The Role of Serratomolide-like Amino Lipids Produced by Bacteria of Genus Serratia in Nematicidal Activity

The effect of biopolymer stabilisation on biostimulated or bioaugmented mine residue for potential technosol production

Mine waste can be transformed into technosol as an ecological strategy. Despite its importance to soil functions, biological activity is often overlooked. Biopolymers can serve as innovative tools for bioremediation, facilitating chemical reactions and creating networks to encapsulate contaminants. This work aims to assess the use of bioleached and stabilised residues from a tungsten mine for technosol production. The first objective was to evaluate mine tailings for their bioleaching potential by biostimulation or bioaugmentation with strain Diaphorobacter polyhydroxybutyrativorans B2A2W2. The second was to evaluate the effect of Portland cement or biopolymers such as Carboxymethyl Cellulose (CMC) or Xanthan Gum (XG) on the stabilisation of bioleached residues. The impact of biopolymers on residues' characteristics, such as metal leaching, number of cultivable microorganisms, compression strength and ecotoxicity was evaluated using flow systems. Over time, bioleached metallic elements decreased, except for iron (Fe). Biostimulated and stabilised residues exhibited similar trends; both CMC and cement showed low leaching rates and viable microorganisms in the same order (106 CFU × ml-1). However, bioaugmented residue stabilised with XG showed 106 CFU × ml-1 viable microorganisms and increased 2.2-fold Fe leaching than BA_Control. CMC addition to bioaugmented residue reduced 5.9-fold Fe leaching and increased 100-fold viable microorganisms. By utilising both biological and engineering approaches to characterise the technosol, this study contributes to advancing knowledge of technosol production. The residues biostimulated and stabilised with CMC produced a material useful for bio-applications, with low toxicity and metal leaching, useful for bio-applications. XG was the best stabiliser for geotechnical engineering applications, with improved compression strength. In conclusion, the study demonstrates the usefulness of biopolymer treatment for residues and emphasises the importance of selecting the appropriate biopolymer for the intended function of technosols.

Antibacterial peptides from Monochamus alternatus induced oxidative stress and reproductive defects in pine wood nematode through the ERK/MAPK signaling pathway

Pine wilt disease is a devastating disease of pine caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus. Long-term use of chemical nematicides leads to the development of resistance in nematodes and harms the environment. Evaluations for green environmental protection agents, identified the antibacterial peptide, MaltDef1, from Monochamus alternatus which had nematicidal effect. We studied its nematicidal activity and action against PWN. In this study, the antibacterial peptide S-defensin was synthesized from M. alternatus. The results showed that S-defensin caused mortality to the PWN, causing shrinkage, pore, cell membrane dissolution and muscle atrophy. In addition, PWN reproduction was also affected by S-defensin; it decreased in a concentration dependent manner with increasing treatment concentration. By contrast, reactive oxygen species (ROS) in vivo increased in a concentration-dependent manner. We applied transcriptome to analyze the changes in gene expressions in S-defensin treated PWN, and found that the most significantly enriched pathway was the ERK/MAPK signaling pathway. RNAi was used to validate the functions of four differential genes (Let-23, Let-60, Mek-2 and Lin-1) in this pathway. The results showed that knockdown of these genes significantly decreased the survival rate and reproductive yield of, and also increased ROS in PWN. The antibacterial peptide S-defensin had a significant inhibitory effect on the survival and reproduction of PWN, shown by cell membrane damage and intracellular biological oxidative stress via regulating the ERK/MAPK signaling pathway. This indicates that S-defensin has a target in B. xylophilus, against which new green target pesticides can be developed.

Biological Control of Phytopathogens: Mechanisms and Applications

According to the inherent ecological mechanisms within community structures, organismic interactions are mediated by chemical structures and signaling molecules as well as enzymatic activities targeting the vital activities of microbial competitors [...].

The Changes of Microbial Communities and Key Metabolites after Early Bursaphelenchus xylophilus Invasion of Pinus massoniana

Pine wood nematode, Bursaphelenchus xylophilus, is a worldwide pest of pine trees, spreading at an alarming rate and with great ecological adaptability. In the process of causing disease, the nematode causes metabolic disorders and changes in the endophytic microbial community of the pine tree. However, the changes at the pine nidus during early nematode invasion have not been well studied, especially the differential metabolites, in Pinus massoniana, the main host of B. xylophilus in China. In this study, we analyzed the endophytic bacterial and fungal communities associated with healthy and B. xylophilus-caused wilted pine trees. The results show that 1333 bacterial OTUs and 502 fungal OTUs were annotated from P. massoniana stem samples. The abundance of bacterial communities in pine trees varies more following infection by B. xylophilus, but the abundance changes of fungal communities are less visible. There were significant differences in endophytic microbial diversity between wilted and healthy P. massoniana. In wilted pine trees, Actinobacteria and Bacteroidia were differential indicators of bacterial communities, whereas, in healthy pine trees, Rhizobiales in the Proteobacteria phylum were the major markers of bacterial communities. Meanwhile, the differential markers of fungal communities in healthy pines are Malasseziales, Tremellales, Sordariales, and Fusarium, whereas Pleosporaceae is the key marker of fungal communities in wilted pines. Our study examines the effect of changes in the endophytic microbial community on the health of pine trees that may be caused by B. xylophilus infection. In parallel, a non-targeted metabolomic study based on liquid mass spectrometry (LC-MS) technology was conducted on pine trees inoculated with pine nematodes and healthy pine trees with a view to identifying key compounds affecting early pine lesions. Ultimately, 307 distinctly different metabolites were identified. Among them, the riboflavin metabolic pathway in pine trees may play a key role in the early pathogenesis of pine wood nematode disease.