Bacterial pectate lyases, structural and functional diversity

Controlling soft rot of green pepper by bacteriocin paracin wx3 and its effect on storage quality of green pepper

A bacteriocin paracin wx3 was investigated as a candidate of natural preservative to control green pepper soft rot. Firstly, paracin wx3 was heterologously expressed in Pichia pastoris X33 with an improved yield of 0.537 g/L. Its size and amino acid sequence were confirmed by Tricine-SDS-PAGE and LC-MS/MS. Then, result of antibacterial activity showed that its MIC value against Pectobacterium carotovorum was 16 μg/mL. In vitro, paracin wx3 completely killed the pathogen at high concentrations ≥8 × MIC. In vivo, disease incidence of green pepper soft rot was decreased from 90% (control) to <2% (8 × MIC). Subsequently, results of action mode showed that paracin wx3 inhibited the growth of pathogen by pore-formation on cell membrane. Last, paracin wx3 treatment reduced losses of weight, firmness, total soluble solid, Vc of green pepper during storage. It also inhibited the production of soft rot volatile p-xylene, 1-butanol, 2-methyl-2-propanol, 3-hydroxybutan-2-one-D, 2-pentyl furan, butanal, etc.

Unveiling novel insights into Bacillus velezensis 16B pectin lyase for improved fruit juice processing

Microbial pectinolytic enzymes are important in various industries, particularly food processing. This study focuses on uncovering insights into a novel pectin lyase, BvPelB, from Bacillus velezensis 16B, with the aim of enhancing fruit juice processing. The study examines the structural and functional characteristics of pectinolytic enzyme, underscoring the critical nature of substrate specificity and enzymatic reaction mechanisms. BvPelB was successfully expressed and purified, exhibiting robust activity under alkaline conditions and thermal stability. Structural analysis revealed similarities with other pectin lyases, despite limited sequence identity. Biochemical characterization showed BvPelB's preference for highly methylated pectins and its endo-acting mode of cleavage. Treatment with BvPelB significantly increased juice yield and clarity without generating excessive methanol, making it a promising candidate for fruit juice processing. Overall, this study provides valuable insights into the enzymatic properties of BvPelB and its potential industrial applications in improving fruit juice processing efficiency and quality.

Advancements in enzyme immobilization on magnetic nanomaterials: toward sustainable industrial applications

Enzymes are widely used in biofuels, food, and pharmaceuticals. The immobilization of enzymes on solid supports, particularly magnetic nanomaterials, enhances their stability and catalytic activity. Magnetic nanomaterials are chosen for their versatility, large surface area, and superparamagnetic properties, which allow for easy separation and reuse in industrial processes. Researchers focus on the synthesis of appropriate nanomaterials tailored for specific purposes. Immobilization protocols are predefined and adapted to both enzymes and support requirements for optimal efficiency. This review provides a detailed exploration of the application of magnetic nanomaterials in enzyme immobilization protocols. It covers methods, challenges, advantages, and future perspectives, starting with general aspects of magnetic nanomaterials, their synthesis, and applications as matrices for solid enzyme stabilization. The discussion then delves into existing enzymatic immobilization methods on magnetic nanomaterials, highlighting advantages, challenges, and potential applications. Further sections explore the industrial use of various enzymes immobilized on these materials, the development of enzyme-based bioreactors, and prospects for these biocatalysts. In summary, this review provides a concise comparison of the use of magnetic nanomaterials for enzyme stabilization, highlighting potential industrial applications and contributing to manufacturing optimization.

Untargeted metabolomics coupled with genomics in the study of sucrose and xylose metabolism in Pectobacterium betavasculorum

Introduction

Pectobacterium betavasculorum is a member of the Pectobacerium genus that inhabits a variety of niches and is found in all climates. Bacteria from the Pectobacterium genus can cause soft rot disease on various plants due to the secretion of plant cell wall degrading enzymes (PCWDEs). The species P. betavasculorum is responsible for the vascular necrosis of sugar beet and soft rot of many vegetables. It also infects sunflowers and artichokes. The main sugar present in sugar beet is sucrose while xylose is one of the main sugars in artichoke and sunflower.

Methods

In our work, we applied metabolomic studies coupled with genomics to investigate the metabolism of P. betavasculorum in the presence of xylose and sucrose as the only carbon source. The ability of the strains to use various sugars as the only carbon source were confirmed by the polypyridyl complex of Ru(II) method in 96-well plates.

Results

Our studies provided information on the metabolic pathways active during the degradation of those substrates. It was observed that different metabolic pathways are upregulated in the presence of xylose in comparison to sucrose.

Discussion

The presence of xylose enhances extracellular metabolism of sugars and glycerol as well as stimulates EPS and IPS synthesis. In contrast, in the presence of sucrose the intensive extracellular metabolism of amines and amino acids is promoted.

Comparative genomic and transcriptome analyses of two Pectobacterium brasiliense strains revealed distinct virulence determinants and phenotypic features

Potato soft rot caused by Pectobacterium spp. are devastating diseases of potato which cause severe economic losses worldwide. Pectobacterium brasiliense is considered as one of the most virulent species. However, the virulence mechanisms and pathogenicity factors of this strain have not been fully elucidated. Here, through pathogenicity screening, we identified two Pectobacterium brasiliense isolates, SM and DQ, with distinct pathogenicity levels. SM exhibits higher virulence compared to DQ in inducing aerial stem rot, blackleg and tuber soft rot. Our genomic and transcriptomic analyses revealed that SM encodes strain specific genes with regard to plant cell wall degradation and express higher level of genes associated with bacterial motility and secretion systems. Our plate assays verified higher pectinase, cellulase, and protease activities, as well as fast swimming and swarming motility in SM. Importantly, a unique endoglucanase S specific to SM was identified. Expression of this cellulase in DQ greatly enhances its virulence compared to wild type strain. Our study sheds light on possible determinants causing different pathogenicity of Pectobacterium brasiliense species with close evolutionary distance and provides new insight into the direction of genome evolution in response to host variation and environmental stimuli.

