Lysobacter enzymogenes is less-studied, but emerging as a powerful biocontrol bacterium producing multiple antimicrobial weapons including lytic enzymes, toxins, secondary metabolites and protein secretion systems. The loss of surface-attached flagellum, production of heat-stable antifungal factor (HSAF, also named as Ningrongmycin) as a novel antifungal antibiotic, and the use of the type IV secretion system (T4SS) rather than the common type VI secretion system (T6SS) to kill competitor bacteria make this species unique. These distinct features set L. enzymogenes apart from well-studied plant beneficial biocontrol agents, such as Bacillus and Pseudomonas. This review describes what takes L. enzymogenes to be a unique biocontrol warrior by focusing to illustrate how the lack of flagellum governs morphological and functional co-adaptability, what adapted signaling transduction pathways are adopted to coordinate the biosynthesis of HSAF, and how to ecologically adapt plant rhizosphere by cell-to-cell interacting with microbiome members via the bacterial-killing T4SS.

In recent years, an unusual wilt disease affecting Pyrus pyrifolia has been observed in various regions of Jiangsu, China. This disease originates from the roots and progresses with distinctive browning patterns along vascular tissues, even extending over two meters above the ground. These symptoms set it apart from recognized pear diseases and typically lead to the death of affected trees within the same or the following year. Furthermore, this disease exhibits a tendency to spread to neighboring trees even after the removal of affected trees, presenting a substantial threat to pear production. To ascertain the causative agent, the present study encompassed pathogen isolation, morphological and molecular identification, as well as validation experiments adhering to Koch's postulates. The fungal isolates obtained were identified as Fusarium cugenangense based on characteristics of the colonies and conidia, in addition to a phylogenetic analysis using DNA sequences of the translation elongation factor 1-alpha (tef1), calmodulin (CaM), and RNA polymerase second largest subunit (rpb2) genes. Pathogenicity of the isolated F. cugenangense on pear was confirmed by artificial inoculation. By introducing GFP-labeled pathogens into the roots, colonization in stem and leaf tissues was observed via fluorescence microscopy and transmission electron microscopy. Furthermore, these pathogens were successfully reisolated from stems and foliage, conclusively providing evidence of systemic infection within the pear plants. To the best of our knowledge, this is the first report of F. cugenangense causing pear wilt disease in China.

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight in rice, which reduces crop yield and leads to significant economic losses. Bacterial sigma (σ) factors are highly specialized proteins that allow RNA polymerase to recognize and bind to specific promoters. σ⁷⁰ factors also regulate the expression of genes involved in stress response and virulence. However, the role of RpoD in Xoo is still unclear. In this study, we found that σ⁷⁰ factor RpoD is quite conservative among phytopathogenic bacteria, especially in Xanthomonas sp. In Xoo, PXO_RpoD plays an important role in oxidative stress tolerance and cell motility, as well as being essential for full virulence. Cleavage under targets and tagmentation (CUT&Tag) analyses indicated that RpoD mediates the type three secretion system (T3SS) by regulating the regulation of hrpG and hrpX. By performing bacterial one-hybrid and electrophoretic mobility assay (EMSA), we observed that RpoD directly bound to the promoters of hrpG and hrpX. Collectively, these results demonstrate the transcriptional mechanism and pathogenic functions of RpoD in regulating cell motility and oxidative stress response, providing novel insights into potential targets for disease control.