The Lysobacter capsici AZ78 Genome Has a Gene Pool Enabling it to Interact Successfully with Phytopathogenic Microorganisms and Environmental Factors

Genetic Basis and Expression Pattern Indicate the Biocontrol Potential and Soil Adaption of Lysobacter capsici CK09

Lysobacter species have attracted increasing attention in recent years due to their capacities to produce diverse secondary metabolites against phytopathogens. In this research, we analyzed the genomic and transcriptomic patterns of Lysobacter capsici CK09. Our data showed that L. capsici CK09 harbored various contact-independent biocontrol traits, such as fungal cell wall lytic enzymes and HSAF/WAP-8294A2 biosynthesis, as well as several contact-dependent machineries, including type 2/4/6 secretion systems. Additionally, a variety of hydrolytic enzymes, particularly extracellular enzymes, were found in the L. capsici CK09 genome and predicted to improve its adaption in soil. Furthermore, several systems, including type 4 pili, type 3 secretion system and polysaccharide biosynthesis, can provide a selective advantage to L. capsici CK09, enabling the species to live on the surface in soil. The expression of these genes was then confirmed via transcriptomic analysis, indicating the activities of these genes. Collectively, our research provides a comprehensive understanding of the biocontrol potential and soil adaption of L. capsici CK09 and implies the potential of this strain for application in the future.

Widely targeted metabolomic, transcriptomic, and metagenomic profiling reveal microbe-plant-metabolic reprogramming patterns mediated by Streptomyces pactum Act12 enhance the fruit quality of Capsicum annuum L

Plant growth-promoting rhizobacteria, such as Streptomyces pactum Act12, promote crop growth and stress resistance, but their contribution to fruit quality is still poorly understood. Herein we conducted a field experiment to ascertain the effects of S. pactum Act12-mediated metabolic reprogramming and underlying mechanisms in pepper (Capsicum annuum L.) fruit based on widely targeted metabolomic and transcriptomic profiling. We additionally performed metagenomic analysis to elucidate the potential relationship between S. pactum Act12-mediated reshaping of rhizosphere microbial communities and pepper fruit quality. Soil inoculation with S. pactum Act12 considerably increased the accumulation of capsaicinoids, carbohydrates, organic acids, flavonoids, anthraquinones, unsaturated fatty acids, vitamins, and phenolic acids in pepper fruit samples. Consequently, fruit flavor, taste, and color were modified, accompanied by elevated contents of nutrients and bioactive compounds. Increased microbial diversity and recruitment of potentially beneficial taxa were observed in inoculated soil samples, with crosstalk between microbial gene functions and pepper fruit metabolism. The reformed structure and function of rhizosphere microbial communities were closely associated with pepper fruit quality. Our findings indicate that S. pactum Act12-mediated interactions between rhizosphere microbial communities and pepper plants are responsible for intricate fruit metabolic reprogramming patterns, which enhance not only overall fruit quality but also consumer acceptability.

Exopolysaccharide-producing bacteria enhanced Pb immobilization and influenced the microbiome composition in rhizosphere soil of pakchoi (Brassica chinensis L.)

Lead (Pb) contamination of planting soils is increasingly serious, leading to harmful effects on soil microflora and food safety. Exopolysaccharides (EPSs) are carbohydrate polymers produced and secreted by microorganisms, which are efficient biosorbent materials and has been widely used in wastewater treatment to remove heavy metals. However, the effects and underlying mechanism of EPS-producing marine bacteria on soil metal immobilization, plant growth and health remain unclear. The potential of Pseudoalteromonas agarivorans Hao 2018, a high EPS-producing marine bacterium, to produce EPS in soil filtrate, immobilize Pb, and inhibit its uptake by pakchoi (Brassica chinensis L.) was studied in this work. The effects of strain Hao 2018 on the biomass, quality, and rhizospheric soil bacterial community of pakchoi in Pb-contaminated soil were further investigated. The results showed that Hao 2018 reduced the Pb concentration in soil filtrate (16%–75%), and its EPS production increased in the presence of Pb2+. When compared to the control, Hao 2018 remarkably enhanced pakchoi biomass (10.3%–14.3%), decreased Pb content in edible tissues (14.5%–39.2%) and roots (41.3%–41.9%), and reduced the available Pb content (34.8%–38.1%) in the Pb-contaminated soil. Inoculation with Hao 2018 raised the pH of the soil, the activity of several enzymes (alkaline phosphatase, urease, and dehydrogenase), the nitrogen content (NH4+-N and NO3−-N), and the pakchoi quality (Vc and soluble protein content), while also raising the relative abundance of bacteria that promote plant growth and immobilize metals, such as Streptomyces and Sphingomonas. In conclusion, Hao 2018 reduced the available Pb in soil and pakchoi Pb absorption by increasing the pH and activity of multiple enzymes and regulating microbiome composition in rhizospheric soil.

