Two Functional Fatty Acyl Coenzyme A Ligases Affect Free Fatty Acid Metabolism To Block Biosynthesis of an Antifungal Antibiotic in Lysobacter enzymogenes

Unveiling the Role of Diffusible Signal Factor-Family Quorum Sensing Signals in Regulating Behavior of Xanthomonas and Lysobacter

Diffusible signal factor (DSF) family signals represent a unique group of quorum sensing (QS) chemicals that modulate a wide range of behaviors for bacteria to adapt to different environments. However, whether DSF-mediated QS signaling acts as a public language to regulate the behavior of biocontrol and pathogenic bacteria remains unknown. In this study, we present groundbreaking evidence demonstrating that RpfFXc1 or RpfFOH11 could be a conserved DSF-family signal synthase in Xanthomonas campestris or Lysobacter enzymogenes. Interestingly, we found that both RpfFOH11 and RpfFXc1 have the ability to synthesize DSF and BDSF signaling molecules. DSF and BDSF positively regulate the biosynthesis of an antifungal factor (heat-stable antifungal factor, HSAF) in L. enzymogenes. Finally, we show that RpfFXc1 and RpfFOH11 have similar functions in regulating HSAF production in L. enzymogenes, as well as the virulence, synthesis of virulence factors, biofilm formation, and extracellular polysaccharide production in X. campestris. These findings reveal a previously uncharacterized mechanism of DSF-mediated regulation in both biocontrol and pathogenic bacteria.

Regulatory Effects of Diverse DSF Family Quorum-Sensing Signals in Plant-Associated Bacteria

Numerous bacterial species employ diffusible signal factor (DSF)-based quorum sensing (QS) as a widely conserved cell-cell signaling communication system to collectively regulate various behaviors crucial for responding to environmental changes. cis-11-Methyl-dodecenoic acid, known as DSF, was first identified as a signaling molecule in Xanthomonas campestris pv. campestris. Subsequently, many structurally related molecules have been identified in different bacterial species. This review aims to provide an overview of current understanding regarding the biosynthesis and regulatory role of DSF signals in both pathogenic bacteria and a biocontrol bacterium. Recent studies have revealed that the DSF-based QS system regulates antimicrobial factor production in a cyclic dimeric GMP-independent manner in the biocontrol bacterium Lysobacter enzymogenes. Additionally, the DSF family signals have been found to be involved in suppressing plant innate immunity. The discovery of these diverse signaling mechanisms holds significant promise for developing novel strategies to combat stubborn plant pathogens. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Antifungal Compound from the Predatory Bacterium Lysobacter enzymogenes Inhibits a Plant Pathogenic Fungus by Targeting the AAA ATPase VpVeb1

Heat-stable antifungal factor (HSAF) isolated from Lysobacter enzymogenes is considered a potential biocontrol agent. However, the target of HSAF in phytopathogenic fungi remains unclear. In this study, we investigated the target of HSAF in Valsa pyri that causes fatal pear Valsa canker. Thirty-one HSAF-binding proteins were captured and identified by surface plasmon resonance (SPR) and high-performance liquid chromatography-mass spectrometry (LC-MS/MS), and 11 deletion mutants were obtained. Among these mutants, only ΔVpVEB1 showed decreased sensitivity to HSAF. Additionally, ΔVpVEB1 exhibited significantly reduced virulence in V. pyri. Molecular docking and SPR results revealed that HSAF bound to threonine 569 and glycine 570 of VpVeb1, which are crucial for AAA ATPase activity. Another study showed that HSAF could decrease the ATPase activity of VpVeb1, leading to the reduced virulence of V. pyri. Taken together, this study first identified the potential target of HSAF in fungi. These findings will help us better understand the model of action of HSAF to fungi.

Dynamics associated with fermentation and aerobic deterioration of high-moisture Italian ryegrass silage made using Lactobacillus plantarum and caproic acid

AIMS

To determine the fermentation quality, aerobic stability, and chemical composition of Italian ryegrass silage prepared with Lactobacillus plantarum (LP), caproic acid (CA), and their combination during ensiling and feed-out phase.

METHODS AND RESULTS

Six treatments: control (CON), LP, 0.15% caproic acid (LCA), 0.2% caproic acid (HCA), LCA + LP, and HCA + LP were employed for 30 days ensiling and an 8-days aerobic stability test. LP had similar pH value and lactic acid content with LCA + LP, while the contents of NH3-N and total VFAs in LCA + LP were significantly lower than those in LP and CON, and the fermentation quality of LCA + LP performed best among all silages. As air-exposure extended, contents of water-soluble carbohydrates (WSC), lactic, and acetic acids decreased, while pH, and NH3-N content increased significantly. The population of lactic acid bacteria gradually decreased in contrast to increased counts of aerobic bacteria and yeasts. Compared with LCA, 0.2% CA delayed the aerobic deterioration as judged by a slower increase in pH and high residual of WSC and lactic acid, and negligible ethanol content and anaerobe spores counts remained in HCA at the end of air exposure. Compared with CON (73 h), LP showed less aerobic stability (38 h), whereas HCA and HCA + LP prolonged aerobic stability for 210 and 152 h, better than LCA (109 h) and LCA + LP (146 h).

