analysis revealed that upregulated transcripts were much more numerous than downregulated ones. At the gene ontology level, the most activated term was 'hydrolase activity acting on ester bonds' in all groups. In addition, when both microbes were inoculated together, 'hydrolase activity acting on O-glycosyl compounds' was activated. This finding suggests defense responses related to lipid and carbohydrate metabolism, membrane remodeling and signal transduction. Notably, defense genes, transcription factors and protein kinases stood out. Differentially expressed transcripts suggest the activation of a multifaceted plant defense response against the nematode occurred, which was exacerbated by pre-inoculation of P. tropica.

Exploring the comparative genome of rice pathogen Burkholderia plantarii: unveiling virulence, fitness traits, and a potential type III secretion system effector

This study presents a comprehensive genomic analysis of Burkholderia plantarii, a rice pathogen that causes blight and grain rot in seedlings. The entire genome of B. plantarii KACC 18964 was sequenced, followed by a comparative genomic analysis with other available genomes to gain insights into its virulence, fitness, and interactions with rice. Multiple secondary metabolite gene clusters were identified. Among these, 12 demonstrated varying similarity levels to known clusters linked to bioactive compounds, whereas eight exhibited no similarity, indicating B. plantarii as a source of potentially novel secondary metabolites. Notably, the genes responsible for tropolone and quorum sensing were conserved across the examined genomes. Additionally, B. plantarii was observed to possess three complete CRISPR systems and a range of secretion systems, exhibiting minor variations among the analyzed genomes. Genomic islands were analyzed across the four genomes, and a detailed study of the B. plantarii KACC 18964 genome revealed 59 unique islands. These islands were thoroughly investigated for their gene contents and potential roles in virulence. Particular attention has been devoted to the Type III secretion system (T3SS), a crucial virulence factor. An in silico analysis of potential T3SS effectors identified a conserved gene, aroA. Further mutational studies, in planta and in vitro analyses validated the association between aroA and virulence in rice. Overall, this study enriches our understanding of the genomic basis of B. plantarii pathogenicity and emphasizes the potential role of aroA in virulence. This understanding may guide the development of effective disease management strategies.