Distribution of sediment microbial communities and their relationship with surrounding environmental factors in a typical rural river, Southwest China

With rapid urbanization and industrialization, rural rivers in China are facing deterioration in water quality and ecosystem health. Microorganisms living in river sediments are involved in biogeochemical processes, mineralization, and degradation of pollutants. Understanding bacterial community distribution in rural rivers could help evaluate the response of river ecosystems to environmental pollution and understand the river self-purification mechanism. In this study, the relationship between characteristics of sediment microbial communities and the surrounding environmental factors in a typical rural river was analyzed using 16S rRNA gene sequencing technology. The results showed that the dominant bacterial groups in the river sediment were Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Firmicutes, accounting for 83.61% of the total microbial load. Different areas have different sources of pollution which give rise to specific dominant bacteria. The upstream part of the river flows through an agricultural cultivation area where the dominant bacteria were norank_f_Gemmatimonadaceae, Haliangium, and Pseudolabrys, possessing obvious nitrogen- and phosphorus-metabolizing activities. The midstream section flows through an urban area where the dominant bacteria were Marmoricola, Nocardioides, Gaiella, Sphingomonas, norank_f_67-14, Subgroup_10, Agromyces, and Lysobacter, with strong metabolizing activity for toxic pollutants. The dominant bacteria in the downstream part were Clostridium_sensu_stricto_1, norank_f__Bacteroidetes_vadinHA17, Candidatus_Competibacter, and Methylocystis. Redundancy analysis and correlation heatmap analysis showed that environmental factors: ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) in the sediment, and pH, temperature, TN, electrical conductivity (EC), and total dissolved solids (TDS) in the water, significantly affected the bacterial community in the sediment. The PICRUSt2 functional prediction analysis identified that the main function of bacteria in the sediment was metabolism (77.3%), specifically carbohydrate, amino acid, and energy metabolism. These activities are important for degrading organic matter and removing pollutants from the sediments. The study revealed the influence of organic pollutants derived from human activities on the bacterial community composition in the river sediments. It gave a new insight into the relationship between environmental factors and bacterial community distribution in rural watershed ecosystems, providing a theoretical basis for self-purification and bioremediation of rural rivers.

Controlling AMR in the Pig Industry: Is It Enough to Restrict Heavy Metals?

Heavy metals have the potential to influence the transmission of antimicrobial resistance (AMR). However, the effect on AMR caused by heavy metals has not been clearly revealed. In this study, we used a microcosm experiment and metagenomics to examine whether common levels of Cu and Zn in pig manure influence AMR transmission in manured soil. We found that the abundance of 204 ARGs significantly increased after manure application, even though the manure did not contain antibiotic residuals. However, the combined addition of low Cu and Zn (500 and 1000 mg/kg, respectively) only caused 14 ARGs to significantly increase, and high Cu and Zn (1000 and 3000 mg/kg, respectively) caused 27 ARGs to significantly increase. The disparity of these numbers suggested that factors within the manure were the primary driving reasons for AMR transmission, rather than metal amendments. A similar trend was found for biocide and metal resistance genes (BMRGs) and mobile genetic elements (MGEs). This study offers deeper insights into AMR transmission in relation to the effects of manure application and heavy metals at commonly reported levels. Our findings recommend that more comprehensive measures in controlling AMR in the pig industry are needed apart from restricting heavy metal additions.

Comparative genomics provides insights into the potential biocontrol mechanism of two Lysobacter enzymogenes strains with distinct antagonistic activities

Lysobacter enzymogenes has been applied as an abundant beneficial microorganism to control plant disease; however, most L. enzymogenes strains have been mainly reported to control fungal diseases, not bacterial diseases. In this study, two L. enzymogenes strains were characterized, of which CX03 displayed a broad spectrum of antagonistic activities toward multiple bacteria, while CX06 exhibited a broad spectrum of antagonistic activities toward diverse fungi and oomycete, and the whole genomes of the two strains were sequenced and compared. The genome annotation showed that the CX03 genome comprised a 5,947,018 bp circular chromosome, while strain CX06 comprised a circular 6,206,196 bp chromosome. Phylogenetic analysis revealed that CX03 had a closer genetic relationship with L. enzymogenes ATCC29487T and M497-1, while CX06 was highly similar to L. enzymogenes C3. Functional gene annotation analyses of the two L. enzymogenes strains showed that many genes or gene clusters associated with the biosynthesis of different secondary metabolites were found in strains CX03 and CX06, which may be responsible for the different antagonistic activities against diverse plant pathogens. Moreover, comparative genomic analysis revealed the difference in bacterial secretory systems between L. enzymogenes strains CX03 and CX06. In addition, numerous conserved genes related to siderophore biosynthesis, quorum sensing, two-component systems, flagellar biosynthesis and chemotaxis were also identified in the genomes of strains CX03 and CX06. Most reported L. enzymogenes strains were proven mainly to suppress fungi, while CX03 exhibited direct inhibitory activities toward plant bacterial pathogens and showed an obvious role in managing bacterial disease. This study provides a novel understanding of the biocontrol mechanisms of L. enzymogenes, and reveals great potential for its application in plant disease control.