CONCLUSIONS

Lactobacillus plantarum apparently improved the fermentation quality, and combined with CA exhibited greater efficiency in inhibiting undesirable microorganism during ensiling. CA at 0.2% optimally extended the aerobic stability.

Description of Fervidibacillus gen. nov. with Two Species, Fervidibacillus albus sp. nov., and Fervidibacillus halotolerans sp. nov., Isolated from Tidal Flat Sediments and Emendation of Misclassificed Taxa in the Genus Caldibacillus

Two Gram-stain-positive, motile, endospore-forming, facultatively anaerobic strains, designated MEBiC13591^T and MEBiC13594^T, were isolated from tidal flat sediment of the Incheon City on the west coast of Korea. Growth of both novel strains was observed at pH 5-9 (optimum, pH 7-7.5), and in 0-8% NaCl (optimum, 2% for MEBiC13591^T and 3% for MEBiC13594^T). Strains MEBiC13591^T and MEBiC13594^T grew optimally at 50 °C, (37.5-56.1 °C) and 44 °C (20.7-50.7 °C), respectively. The main cellular fatty acids of strain MEBiC13591^T were iso-C_15: 0, anteiso-C_15: 0, iso-C_16: 0, iso-C_17: 0 and anteiso-C_17: 0, while those for strain MEBiC13594^T were C_14: 0, iso-C_14: 0, iso-C_15: 0, anteiso-C_15: 0 and C_16: 0. In both taxa, the major isoprenoid was MK-7. The genomic DNA G + C contents were 34.1 and 37.0 mol% for MEBiC13591^T and MEBiC13594^T, respectively. A 16S rRNA gene sequence analysis revealed that the novel strains showed high similarity with members of the genera Aeribacillus (95.0%) and Caldibacillus (93.5-94.5%); however, showed lower than 90% with Caldibacillus debilis Tf^T. Phylogenetic and Phylogenomic analysis revealed that two novel strains comprised distinct phyletic line with members formerly assigned to Caldibacillus. Based on genomic indices, such as AAI and ANI, members formerly affiliated with Caldibacillus and Bacillus as well as the novel strains should be classified into five independent genera. Based on the phenotypic, genomic and biochemical data, strains MEBiC13591^T and MEBiC13594^T represent two novel species in the novel genus, for which the names Fervidibacillus albus gen. nov., sp. nov. (MEBiC13591^T [= KCCM 43317^T = KCTC 43181^T = JCM 33662^T = MCCC 1K04565^T]), and Fervidibacillus halotolerans sp. nov. (MEBiC13594^T [= KCTC 43182^T = JCM 34001^T]) are proposed. Three additional genera Caldifermentibacillus, Palidibacillus, and Perspicuibacillus are also proposed by reclassification of the several species with valid names that formerly affiliated with the genera Caldibacillus.

Spatial transcriptomes and microbiota reveal immune mechanism that respond to pathogen infection in the posterior intestine of Sebastes schlegelii

The intestine is a site of immune cell priming at birth. Therefore, spatial transcriptomes were performed to define how the transcriptomic landscape was spatially organized in the posterior intestine of Sebastes schlegelii following Edwardsiella piscicida infection. In the healthy condition, we identified a previously unappreciated molecular regionalization of the posterior intestine. Following bacterial infection, most immune-related genes were identified in mucosa layer. Moreover, investigation of immune-related genes and genes in immune-related KEGG pathways based on spatial transcriptomes shed light on which sections of these genes are in the posterior intestine. Meanwhile, the high expression of genes related to regeneration also indicated that the posterior intestine was responding to the invasion of pathogens by constantly proliferating new cells. In addition, the increasing microbiota communities indicated that these bacteria maintained posterior intestine integrity and shaped the mucosal immune system. Taken together, spatial transcriptomes and microbiota compositions have significant implications for understanding the immune mechanism that responds to E. piscicida infection in the posterior intestine of S. schlegelii, which also provides a theoretical basis for the spatial distribution of immune genes and changes in bacterial flora in other teleosts in the process of resisting pathogens.

The Xanthomonas citri Reverse Fitness Deficiency by Activating a Novel β-Glucosidase Under Low Osmostress

Bacteria can withstand various types of environmental osmostress. A sudden rise in osmostress affects bacterial cell growth that is countered by activating special genes. The change of osmostress is generally a slow process under the natural environment. However, the collective response of bacteria to low osmostress remains unknown. This study revealed that the deletion of phoP (ΔphoP) from X. citri significantly compromised the growth and virulence as compared to the wild-type strain. Interestingly, low osmostress reversed physiological deficiencies of X. citri phoP mutant related to bacterial growth and virulence. The results also provided biochemical and genetic evidence that the physiological deficiency of phoP mutant can be reversed by low osmostress induced β-glucosidase (BglS) expression. Based on the data, this study proposes a novel regulatory mechanism of a novel β-glucosidase activation in X. citri through low osmostress to reverse the fitness deficiency.