Description of a new genus of the Pectobacteriaceae family isolated from water in coastal brackish wetlands of the French Camargue region, Prodigiosinella gen. nov., including the new species Prodigiosinella aquatilis sp. nov

The Pectobacteriaceae family comprises plant pathogens able to provoke diverse diseases, including plant maceration due to the production of pectinases disrupting the plant cell wall. To better understand their diversity, a survey of pectinolytic bacteria was performed in brackish lakes of the French region La Camargue near the Mediterranean Sea. The genome of six atypical isolates was sequenced; their size is around 4.8 to 5.0 Mb, including a plasmid of 59 to 61 kb; their G+C values range from 49.1 to 49.3 mol%. Phylogenetic analyses indicated that the novel strains form a new clade of Pectobacteriaceae that branches at the basis of the group encompassing the genera Lonsdalea, Musicola, and Dickeya. Based on phenotypic, genomic and phylogenetic characteristics, we propose the creation of a new genus with the name Prodigiosinella gen. nov. Both the phenotypic and phylogenetic analyses separated the strains into two distinct subgroups, G1 and G2. The type strain LS101T (CFBP 8826T = LMG 32072T) and strain CE70 (CFBP 9054 = LMG 32867) are representative G1 and G2 members, respectively. Three genomic methods were used to analyze DNA-DNA relatedness: digital DNA-DNA hybridization (isDDH), average nucleotide identity (ANI), and genome alignment fraction (AF). They revealed a close relationship between genomes of the two groups, supporting their appurtenance to a same species for which we propose the name Prodigiosinella aquatilis sp. nov. Four strains previously designated as Serratia sp. (ATCC 39006), Brenneria "ulupoensis" (K61) or Erwinia sp. (MK01 and MK09) belong to the new genus Prodigiosinella.

A novel pectate lyase with high specific activity from Bacillus sp. B58-2: Gene cloning, heterologous expression and use in ramie degumming

Pectinase plays a crucial role in ramie degumming. A gene encoding a putative pectate lyase from Bacillus sp. strain B58-2 was cloned and heterologously expressed in Escherichia coli. The amplified gene BvelPL1 encoded a mature protein of 400 amino acids. BvelPL1 shared the highest amino acid sequence identity (78.75%) with the enzymatically characterized pectate lyase Pel from Bacillus subtilis strain RCK (GenBank: AFH66771.1). The purified recombinant enzyme rBvelPL1-Ec exhibited a maximum specific activity of 2433.26 U/mg at pH 8.5 and 50 °C towards polygalacturonic acid. This specific activity was higher than that of most reported pectate lyases. Remarkably, the enzymatic activity of rBvelPL1-Ec increased by 23.28 times in the presence of 0.4 mM calcium ion. The effect of calcium ion on promoting the enzymatic activity of rBvelPL1-Ec was greater than that for all reported pectate lyases. After degumming with rBvelPL1-Ec, a weight loss of 21.27 ± 1.17% of circled ramie fibers was obtained, and the surfaces of the ramie fibers became smoother. Moreover, a weight loss of 30.47 ± 0.46% was obtained through enzymatic treated and subsequent NaOH treated circled ramie fibers. The excellent performance in degumming suggests that rBvelPL1-Ec may serve as a promising biocatalyst in the textile industry.

Cell surface architecture of the cultivated DPANN archaeon Nanobdella aerobiophila

The DPANN archaeal clade includes obligately ectosymbiotic species. Their cell surfaces potentially play an important role in the symbiotic interaction between the ectosymbionts and their hosts. However, little is known about the mechanism of ectosymbiosis. Here, we show cell surface structures of the cultivated DPANN archaeon Nanobdella aerobiophila strain MJ1T and its host Metallosphaera sedula strain MJ1HA, using a variety of electron microscopy techniques, i.e., negative-staining transmission electron microscopy, quick-freeze deep-etch TEM, and 3D electron tomography. The thickness, unit size, and lattice symmetry of the S-layer of strain MJ1T were different from those of the host archaeon strain MJ1HA. Genomic and transcriptomic analyses highlighted the most highly expressed MJ1T gene for a putative S-layer protein with multiple glycosylation sites and immunoglobulin-like folds, which has no sequence homology to known S-layer proteins. In addition, genes for putative pectin lyase- or lectin-like extracellular proteins, which are potentially involved in symbiotic interaction, were found in the MJ1T genome based on in silico 3D protein structure prediction. Live cell imaging at the optimum growth temperature of 65°C indicated that cell complexes of strains MJ1T and MJ1HA were motile, but sole MJ1T cells were not. Taken together, we propose a model of the symbiotic interaction and cell cycle of Nanobdella aerobiophila.IMPORTANCEDPANN archaea are widely distributed in a variety of natural and artificial environments and may play a considerable role in the microbial ecosystem. All of the cultivated DPANN archaea so far need host organisms for their growth, i.e., obligately ectosymbiotic. However, the mechanism of the ectosymbiosis by DPANN archaea is largely unknown. To this end, we performed a comprehensive analysis of the cultivated DPANN archaeon, Nanobdella aerobiophila, using electron microscopy, live cell imaging, transcriptomics, and genomics, including 3D protein structure prediction. Based on the results, we propose a reasonable model of the symbiotic interaction and cell cycle of Nanobdella aerobiophila, which will enhance our understanding of the enigmatic physiology and ecological significance of DPANN archaea.