Plasmopara viticola the Causal Agent of Downy Mildew of Grapevine: From Its Taxonomy to Disease Management

Plasmopara viticola (P. viticola, Berk. & M. A. Curtis; Berl. & De Toni) causing grapevine downy mildew is one of the most damaging pathogens to viticulture worldwide. Since its recognition in the middle of nineteenth century, this disease has spread from America to Europe and then to all grapevine-growing countries, leading to significant economic losses due to the lack of efficient disease control. In 1885 copper was found to suppress many pathogens, and is still the most effective way to control downy mildews. During the twentieth century, contact and penetrating single-site fungicides have been developed for use against plant pathogens including downy mildews, but wide application has led to the appearance of pathogenic strains resistant to these treatments. Additionally, due to the negative environmental impact of chemical pesticides, the European Union restricted their use, triggering a rush to develop alternative tools such as resistant cultivars breeding, creation of new active ingredients, search for natural products and biocontrol agents that can be applied alone or in combination to kill the pathogen or mitigate its effect. This review summarizes data about the history, distribution, epidemiology, taxonomy, morphology, reproduction and infection mechanisms, symptoms, host-pathogen interactions, host resistance and control of the P. viticola, with a focus on sustainable methods, especially the use of biocontrol agents.

LC_Glucose-Inhibited Division Protein Is Required for Motility, Biofilm Formation, and Stress Response in Lysobacter capsici X2-3

Glucose-inhibited division protein (GidA) plays a critical role in the growth, stress response, and virulence of bacteria. However, how gidA may affect plant growth-promoting bacteria (PGPB) is still not clear. Our study aimed to describe the regulatory function of the gidA gene in Lysobacter capsici, which produces a variety of lytic enzymes and novel antibiotics. Here, we generated an LC_GidA mutant, MT16, and an LC_GidA complemented strain, Com-16, by plasmid integration. The deletion of LC_GidA resulted in an attenuation of the bacterial growth rate, motility, and biofilm formation of L. capsici. Root colonization assays demonstrated that the LC_GidA mutant showed reduced colonization of wheat roots. In addition, disruption of LC_GidA showed a clear diminution of survival in the presence of high temperature, high salt, and different pH conditions. The downregulated expression of genes related to DNA replication, cell division, motility, and biofilm formation was further validated by real-time quantitative PCR (RT–qPCR). Together, understanding the regulatory function of GidA is helpful for improving the biocontrol of crop diseases and has strong potential for biological applications.

Profiling of Microbial Communities in the Sediments of Jinsha River Watershed Exposed to Different Levels of Impacts by the Vanadium Industry, Panzhihua, China

The mining, smelting, manufacturing, and disposal of vanadium (V) and associated products have caused serious environmental problems. Although the microbial ecology in V-contaminated soils has been intensively studied, the impacted watershed ecosystems have not been systematically investigated. In this study, geochemistry and microbial structure were analyzed along ~30 km of the Jinsha River and its two tributaries across the industrial areas in Panzhihua, one of the primary V mining and production cities in China. Geochemical analyses showed different levels of contamination by metals and metalloids in the sediments, with high degrees of contamination observed in one of the tributaries close to the industrial park. Analyses of the V4 hypervariable region of 16S rRNA genes of the microbial communities in the sediments showed significant decrease in microbial diversity and microbial structure in response to the environmental gradient (e.g., heavy metals, total sulfur, and total nitrogen). Strong association of the taxa (e.g., Thauera, Algoriphagus, Denitromonas, and Fontibacter species) with the metals suggested selection for these potential metal-resistant and/or metabolizing populations. Further co-occurrence network analysis showed that many identified potential metal-mediating species were among the keystone taxa that were closely associated in the same module, suggesting their strong inter-species interactions but relative independence from other microorganisms in the hydrodynamic ecosystems. This study provided new insight into the microbe-environment interactions in watershed ecosystems differently impacted by the V industries. Some of the phylotypes identified in the highly contaminated samples exhibited potential for bioremediation of toxic metals (e.g., V and Cr).