The predatory soil bacterium Lysobacter reprograms quorum sensing system to regulate antifungal antibiotic production in a cyclic-di-GMP-independent manner

Soil bacteria often harbour various toxins to against eukaryotic or prokaryotic. Diffusible signal factors (DSFs) represent a unique group of quorum sensing (QS) chemicals that modulate interspecies competition in bacteria that do not produce antibiotic-like molecules. However, the molecular mechanism by which DSF-mediated QS systems regulate antibiotic production for interspecies competition remains largely unknown in soil biocontrol bacteria. In this study, we find that the necessary QS system component protein RpfG from Lysobacter, in addition to being a cyclic dimeric GMP (c-di-GMP) phosphodiesterase (PDE), regulates the biosynthesis of an antifungal factor (heat-stable antifungal factor, HSAF), which does not appear to depend on the enzymatic activity. Interestingly, we show that RpfG interacts with three hybrid two-component system (HyTCS) proteins, HtsH1, HtsH2, and HtsH3, to regulate HSAF production in Lysobacter. In vitro studies show that each of these proteins interacted with RpfG, which reduced the PDE activity of RpfG. Finally, we show that the cytoplasmic proportions of these proteins depended on their phosphorylation activity and binding to the promoter controlling the genes implicated in HSAF synthesis. These findings reveal a previously uncharacterized mechanism of DSF signalling in antibiotic production in soil bacteria.

Li et al shows that the quorum sensing system component protein RpfG from Lysobacter, in addition to being a cyclic dimeric GMP (c-di-GMP) phosphodiesterase, also regulates the biosynthesis of an antifungal factor. They show that RpfG regulates the production of HSAF through a direct interaction with three hybrid two component system (HyTCS) proteins, providing insights into the antifungal defence in soil bacteria.

Separation of Heat-Stable Antifungal Factor From Lysobacter enzymogenes Fermentation Broth via Photodegradation and Macroporous Resin Adsorption

Heat-stable antifungal factor (HSAF) is produced by the fermentation of Lysobacter enzymogenes, which is known for its broad-spectrum antifungal activity and novel mode of action. However, studies on the separation of HSAF have rarely been reported. Herein, alteramide B (the main byproduct) was removed firstly from the fermentation broth by photodegradation to improve the purity of HSAF. Then, the separation of HSAF via adsorption by macroporous adsorption resins (MARs) was evaluated and NKA resin showed highest static adsorption and desorption performances. After optimizing the static and dynamic adsorption characteristics, the content of HSAF in the purified product increased from 8.67 ± 0.32% (ethyl acetate extraction) to 31.07 ± 1.12% by 3.58-fold. These results suggest that the developed strategy via photodegradation and macroporous resin adsorption is an effective process for the separation of HSAF, and it is also a promising method for the large-scale preparation of HSAF for agricultural applications.

Lysobacter penaei sp. nov., isolated from intestinal content of a Pacific white shrimp (Penaeus vannamei)

The polyphasic taxonomic approach was used to characterize a novel bacteria strain, designated SG-8^T, which was isolated from intestinal content of a Pacific white shrimp (Penaeus vannamei). Cells were Gram-stain-negative, aerobic, non-gliding rods. Growth occurred at 10-45 °C (optimum, 20-30 °C), pH 5.0-10.0 (optimum, 6.0-7.0) and in 0-6.0 % (w/v) NaCl (optimum, 0-4.0 %). The 16S rRNA gene sequence of strain SG-8^T showed the highest sequence similarity to Lysobacter maris KMU-14^T (98.6 %). On phylogenetic trees, strain SG-8^T formed a stable cluster with Lysobacter maris KMU-14^T, Lysobacter alkalisoli SJ-36^T, Lysobacter spongiae 119BY6-57^T and Lysobacter aestuarii S2-C^T. The average nucleotide identity and digital DNA-DNA hybridization values between strain SG-8^T and the four reference type strains listed above were 83.3, 82.3, 83.5, 83.3% and 22.8, 22.7, 22.7, 22.9 %, respectively. The major fatty acids (>5 %) were iso-C_15 : 0, summed feature 9 (iso-C_17 : 1  ω9c and/or 10-methyl C_16 : 0), iso-C_16 : 0, summed feature 3 (C_16 : 1  ω6c and/or C_16 : 1  ω7c), iso-C_17 : 0, iso-C_11 : 0 3OH and iso-C_11 : 0. Ubiquinone-8 (Q-8) was the only respiratory quinone. The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol. The DNA G+C content was 68.8 mol%. Based on the results of genomic, phylogenetic, phenotypic and chemotaxonomic analyses, strain SG-8^T represents a novel species of the genus Lysobacter, for which the name Lysobacter penaei sp. nov. is proposed. The type strain is SG-8^T (=GDMCC 1.1817^T=KACC 21942^T).