Targeted metabolite profiling of Salvia rosmarinus Italian local ecotypes and cultivars and inhibitory activity against Pectobacterium carotovorum subsp. carotovorum

Introduction

The development of agriculture in terms of sustainability and low environmental impact is, at present, a great challenge, mainly in underdeveloped and marginal geographical areas. The Salvia rosmarinus "Eretto Liguria" ecotype is widespread in Liguria (Northwest Italy), and farmers commonly use it by for cuttings and for marketing. In the present study, this ecotype was characterized in comparison with other cultivars from the same geographical region and Campania (Southern Italy), with a view to application and registration processes for the designation of protected geographical indications. Moreover, the possibility of using the resulting biomass after removing cuttings or fronds as a source of extracts and pure compounds to be used as phytosanitary products in organic farming was evaluated. Specifically, the potential of rosemary extracts and pure compounds to prevent soft rot damage was then tested.

Methods

A targeted NMR metabolomic approach was employed, followed by multivariate analysis, to characterize the rosemary accessions. Bacterial soft rot assay and disk diffusion test were carried out to evaluate the activity of extracts and isolated compounds against Pectobacterium carotovorum subsp. carotovorum. Enzymatic assay was performed to measure the in vitro inhibition of the pectinase activity produced by the selected pathogen. Molecular docking simulations were used to explore the possible interaction of the selected compounds with the pectinase enzymes.

Results and Discussion

The targeted metabolomic analysis highlighted those different geographical locations can influence the composition and abundance of bioactive metabolites in rosemary extracts. At the same time, genetic factors are important when a single geographical area is considered. Self-organizing maps (SOMs) showed that the accessions of "Eretto Liguria" appeared well characterized when compared to the others and had a good content in specialized metabolites, particularly carnosic acid. Soft rotting Enterobacteriaceae belonging to the Pectobacterium genus represent a serious problem in potato culture. Even though rosemary methanolic extracts showed a low antibacterial activity against a strain of Pectobacterium carotovorum subsp. carotovorum in the disk diffusion test, they showed ability in reducing the soft rot damage induced by the bacterium on potato tissue. 7-O-methylrosmanol, carnosol and isorosmanol appeared to be the most active components. In silico studies indicated that these abietane diterpenoids may interact with P. carotovorum subsp. carotovorum pectate lyase 1 and endo-polygalacturonase, thus highlighting these rosemary components as starting points for the development of agents able to prevent soft rot progression.

Universal microbial reworking of dissolved organic matter along environmental gradients

Soils are losing increasing amounts of carbon annually to freshwaters as dissolved organic matter (DOM), which, if degraded, can offset their carbon sink capacity. However, the processes underlying DOM degradation across environments are poorly understood. Here we show DOM changes similarly along soil-aquatic gradients irrespective of environmental differences. Using ultrahigh-resolution mass spectrometry, we track DOM along soil depths and hillslope positions in forest catchments and relate its composition to soil microbiomes and physico-chemical conditions. Along depths and hillslopes, we find carbohydrate-like and unsaturated hydrocarbon-like compounds increase in abundance-weighted mass, and the expression of genes essential for degrading plant-derived carbohydrates explains >50% of the variation in abundance of these compounds. These results suggest that microbes transform plant-derived compounds, leaving DOM to become increasingly dominated by the same (i.e., universal), difficult-to-degrade compounds as degradation proceeds. By synthesising data from the land-to-ocean continuum, we suggest these processes generalise across ecosystems and spatiotemporal scales. Such general degradation patterns can help predict DOM composition and reactivity along environmental gradients to inform management of soil-to-stream carbon losses.

Complete genome sequence of carotenoid-producing Aestuariibaculum lutulentum L182T isolated from the tidal sediment

Aestuariibaculum lutulentum L182T (= KCTC 92530T = MCCC 1K08065T) was isolated from the tidal sediment collected in Beihai, People's Republic of China. The genome was sequenced and consisted of a single chromosome with the size of 3,782,725 bp and DNA G + C content of 35.1%. Genomic annotations demonstrated that it encoded 12 rRNA genes, 56 tRNA genes and 3210 ORFs. The percentages of ORFs assigned to CAZy, COG, and KEGG databases were 5.5, 86.2 and 45.5%, respectively. Comparative genomic analysis indicated that the pan- and core-genomes of the genus Aestuariibaculum consisted of 4826 and 2257 orthologous genes, respectively. Carbohydrate-active enzyme annotations of the genus Aestuariibaculum genomes revealed that they shared three polysaccharide lyase (PL) families including PL1, PL22 and PL42. Meanwhile, one carotenoid biosynthetic gene cluster related to biosynthesizing flexixanthin was found in the genus Aestuariibaculum. Furthermore, the core-genome of the genus Aestuariibaculum showed that this genus played a role in cleaving pectate, degrading ulvan, and biosynthesizing carotenoids. This study is a complete genomic report of the genus Aestuariibaculum and broadens understandings of its ecological roles and biotechnological applications.