The Perception of Rhizosphere Bacterial Communication Signals Leads to Transcriptome Reprogramming in Lysobacter capsici AZ78, a Plant Beneficial Bacterium

The rhizosphere is a dynamic region governed by complex microbial interactions where diffusible communication signals produced by bacteria continuously shape the gene expression patterns of individual species and regulate fundamental traits for adaptation to the rhizosphere environment. Lysobacter spp. are common bacterial inhabitants of the rhizosphere and have been frequently associated with soil disease suppressiveness. However, little is known about their ecology and how diffusible communication signals might affect their behavior in the rhizosphere. To shed light on the aspects determining rhizosphere competence and functioning of Lysobacter spp., we carried out a functional and transcriptome analysis on the plant beneficial bacterium Lysobacter capsici AZ78 (AZ78) grown in the presence of the most common diffusible communication signals released by rhizosphere bacteria. Mining the genome of AZ78 and other Lysobacter spp. showed that Lysobacter spp. share genes involved in the production and perception of diffusible signal factors, indole, diffusible factors, and N-acyl-homoserine lactones. Most of the tested diffusible communication signals (i.e., indole and glyoxylic acid) influenced the ability of AZ78 to inhibit the growth of the phytopathogenic oomycete Pythium ultimum and the Gram-positive bacterium Rhodococcus fascians. Moreover, RNA-Seq analysis revealed that nearly 21% of all genes in AZ78 genome were modulated by diffusible communication signals. 13-Methyltetradecanoic acid, glyoxylic acid, and 2,3-butanedione positively influenced the expression of genes related to type IV pilus, which might enable AZ78 to rapidly colonize the rhizosphere. Moreover, glyoxylic acid and 2,3-butanedione downregulated tRNA genes, possibly as a result of the elicitation of biological stress responses. On its behalf, indole downregulated genes related to type IV pilus and the heat-stable antifungal factor, which might result in impairment of twitching motility and antibiotic production in AZ78. These results show that diffusible communication signals may affect the ecology of Lysobacter spp. in the rhizosphere and suggest that diffusible communication signals might be used to foster rhizosphere colonization and functioning of plant beneficial bacteria belonging to the genus Lysobacter.

Effects of Heavy Metals/Metalloids and Soil Properties on Microbial Communities in Farmland in the Vicinity of a Metals Smelter

Microorganisms play a fundamental role in biogeochemical cycling and are highly sensitive to environmental factors, including the physiochemical properties of the soils and the concentrations of heavy metals/metalloids. In this study, high-throughput sequencing of the 16S rRNA gene was used to study the microbial communities of farmland soils in farmland in the vicinity of a lead–zinc smelter. Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Gemmatimonadetes were the predominant phyla in the sites of interest. Sphingomonas, Gemmatimonas, Lysobacter, Flavisolibacter, and Chitinophaga were heavy metal-/metalloid-tolerant microbial groups with potential for bioremediation of the heavy metal/metalloid contaminated soils. However, the bacterial diversity was different for the different sites. The contents of heavy metal/metalloid species and the soil properties were studied to evaluate the effect on the soil bacterial communities. The Mantel test revealed that soil pH, total cadmium (T-Cd), and available arsenic played a vital role in determining the structure of the microbial communities. Further, we analyzed statistically the heavy metals/metalloids and the soil properties, and the results revealed that the microbial richness and diversity were regulated mainly by the soil properties, which correlated positively with organic matter and available nitrogen, while available phosphorus and available potassium were negatively correlated. The functional annotation of the prokaryotic taxa (FAPROTAX) method was used to predict the function of the microbial communities. Chemoheterotrophy and airborne chemoheterotrophy of the main microbial community functions were inhibited by soil pH and the heavy metals/metalloids, except in the case of available lead. Mantel tests revealed that T-Cd and available zinc were the dominant factors affecting the functions of the microbial communities. Overall, the research indicated that in contaminated soils, the presence of multiple heavy metals/metalloids, and the soil properties synergistically shaped the structure and function of the microbial communities.

Characterisation of the Antibiotic Profile of Lysobacter capsici AZ78, an Effective Biological Control Agent of Plant Pathogenic Microorganisms

Determining the mode of action of microbial biocontrol agents plays a key role in their development and registration as commercial biopesticides. The biocontrol rhizobacterium Lysobacter capsici AZ78 (AZ78) is able to inhibit a vast array of plant pathogenic oomycetes and Gram-positive bacteria due to the release of antimicrobial secondary metabolites. A combination of MALDI-qTOF-MSI and UHPLC-HRMS/M was applied to finely dissect the AZ78 metabolome and identify the main secondary metabolites involved in the inhibition of plant pathogenic microorganisms. Under nutritionally limited conditions, MALDI-qTOF-MSI revealed that AZ78 is able to release a relevant number of antimicrobial secondary metabolites belonging to the families of 2,5-diketopiperazines, cyclic lipodepsipeptides, macrolactones and macrolides. In vitro tests confirmed the presence of secondary metabolites toxic against Pythium ultimum and Rhodococcus fascians in AZ78 cell-free extracts. Subsequently, UHPLC-HRMS/MS was used to confirm the results achieved with MALDI-qTOF-MSI and investigate for further putative antimicrobial secondary metabolites known to be produced by Lysobacter spp. This technique confirmed the presence of several 2,5-diketopiperazines in AZ78 cell-free extracts and provided the first evidence of the production of the cyclic depsipeptide WAP-8294A2 in a member of L. capsici species. Moreover, UHPLC-HRMS/MS confirmed the presence of dihydromaltophilin/Heat Stable Antifungal Factor (HSAF) in AZ78 cell-free extracts. Due to the production of HSAF by AZ78, cell-free supernatants were effective in controlling Plasmopara viticola on grapevine leaf disks after exposure to high temperatures. Overall, our work determined the main secondary metabolites involved in the biocontrol activity of AZ78 against plant pathogenic oomycetes and Gram-positive bacteria. These results might be useful for the future development of this bacterial strain as the active ingredient of a microbial biopesticide that might contribute to a reduction in the chemical input in agriculture.

Genomic Analysis of the Endophytic Stenotrophomonas Strain 169 Reveals Features Related to Plant-Growth Promotion and Stress Tolerance

Plant-associated Stenotrophomonas isolates have great potential for plant growth promotion, especially under stress conditions, due to their ability to promote tolerance to abiotic stresses such as salinity or drought. The endophytic strain Stenotrophomonas sp. 169, isolated from a field-grown poplar, increased the growth of inoculated in vitro plants, with a particular effect on root development, and was able to stimulate the rooting of poplar cuttings in the greenhouse. The strain produced high amounts of the plant growth-stimulating hormone auxin under in vitro conditions. The comparison of the 16S rRNA gene sequences and the phylogenetic analysis of the core genomes showed a close relationship to Stenotrophomonas chelatiphaga and a clear separation from Stenotrophomonas maltophilia. Whole genome sequence analysis revealed functional genes potentially associated with attachment and plant colonization, growth promotion, and stress protection. In detail, an extensive set of genes for twitching motility, chemotaxis, flagella biosynthesis, and the ability to form biofilms, which are connected with host plant colonization, could be identified in the genome of strain 169. The production of indole-3-acetic acid and the presence of genes for auxin biosynthesis pathways and the spermidine pathway could explain the ability to promote plant growth. Furthermore, the genome contained genes encoding for features related to the production of different osmoprotective molecules and enzymes mediating the regulation of stress tolerance and the ability of bacteria to quickly adapt to changing environments. Overall, the results of physiological tests and genome analysis demonstrated the capability of endophytic strain 169 to promote plant growth. In contrast to related species, strain 169 can be considered non-pathogenic and suitable for biotechnology applications.

Volatile-Mediated Inhibitory Activity of Rhizobacteria as a Result of Multiple Factors Interaction: The Case of Lysobacter capsici AZ78

Plant beneficial rhizobacteria may antagonize soilborne plant pathogens by producing a vast array of volatile organic compounds (VOCs). The production of these compounds depends on the medium composition used for bacterial cell growth. Accordingly, Lysobacter capsici AZ78 (AZ78) grown on a protein-rich medium was previously found to emit volatile pyrazines with toxic activity against soilborne phypathogenic fungi and oomycetes. However, the discrepancy between the quantity of pyrazines in the gaseous phase and the minimum quantity needed to achieve inhibition of plant pathogens observed, lead us to further investigate the volatile-mediated inhibitory activity of AZ78. Here, we show that, besides VOCs, AZ78 cells produce ammonia in increased amounts when a protein-rich medium is used for bacterial growth. The production of this volatile compound caused the alkalinization of the physically separated culture medium where Rhizoctonia solani was inoculated subsequently. Results achieved in this work clearly demonstrate that VOC, ammonia and the growth medium alkalinization contribute to the overall inhibitory activity of AZ78 against R. solani. Thus, our findings suggest that the volatile-mediated inhibitory activity of rhizobacteria in protein-rich substrates can be regarded as a result of multiple factors interaction, rather than exclusively VOCs production.

Volatile Organic Compounds From Lysobacter capsici AZ78 as Potential Candidates for Biological Control of Soilborne Plant Pathogens

The genus Lysobacter includes several bacterial species which show potential for being used in biological control of plant diseases. It was shown recently that several Lysobacter type strains produce volatile organic compounds (VOCs) which controlled the growth of Phytophthora infestans in vitro when the bacteria were grown on a protein rich medium. In the present study, Lysobacter capsici AZ78 (AZ78) has been tested for its potential to produce VOCs that may contribute to the bioactivity against soilborne plant pathogens. To this end, split Petri dish assays of bacterial cultures have been combined with GC-MS measurements with the aim to reveal the identity of the VOCs which inhibit the growth of Pythium ultimum Rhizoctonia solani, and Sclerotinia minor. While AZ78 completely suppressed the growth of P. ultimum and S. minor, the growth of R. solani was still reduced significantly. The GC-MS analysis revealed 22 VOCs to be produced by AZ78, the majority of which were (putatively) identified as mono- and dialkylated methoxypyrazines. Based on additional cultivation and GC-MS experiments, 2,5-dimethylpyrazine, 2-ethyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine were selected as presumable bioactive compounds. Further bioassays employing indirect exposure to standard solutions (1–10 mg per Petri dish) of the synthetic compounds via the gas phase, revealed that each of these pyrazines was able to suppress the growth of the pathogens under investigation. The results of this study highlight the possible future implementation of pyrazine derivatives in the control of soilborne plant diseases and further support the biocontrol potential of L. capsici AZ78.