Two species with a peculiar evolution within the genus Pectobacterium suggest adaptation to a new environmental niche

Historically, research on Soft Rot Pectobacteriacea (SRP) has focused on economically important crops and ornamentals and knowledge of these bacteria outside the plant context remains poorly investigated. Recently, two closely related species Pectobacterium aquaticum and Pectobacterium quasiaquaticum were isolated from water and have not been isolated from any plant yet. To identify the distinctive characteristics of these two species, we performed a comparative genomic analysis of 80 genomes representing 19 Pectobacterium species and performed an evolutionary reconstruction. Both water species underwent a reduction in genome size associated with a high pseudogene content. A high gene loss was predicted at the emergence of both species. Among the 199 gene families missing from both P. aquaticum and P. quasiaquaticum genomes but present in at least 80% of other Pectobacterium genomes, COG analysis identified many genes involved in nutrient transport systems. In addition, many type II secreted proteins were also missing in both species. Phenotypic analysis revealed that both species had reduced pectinolytic activity, a biofilm formation defect, were highly motile and had reduced virulence on several plants. These genomic and phenotypic data suggest that the ecological niche of P. aquaticum and P. quasiaquaticum may differ from that of other Pectobacterium species.

Pectobacterium carotovorum Subsp. brasiliense Causing Soft Rot in Eggplant in Xinjiang, China

An outbreak of stem rot in eggplants was observed in Heshuo County, Xinjiang, during winter 2021-2022 in about 12-35% of the eggplants in the region (about 40 hm2). The infected tissues yielded a total of four bacterial strains, which were subsequently subjected to physiological and biochemical assays as well as molecular identification. Based on these analyses, the pathogen was identified as Pectobacterium carotovorum subsp. brasiliense. The pathogenicity was confirmed through the fulfillment of Koch's postulates. The host range test confirmed the broad spectrum of species susceptible to infection by the strains. This study represents the first case of infection caused by P. carotovorum subsp. brasiliense resulting in stem rot in eggplant.

Diverse signatures of convergent evolution in cacti-associated yeasts

Many distantly related organisms have convergently evolved traits and lifestyles that enable them to live in similar ecological environments. However, the extent of phenotypic convergence evolving through the same or distinct genetic trajectories remains an open question. Here, we leverage a comprehensive dataset of genomic and phenotypic data from 1,049 yeast species in the subphylum Saccharomycotina (Kingdom Fungi, Phylum Ascomycota) to explore signatures of convergent evolution in cactophilic yeasts, ecological specialists associated with cacti. We inferred that the ecological association of yeasts with cacti arose independently ~17 times. Using machine-learning, we further found that cactophily can be predicted with 76% accuracy from functional genomic and phenotypic data. The most informative feature for predicting cactophily was thermotolerance, which is likely associated with duplication and altered evolutionary rates of genes impacting the cell envelope in several cactophilic lineages. We also identified horizontal gene transfer and duplication events of plant cell wall-degrading enzymes in distantly related cactophilic clades, suggesting that putatively adaptive traits evolved through disparate molecular mechanisms. Remarkably, multiple cactophilic lineages and their close relatives are emerging human opportunistic pathogens, suggesting that the cactophilic lifestyle-and perhaps more generally lifestyles favoring thermotolerance-may preadapt yeasts to cause human disease. This work underscores the potential of a multifaceted approach involving high throughput genomic and phenotypic data to shed light onto ecological adaptation and highlights how convergent evolution to wild environments could facilitate the transition to human pathogenicity.

A genome-wide association study reveals that epistasis underlies the pathogenicity of Pectobacterium

Pectobacterium spp. are important bacterial pathogens that cause soft rot symptoms in various crops. However, their mechanism of pathogenicity requires clarity to help control their infections. Here, genome-wide association studies (GWAS) were conducted by integrating genomic data and measurements of two phenotypes (virulence and cellulase activity) for 120 various Pectobacterium strains in order to identify the genetic basis of their pathogenicity. An artificial intelligence-based software program was developed to automatically measure lesion areas on Chinese cabbage, thereby facilitating accurate and rapid data collection for virulence phenotypes for use in GWAS analysis. The analysis discovered 428 and 158 loci significantly associated with Pectobacterium virulence (lesion area) and cellulase activity, respectively. In addition, 1,229 and 586 epistasis loci pairs were identified for the virulence and cellulase activity phenotypes, respectively. Among them, the AraC transcriptional regulator exerted epistasis effects with another three nutrient transport-related genes in pairs contributing to the virulence phenotype, and their epistatic effects were experimentally confirmed for one pair with knockout mutants of each single gene and double gene. This study consequently provides valuable insights into the genetic mechanism underlying Pectobacterium spp. pathogenicity. IMPORTANCE Plant diseases and pests are responsible for the loss of up to 40% of food crops, and annual economic losses caused by plant diseases reach more than $220 billion. Fighting against plant diseases requires an understanding of the pathogenic mechanisms of pathogens. This study adopted an advanced approach using population genomics integrated with virulence-related phenotype data to investigate the genetic basis of Pectobacterium spp., which causes serious crop losses worldwide. An automated software program based on artificial intelligence was developed to measure the virulence phenotype (lesion area), which greatly facilitated this research. The analysis predicted key genomic loci that were highly associated with virulence phenotypes, exhibited epistasis effects, and were further confirmed as critical for virulence with mutant gene deletion experiments. The present study provides new insights into the genetic determinants associated with Pectobacterium pathogenicity and provides a valuable new software resource that can be adapted to improve plant infection measurements.