The rhizosphere signature on the cell motility, biofilm formation and secondary metabolite production of a plant-associated Lysobacter strain

Lysobacter spp. are common bacterial inhabitants of the rhizosphere of diverse plant species. However, the impact of the rhizosphere conditions on their physiology is still relatively understudied. To provide clues on the behaviour of Lysobacter spp. in this ecological niche, we investigated the physiology of L. capsici AZ78 (AZ78), a biocontrol strain isolated from tobacco rhizosphere, on a common synthetic growth medium (LBA) and on a growth medium containing components of the plant rhizosphere (RMA). The presence of a halo surrounding the AZ78 colony on RMA was a first visible effect related to differences in growth medium composition and it corresponded to the formation of a large outer ring. The lower quantity of nutrients available in RMA as compared with LBA was associated to a higher expression of a gene encoding cAMP-receptor-like protein (Clp), responsible for cell motility and biofilm formation regulation. AZ78 cells on RMA were motile, equipped with cell surface appendages and organised in small groups embedded in a dense layer of fibrils. Metabolic profiling by mass spectrometry imaging revealed increased diversity of analytes produced by AZ78 on RMA as compared with LBA. In particular, putative cyclic lipodepsipeptides, polycyclic tetramate macrolactams, cyclic macrolactams and other putative secondary metabolites with antibiotic activity were identified. Overall, the results obtained in this study shed a light on AZ78 potential to thrive in the rhizosphere by its ability to move, form biofilm and release secondary metabolites.

Lysobacter tabacisoli sp. nov., isolated from rhizosphere soil of Nicotiana tabacum L

A Gram-stain-negative, aerobic, rod-shaped bacterium, designated strain C8-1T, was isolated from the rhizosphere soil of Nicotiana tabacum L. collected from Kunming, south-west China. The cells showed oxidase-positive and catalase-positive reactions. Growth was observed at 10-40 °C, at pH 6.0-8.0 and in the presence of up to 1 % (w/v) NaCl, with optimal growth at 30 °C and pH 7.0. The predominant isoprenoid quinone was Q-8. The major fatty acids were identified as iso-C15 : 0, iso-C17 : 0 and iso-C17 : 1ω9c. The cellular polar lipids contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, five unidentified phospholipids and two unidentified aminophospholipids. The genomic DNA G+C content was 70.7 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain C8-1T should be assigned to the genus Lysobacter. 16S rRNA gene sequence similarity analysis showed that strain C8-1T was closely related to Lysobacter cavernae YIM C01544T (98.6 %), Lysobacter soli DCY21T (97.6 %), Lysobacter panacisoli CJ29T (97.3 %), Lysobacter firmicutimachus PB-6250T (97.3 %), Lysobacter niastensis GH41-7T (97.3 %) and Lysobacter gummosus KCTC 12132T (97.1 %). DNA-DNA hybridization data indicated that the isolate may represent a novel genomic species belonging to the genus Lysobacter. Polyphasic taxonomic characteristics indicated that strain C8-1T represents a novel species of the genus Lysobacter, for which the name Lysobacter tabacisoli sp. nov. is proposed. The type strain is C8-1T (=KCTC 62034T=CGMCC 1.16271T) .

Diversity of Bacterial Biota in Capnodis tenebrionis (Coleoptera: Buprestidae) Larvae

The bacterial biota in larvae of Capnodis tenebrionis, a serious pest of cultivated stone-fruit trees in the West Palearctic, was revealed for the first time using the MiSeq platform. The core bacterial community remained the same in neonates whether upon hatching or grown on peach plants or an artificial diet, suggesting that C. tenebrionis larvae acquire much of their bacterial biome from the parent adult. Reads affiliated with class levels Gammaproteobacteria and Alphaproteobacteria (phylum Proteobacteria ca. 86%), and Actinobacteria (ca. 14%) were highly abundant. Most diverse reads belong to the families Xanthomonadaceae (50%), Methylobacteriaceae (20%), Hyphomicrobiaceae (9%), Micrococcaceae (7%) and Geodermatophilaceae (4.5%). About two-thirds of the reads are affiliated with the genera Lysobacter, Microvirga, Methylobacterium, and Arthrobacter, which encompass species displaying cellulolytic and lipolytic activities. This study provides a foundation for future studies to elucidate the roles of bacterial biota in C. tenebrionis.

Marchantia liverworts as a proxy to plants' basal microbiomes

Microbiomes influence plant establishment, development, nutrient acquisition, pathogen defense, and health. Plant microbiomes are shaped by interactions between the microbes and a selection process of host plants that distinguishes between pathogens, commensals, symbionts and transient bacteria. In this work, we explore the microbiomes through massive sequencing of the 16S rRNA genes of microbiomes two Marchantia species of liverworts. We compared microbiomes from M. polymorpha and M. paleacea plants collected in the wild relative to their soils substrates and from plants grown in vitro that were established from gemmae obtained from the same populations of wild plants. Our experimental setup allowed identification of microbes found in both native and in vitro Marchantia species. The main OTUs (97% identity) in Marchantia microbiomes were assigned to the following genera: Methylobacterium, Rhizobium, Paenibacillus, Lysobacter, Pirellula, Steroidobacter, and Bryobacter. The assigned genera correspond to bacteria capable of plant-growth promotion, complex exudate degradation, nitrogen fixation, methylotrophs, and disease-suppressive bacteria, all hosted in the relatively simple anatomy of the plant. Based on their long evolutionary history Marchantia is a promising model to study not only long-term relationships between plants and their microbes but also the transgenerational contribution of microbiomes to plant development and their response to environmental changes.

The bacterial community structure and functional profile in the heavy metal contaminated paddy soils, surrounding a nonferrous smelter in South Korea

The pollution of agricultural soils by the heavy metals affects the productivity of the land and has an impact on the quality of the surrounding ecosystems. This study investigated the bacterial community structure in the heavy metal contaminated sites along a smelter and a distantly located paddy field to elucidate the factors that are related to the alterations of the bacterial communities under the conditions of heavy metal pollution. Among the study sites, the bacterial communities in the soil did not show any significant differences in their richness and diversity. The soil bacterial communities at the three study sites were distinct from one another at each site, possessing a distinct set of bacterial phylotypes. Among the study sites, significant changes were observed in the abundances of the bacterial phyla and genera. The variations in the bacterial community structure were mostly related to the general soil properties at the phylum level, while at the finer taxonomic levels, the concentrations of arsenic (As) and lead (Pb) were the significant factors, affecting the community structure. The relative abundances of the genera Desulfatibacillum and Desulfovirga were negatively correlated to the concentrations of As, Pb, and cadmium (Cd) in the soil, while the genus Bacillus was positively correlated to the concentrations of As and Cd. According to the results of the prediction of bacterial community functions, the soil bacterial communities of the heavy metal polluted sites were characterized by the more abundant enzymes involved in DNA replication and repair, translation, transcription, and the nucleotide metabolism pathways, while the amino acid and lipid metabolism, as well as the biodegradation potential of xenobiotics, were reduced. Our results showed that the adaptation of the bacterial communities to the heavy metal contamination was predominantly attributed to the replacement process, while the changes in community richness were linked to the variations in the soil pH values.

The impact of the omics era on the knowledge and use of Lysobacter species to control phytopathogenic micro-organisms

Omics technologies have had a tremendous impact on underinvestigated genera of plant disease biocontrol agents such as Lysobacter. Strong evidence of the association between Lysobacter spp. and the rhizosphere has been obtained through culture-independent methods, which has also contributed towards highlighting the relationship between Lysobacter abundance and soil suppressiveness. It is conceivable that the role played by Lysobacter spp. in soil suppressiveness is related to their ability to produce an impressive array of lytic enzymes and antibiotics. Indeed, genomics has revealed that biocontrol Lysobacter strains share a vast number of genes involved in antagonism activities, and the molecular pathways underlying how Lysobacter spp. interact with the environment and other micro-organisms have been depicted through transcriptomic analysis. Furthermore, omics technologies shed light on the regulatory pathways governing cell motility and the biosynthesis of antibiotics. Overall, the results achieved so far through omics technologies confirm that the genus Lysobacter is a valuable source of novel biocontrol agents, paving the way for studies aimed at making their application in field conditions more reliable.

Growth media affect the volatilome and antimicrobial activity against Phytophthora infestans in four Lysobacter type strains

Bacterial volatile organic compounds (VOCs) play important ecological roles in soil microbial interactions. Lysobacter spp. are key determinants of soil suppressiveness against phytopathogens and the production of non-volatile antimicrobial metabolites has been extensively characterised. However, the chemical composition and antagonistic properties of the Lysobacter volatilome have been poorly investigated. In this work, VOC emission profiles of four Lysobacter type strains grown on a sugar-rich and a protein-rich medium were analysed using solid-phase microextraction gas chromatography-mass spectrometry and proton transfer reaction-time of flight-mass spectrometry. Lysobacter antibioticus, L. capsici, L. enzymogenes and L. gummosus type strains were recognised according to their volatilome assessed using both headspace mass spectrometry methods Moreover, the chemical profiles and functional properties of the Lysobacter volatilome differed according to the growth medium, and a protein-rich substrate maximised the toxic effect of the four Lysobacter type strains against Phytophthora infestans. Antagonistic (pyrazines, pyrrole and decanal) and non-antagonistic (delta-hexalactone and ethanol) VOCs against Ph. infestans or putative plant growth stimulator compounds (acetoin and indole) were mainly emitted by Lysobacter type strains grown on protein- and sugar-rich media respectively. Thus nutrient availability under soil conditions could affect the aggressiveness of Lysobacter spp. and possibly optimise interactions of these bacterial species with the other soil inhabitants.