Pectobacterium jejuense sp. nov. Isolated from Cucumber Stem Tissue

A single Pectobacterium-like strain named 13-115T was isolated from a specimen of diseased cucumber stem tissue collected on Jeju Island, South Korea. The strain presented a rod-like shape and was negative for Gram staining. When grown on R2A medium at 25 °C, strain 13-115T formed round, convex and white colonies. This strain showed growth at temperatures ranging from 10 to 30 °C and tolerated a pH range of 6-9. The strain could also tolerate NaCl concentrations up to 5%. Analysis of the 16S rRNA gene sequence revealed that strain 13-115T exhibited similarity of over 99% with Pectobacterium brasiliense, P. carotovorum, P. polaris, and P. parvum. By conducting multilocus sequence analyses using dnaX, leuS, and recA genes, a separate phylogenetic lineage was discovered between strain 13-115T and other members of the genus Pectobacterium. Moreover, the strain showed relatively low in silico DNA-DNA hybridization (<60.6%) and average nucleotide identity (ANI) (<94.9%) values with recognized Pectobacterium species. The isolate has a genome size of 5,069,478 bp and a genomic G + C content of 52.04 mol%. Major fatty acids identified in the strain included C16:0 (28.99%), summed feature 3 (C16:1 ω7c and/or C16:1 ω6c; 28.85%), and C18:1 ω7c (19.01%). Pathogenicity assay confirmed that the novel strain induced soft rot symptoms in cucumber plants and Koch's postulates were fulfilled. Molecular analysis and phenotypic data indicated that strain 13-115T could be classified as a new species within the Pectobacterium genus, which has been named Pectobacterium jejuense. The type strain is 13-115T (= KCTC 92800T = JCM 35940T).

MarR Family Transcriptional Regulators and Their Roles in Plant-Interacting Bacteria

The relationship between plants and associated soil microorganisms plays a major role in ecosystem functioning. Plant-bacteria interactions involve complex signaling pathways regulating various processes required by bacteria to adapt to their fluctuating environment. The establishment and maintenance of these interactions rely on the ability of the bacteria to sense and respond to biotic and abiotic environmental signals. In this context, MarR family transcriptional regulators can use these signals for transcriptional regulation, which is required to establish adapted responses. MarR-like transcriptional regulators are essential for the regulation of the specialized functions involved in plant-bacteria interactions in response to a wide range of molecules associated with the plant host. The conversion of environmental signals into changes in bacterial physiology and behavior allows the bacteria to colonize the plant and ensure a successful interaction. This review focuses on the mechanisms of plant-signal perception by MarR-like regulators, namely how they (i) allow bacteria to cope with the rhizosphere and plant endosphere, (ii) regulate the beneficial functions of Plant-Growth-Promoting Bacteria and (iii) regulate the virulence of phytopathogenic bacteria.

Insight into biodiversity of the recently rearranged genus Dickeya

The genus Dickeya includes plant pathogenic bacteria attacking a wide range of crops and ornamentals as well as a few environmental isolates from water. Defined on the basis of six species in 2005, this genus now includes 12 recognized species. Despite the description of several new species in recent years, the diversity of the genus Dickeya is not yet fully explored. Many strains have been analyzed for species causing diseases on economically important crops, such as for the potato pathogens D. dianthicola and D. solani. In contrast, only a few strains have been characterized for species of environmental origin or isolated from plants in understudied countries. To gain insights in the Dickeya diversity, recent extensive analyzes were performed on environmental isolates and poorly characterized strains from old collections. Phylogenetic and phenotypic analyzes led to the reclassification of D. paradisiaca (containing strains from tropical or subtropical regions) in the new genus, Musicola, the identification of three water species D. aquatica, D. lacustris and D. undicola, the description of a new species D. poaceaphila including Australian strains isolated from grasses, and the characterization of the new species D. oryzae and D. parazeae, resulting from the subdivision of the species D. zeae. Traits distinguishing each new species were identified from genomic and phenotypic comparisons. The high heterogeneity observed in some species, notably for D. zeae, indicates that additional species still need to be defined. The objective of this study was to clarify the present taxonomy of the genus Dickeya and to reassign the correct species to several Dickeya strains isolated before the current classification.

Putative pectate lyase PLL12 and callose deposition through polar CALS7 are necessary for long-distance phloem transport in Arabidopsis

In plants, the phloem distributes photosynthetic products for metabolism and storage over long distances. It relies on specialized cells, the sieve elements, which are enucleated and interconnected through large so-called sieve pores in their adjoining cell walls. Reverse genetics identified PECTATE LYASE-LIKE 12 (PLL12) as critical for plant growth and development. Using genetic complementations, we established that PLL12 is required exclusively late during sieve element differentiation. Structural homology modeling, enzyme inactivation, and overexpression suggest a vital role for PLL12 in sieve-element-specific pectin remodeling. While short distance symplastic diffusion is unaffected, the pll12 mutant is unable to accommodate sustained plant development due to an incapacity to accommodate increasing hydraulic demands on phloem long-distance transport as the plant grows-a defect that is aggravated when combined with another sieve-element-specific mutant callose synthase 7 (cals7). Establishing CALS7 as a specific sieve pore marker, we investigated the subcellular dynamics of callose deposition in the developing sieve plate. Using fluorescent CALS7 then allowed identifying structural defects in pll12 sieve pores that are moderate at the cellular level but become physiologically relevant due to the serial arrangement of sieve elements in the sieve tube. Overall, pectin degradation through PLL12 appears subtle in quantitative terms. We therefore speculate that PLL12 may act as a regulator to locally remove homogalacturonan, thus potentially enabling further extracellular enzymes to access and modify the cell wall during sieve pore maturation.