Effects of biocide treatments on the biofilm community in Domitilla's catacombs in Rome

Different types of biofilms are widespread on lithic faces of the Catacombs of Domitilla (Rome, Italy) due to the favorable microclimatic conditions (temperature, high RH% and low irradiance). The biofilm, once established, becomes particularly dangerous due to the coverage of valuable surfaces causing spoilage, softening of materials and mineral precipitation. It is common practice to treat these surfaces with biocides in order to eradicate the microorganisms present. The aim of the present research was to compare the changes occurring to the microbial community present in the biofilm in one site of the Catacombs of Domitilla (CD15) before and after a biocide treatment (a mixture of quaternary ammonium compounds and octylisothiazolone, OIT), applied for a one month period. A multistep approach was followed, based on microscopy, cultural methods and molecular techniques (f-ITS and 16S rDNA sequencing), for the phenotypic and genetic analysis of the culturable microbial population. Our results highlighted that the biocide treatments had little effect against cyanobacteria, while the bacterial population increased in numbers but changed drastically in terms of diversity. In fact, some bacteria proliferate at the expense of the organic matter released by dead microorganisms as demonstrated by laboratory tests. Further, our data describe how the microbial interaction can have different responses depending on the favorable conditions for one kind of microorganism in respect to the others. This study exemplifies the real risks of applying biocide treatments on complex microbial communities and pinpoints the necessity of subjecting treatments to monitoring and reassessment. Moreover, the work showed the potential of bacteria isolated after the treatment for use, under controlled conditions, in combatting unwanted microbial growth in that they possess a positive tropism toward stressed microorganisms and high hydrolytic enzymatic activity against cell components (e.g. cellulose, chitin and pectin). A tentative protocol is proposed.

Pea Broth Enhances the Biocontrol Efficacy of Lysobacter capsici AZ78 by Triggering Cell Motility Associated with Biogenesis of Type IV Pilus

Bacterial cells can display different types of motility, due to the presence of external appendages such as flagella and type IV pili. To date, little information on the mechanisms involved in the motility of the Lysobacter species has been available. Recently, L. capsici AZ78, a biocontrol agent of phytopathogenic oomycetes, showed the ability to move on jellified pea broth. Pea broth medium improved also the biocontrol activity of L. capsici AZ78 against Plasmopara viticola under greenhouse conditions. Noteworthy, the quantity of pea residues remaining on grapevine leaves fostered cell motility in L. capsici AZ78. Based on these results, this unusual motility related to the composition of the growth medium was investigated in bacterial strains belonging to several Lysobacter species. The six L. capsici strains tested developed dendrite-like colonies when grown on jellified pea broth, while the development of dendrite-like colonies was not recorded in the media commonly used in motility assays. To determine the presence of genes responsible for biogenesis of the flagellum and type IV pili, the genome of L. capsici AZ78 was mined. Genes encoding structural components and regulatory factors of type IV pili were upregulated in L. capsici AZ78 cells grown on the above-mentioned medium, as compared with the other tested media. These results provide new insight into the motility mechanism of L. capsici members and the role of type IV pili and pea compounds on the epiphytic fitness and biocontrol features of L. capsici AZ78.

Lysobacter cavernae sp. nov., a novel bacterium isolated from a cave sample

A Gram-staining negative, aerobic, rod-shaped bacterium, designated YIM C01544(T), was isolated from a soil sample collected from Sigangli Cave, Yunnan province, South-West China. The strain was able to grow over a range of temperatures (4-30 °C), pH (6.0-10.0) and NaCl concentration (0-2 %, w/v). Comparative 16S rRNA gene sequence analysis revealed that strain YIM C01544(T) should be a member of the genus Lysobacter. The strain is closely related to Lysobacter niastensis GH41-7(T) (97.6 %), Lysobacter soli DCY21(T) (97.5 %), Lysobacter enzymogenes DSM 2043(T) (97.3 %), Lysobacter antibioticus DSM 2044(T) (97.1 %) and Lysobacter panacisoli CJ29(T) (97.1 %). The genomic DNA relatedness values (<47 %) as indicated by DNA-DNA hybridization studies were below the threshold limit for characterization of new bacterial species. The chemotaxonomic features of the new isolate include diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids and two unidentified polar lipids as its characteristic polar lipids and Q-8 as the only quinone. The major fatty acids detected were iso-C15:0 and iso-C17:1 ω9c. The DNA G + C content of the strain was determined to be 64.9 mol %. Based on the data from phenotypic, chemotaxonomic and molecular studies, strain YIM C01544(T) merits recognition as novel species in the genus Lysobacter for which the name Lysobacter cavernae sp. nov. is proposed. The type strain of Lysobacter cavernae is YIM C01544(T) (= KCTC 42875(T) = DSM 101561(T) = CPCC 100816(T)).