Effects of starters with different NDF/starch ratio on rumen fermentation parameters and rumen microorganisms in lambs

Starch and NDF are the main components in the diets of ruminants worldwide and are the main energy source for rumen microorganisms and hosts. The purpose of this study was to investigate the effects of different NDF/starch ratios on rumen fermentation parameters, rumen development and rumen microbes in lambs and to predict the function of rumen microbes by metagenomic techniques. In this study, 30 lambs with birth weights of (3.0 ± 0.5) kg were selected. The lambs of Hu sheep were randomly divided into two groups, fed starter with an NDF/starch ratio of 0.5 (group A) or 1.0 (group C). Samples of the rumen tissue and contents were collected after slaughter. The results showed that the ADG and ADFI of group A were significantly higher than those of group C (P < 0.05), but there was no significant difference in the FCR (P > 0.05). Therefore, from the perspective of feed-related economic benefits, group C showed greater economic value; the A/P of group C was significantly lower than that of group A (0.05 < P < 0.1), and the TVFA showed no significant difference (P > 0.05); The lengths of the rumen papillae of group C was significantly higher than that of group A (0.05 < P < 0.1). There was no significant difference in the abundance of the top 10 species at the phylum level and genus level (P > 0.05). CAZymes gene enrichment was observed in the rumen microbial community of lambs in group C (P < 0.05). In conclusion, group C, fed with starter with a higher NDF/starch ratio, had a higher feeding value. This study provides comprehensive insights into the composition of NDF and starch in lamb starter.

Two-component system ArcBA modulates cell motility and biofilm formation in Dickeya oryzae

Phytopathogen Dickeya oryzae is a causal agent of rice foot rot disease and the pathogen has an array of virulence factors, such as phytotoxin zeamines, plant cell wall degrading enzymes, cell motility, and biofilms, collectively contributing to the bacterial pathogenesis. In this study, through deletion analysis of predicted regulatory genes in D. oryzae EC1, we identified a two-component system associated with the regulation of bacterial virulence. The two-component system contains a histidine kinase ArcB and a response regulator ArcA, and deletion of their coding genes resulted in changed phenotypes in cell motility, biofilm formation, and bacterial virulence. Electrophoretic mobility shift assay revealed that ArcA bound to the promoters of the bcs operon and bssS, which respectively encode enzymes for the synthesis of celluloses and a biofilm formation regulatory protein. ArcA could also bind to the promoters of three virulence associated transcriptional regulatory genes, i.e., fis, slyA and ohrR. Surprisingly, although these three regulators were shown to modulate the production of cell wall degrading enzymes and zeamines, deletion of arcB and arcA did not seem to affect these phenotypes. Taken together, the findings from this study unveiled a new two-component system associated with the bacterial pathogenesis, which contributes to the virulence of D. oryzae mainly through its action on bacterial motility and biofilm formation.

Secondary structure and 1H, 15 N & 13C resonance assignments of the periplasmic domain of OutG, major pseudopilin from Dickeya dadantii type II secretion system

The ability to interact and adapt to the surrounding environment is vital for bacteria that colonise various niches and organisms. One strategy developed by Gram-negative bacteria is to secrete exoprotein substrates via the type II secretion system (T2SS). The T2SS is a proteinaceous complex spanning the bacterial envelope that translocates folded proteins such as toxins and enzymes from the periplasm to the extracellular milieu. In the T2SS, a cytoplasmic ATPase elongates in the periplasm the pseudopilus, a non-covalent polymer composed of protein subunits named pseudopilins, and anchored in the inner membrane by a transmembrane helix. The pseudopilus polymerisation is coupled to the secretion of substrates. The T2SS of Dickeya dadantii secretes more than 15 substrates, essentially plant cell wall degrading enzymes. In D. dadantii, the major pseudopilin or the major subunit of the pseudopilus is called OutG. To better understand the mechanism of secretion of these numerous substrates via the pseudopilus, we have been studying the structure of OutG by NMR. Here, as the first part of this study, we report the ¹H, ¹⁵N and ¹³C backbone and sidechain chemical shift assignment of the periplasmic domain of OutG and its NMR derived secondary structure.

Chemical and nutritional characteristics, and microbial degradation of rapeseed meal recalcitrant carbohydrates: A review

Approximately 35% of rapeseed meal (RSM) dry matter (DM) are carbohydrates, half of which are water-soluble carbohydrates. The cell wall of rapeseed meal contains arabinan, galactomannan, homogalacturonan, rhamnogalacturonan I, type II arabinogalactan, glucuronoxylan, XXGG-type and XXXG-type xyloglucan, and cellulose. Glycoside hydrolases including in the degradation of RSM carbohydrates are α-L-Arabinofuranosidases (EC 3.2.1.55), endo-α-1,5-L-arabinanases (EC 3.2.1.99), Endo-1,4-β-mannanase (EC 3.2.1.78), β-mannosidase (EC 3.2.1.25), α-galactosidase (EC 3.2.1.22), reducing-end-disaccharide-lyase (pectate disaccharide-lyase) (EC 4.2.2.9), (1 → 4)-6-O-methyl-α-D-galacturonan lyase (pectin lyase) (EC 4.2.2.10), (1 → 4)-α-D-galacturonan reducing-end-trisaccharide-lyase (pectate trisaccharide-lyase) (EC 4.2.2.22), α-1,4-D-galacturonan lyase (pectate lyase) (EC 4.2.2.2), (1 → 4)-α-D-galacturonan glycanohydrolase (endo-polygalacturonase) (EC 3.2.1.15), Rhamnogalacturonan hydrolase, Rhamnogalacturonan lyase (EC 4.2.2.23), Exo-β-1,3-galactanase (EC 3.2.1.145), endo-β-1,6-galactanase (EC 3.2.1.164), Endo-β-1,4-glucanase (EC 3.2.1.4), α-xylosidase (EC 3.2.1.177), β-glucosidase (EC 3.2.1.21) endo-β-1,4-glucanase (EC 3.2.1.4), exo-β-1,4-glucanase (EC 3.2.1.91), and β-glucosidase (EC 3.2.1.21). In conclusion, this review summarizes the chemical and nutritional compositions of RSM, and the microbial degradation of RSM cell wall carbohydrates which are important to allow to develop strategies to improve recalcitrant RSM carbohydrate degradation by the gut microbiota, and eventually to improve animal feed digestibility, feed efficiency, and animal performance.

Genetic Diversity of Pectobacterium spp. on Potato in Serbia

Pectobacterium is a diverse genus which comprises of multiple destructive bacterial species which cause soft rot/blackleg/wilt disease complex in a wide variety of crops by employing high levels of virulence factors. During the 2018, 2019 and 2020 potato growing seasons, numerous outbreaks of bacterial wilt, stem blackleg and tuber soft rot were recorded, and symptomatic plant samples from ten localities in the Province of Vojvodina (Serbia) were collected and analysed. Bacterial soft-rot pathogens were detected in 63 samples using genus and species-specific primers. Through 16S rRNA Sanger sequencing of 19 representative isolates, the identity of P. brasiliense (73.7%), P. punjabense (15.8%), and P. carotovorum (10.5%) species were revealed. To further validate the identification, genotypic profiling of Pectobacterium strains using rep-PCR (ERIC, BOX, REP) was conducted for 25 selected isolates and the phylogenetic assessment based on four selected housekeeping genes (gyrA, recA, rpoA, and rpoS). Physiological and biochemical properties were analysed using basic microbiological tests and VITEK^® 2 GN card, and pathogenicity was confirmed on cv. VR808 and cv. Desiree potato tubers and plants. This study confirmed the distinctiveness of the newly described P. punjabense in Serbia as well as the high diversity of Pectobacterium brasiliense and Pectobacterium carotovorum species in Serbia.

Biocontrol: Endophytic bacteria could be crucial to fight soft rot disease in the rare medicinal herb, Anoectochilus roxburghii

Microbial destabilization induced by pathogen infection has severely affected plant quality and output, such as Anoectochilus roxburghii, an economically important herb. Soft rot is the main disease that occurs during A. roxburghii culturing. However, the key members of pathogens and their interplay with non-detrimental microorganisms in diseased plants remain largely unsolved. Here, by utilizing a molecular ecological network approach, the interactions within bacterial communities in endophytic compartments and the surrounding soils during soft rot infection were investigated. Significant differences in bacterial diversity and community composition between healthy and diseased plants were observed, indicating that the endophytic communities were strongly influenced by pathogen invasion. Endophytic stem communities of the diseased plants were primarily derived from roots and the root endophytes were largely derived from rhizosphere soils, which depicts a possible pathogen migration image from soils to roots and finally the stems. Furthermore, interactions among microbial members indicated that pathogen invasion might be aided by positively correlated native microbial members, such as Enterobacter and Microbacterium, who may assist in colonization and multiplication through a mutualistic relationship in roots during the pathogen infection process. Our findings will help open new avenues for developing more accurate strategies for biological control of A. roxburghii bacterial soft rot disease.

Effect of a Stannous Fluoride Dentifrice on Biofilm Composition, Gene Expression and Biomechanical Properties

An in situ study was conducted to examine the mode of action of a 0.454% stannous fluoride (SnF₂)-containing dentifrice in controlling the composition and properties of oral biofilm. Thirteen generally healthy individuals participated in the study. Each participant wore an intra-oral appliance over a 48-h period to measure differences in the resulting biofilm’s architecture, mechanical properties, and bacterial composition after using two different toothpaste products. In addition, metatranscriptomics analysis of supragingival plaque was conducted to identify the gene pathways influenced. The thickness and volume of the microcolonies formed when brushing with the SnF₂ dentifrice were dramatically reduced compared to the control 0.76% sodium monofluorophosphate (MFP)-containing toothpaste. Similarly, the biophysical and nanomechanical properties measured by atomic force microscopy (AFM) demonstrated a significant reduction in biofilm adhesive properties. Metatranscriptomic analysis identified pathways associated with biofilm formation, cell adhesion, quorum sensing, and N-glycosylation that are significantly downregulated with SnF₂. This study provides a clinically relevant snapshot of how the use of a stabilized, SnF₂ toothpaste formulation can change the spatial organization, nanomechanical, and gene expression properties of bacterial communities.

The Diversity and Abundance of Soft Rot Pectobacteriaceae Along the Durance River Stream in the Southeast of France Revealed by Multiple Seasonal Surveys

Although irrigation water is frequently assessed for the presence of plant pathogens, large spatial and temporal surveys that provide clues on the diversity and circulation of pathogens are missing. We evaluate the diversity of soft rot Pectobacteriaceae (SRP) of the genera Dickeya and Pectobacterium over 2 years in a temperate, mixed-use watershed. The abundance of isolated strains correlates with the agricultural gradient along the watershed with a positive correlation found with temperature, nitrate, and dissolved organic carbon water concentration. We characterized 582 strains by amplification and sequencing of the gapA gene. Multilocus sequence analysis, performed with three housekeeping genes for 99 strains, and core genome analysis of 38 sequenced strains, confirmed for all the strains but one, the taxonomic assignation obtained with the sole gapA sequence. Pectobacterium spp. (549 isolates) were far more abundant than Dickeya spp. (33 isolates). Dickeya spp. were only observed in the lower part of the river when water temperature was >19°C, and we experimentally confirmed a decreased fitness of several Dickeya spp. at 8°C in river water. D. oryzae dominates the Dickeya spp. and P. versatile and P. aquaticum dominate the Pectobacterium spp., but their repartition along the watershed was different, with P. versatile being the only species regularly recovered all along the watershed. Excepting P. versatile, the Dickeya and Pectobacterium spp. responsible for disease outbreak on crops were less abundant or rarely detected. This work sheds light on the various ecological behaviors of different SRP types in stream water and indicates that SRP occupation is geographically structured.

Improvement on Thermostability of Pectate Lyase and Its Potential Application to Ramie Degumming

In order to obtain a thermostable pectate lyase for ramie degumming, a rational design based on structural analysis was carried out on a novel pectate lyase (Pel419) derived from the Dickeya Dadantii DCE-01 for high-efficiency ramie degumming. A total of five potential amino acid sites were chosen to replace residues. Then, the mutant enzymes were subjected to the heterologous expressions in Escherichia coli and their enzymatic characteristics were determined. The optimal reaction temperature for the five mutants kept consistent with that for the wild type. The enzyme activity and thermal stability of mutant V52A were significantly improved. Meanwhile, the weight loss rate obtained by V52A with the best enzymatic characteristics in the ramie degumming process at 50 °C is comparable with that obtained by commercial cotton-ramie processing pectinases, indicating that V52A was a potential industrial enzyme that could be applied to large-scale ramie degumming. In this study, the biological functions of conservative residues of Pel419 were preliminarily explored. The mutant V52A with both enzymatic activity and improved heat resistance was acquired, providing a superior material for developing enzyme preparations of ramie degumming, and rendering an effective method for the rational design aiming to improve the thermostability of pectate lyase.

Biochemical Characterization of a Pectate Lyase AnPL9 from Aspergillus nidulans

Pectinolytic enzymes have diverse industrial applications. Among these, pectate lyases act on the internal α-1,4-linkage of the pectate backbone, playing a critical role in pectin degradation. While most pectate lyases characterized thus far are of bacterial origin, fungi can also be excellent sources of pectinolytic enzymes. In this study, we performed biochemical characterization of the pectate lyase AnPL9 belonging to the polysaccharide lyase family 9 (PL9) from the filamentous fungus Aspergillus nidulans. Recombinant AnPL9 was produced using a Pichia pastoris expression system and purified. AnPL9 exhibited high activity on homogalacturonan (HG), pectin from citrus peel, pectin from apple, and the HG region in rhamnogalacturonan-I. Although digalacturonic acid and trigalacturonic acid were not degraded by AnPL9, tetragalacturonic acid was converted to 4,5-unsaturated digalacturonic acid and digalacturonic acid. These results indicate that AnPL9 degrades HG oligosaccharides with a degree of polymerization > 4. Furthermore, AnPL9 was stable within a neutral-to-alkaline pH range (pH 6.0-11.0). Our findings suggest that AnPL9 is a candidate pectate lyase for biotechnological applications in the food, paper, and textile industries. This is the first report on a fungal pectate lyase belonging to the PL9 family.

Scaffolding Protein GspB/OutB Facilitates Assembly of the Dickeya dadantii Type 2 Secretion System by Anchoring the Outer Membrane Secretin Pore to the Inner Membrane and to the Peptidoglycan Cell Wall

The phytopathogenic proteobacterium Dickeya dadantii secretes an array of plant cell wall-degrading enzymes and other virulence factors via the type 2 secretion system (T2SS). T2SSs are widespread among important plant, animal, and human bacterial pathogens. This multiprotein complex spans the double membrane cell envelope and secretes fully folded proteins through a large outer membrane pore formed by 15 subunits of the secretin GspD. Secretins are also found in the type 3 secretion system and the type 4 pili. Usually, specialized lipoproteins termed pilotins assist the targeting and assembly of secretins into the outer membrane. Here, we show that in D. dadantii, the pilotin acts in concert with the scaffolding protein GspB. Deletion of gspB profoundly impacts secretin assembly, pectinase secretion, and virulence. Structural studies reveal that GspB possesses a conserved periplasmic homology region domain that interacts directly with the N-terminal secretin domain. Site-specific photo-cross-linking unravels molecular details of the GspB-GspD complex in vivo. We show that GspB facilitates outer membrane targeting and assembly of the secretin pores and anchors them to the inner membrane while the C-terminal extension of GspB provides a scaffold for the secretin channel in the peptidoglycan cell wall. Phylogenetic analysis shows that in other bacteria, GspB homologs vary in length and domain composition and act in concert with either a cognate ATPase GspA or the pilotin GspS.

Biochemical characterization and immobilization of a novel pectate lyase ErPL2 for efficient preparation of pectin oligosaccharides

Pectate lyase (ErPL2) from Echinicola rosea JL3085 showed maximal activity at 45 °C and pH 9.0 with 0.6 mM CaCl₂. The K_m and V_max values of ErPL2 for polygalacturonic sodium were 2.098 mmol/L and 0.955 mmol/s, respectively. ErPL2 endolytically degraded pectic substances into oligosaccharides with degree of polymerization (DP) 1-5. To improve the thermostability and pH operation range, recombinant ErPL2 was immobilized onto mesoporous titanium oxide particles (MTOPs). MTOPs have abundant hydroxyl groups on the surface, which is a non-toxicity and good biocompatibility carrier. The residual enzyme activity of immobilized ErPL2 at 40 °C increased remarkably from 11% to 91% compared with free enzyme. The operable pH range was extended from 8-9 to 9-11. Surprisingly, the catalytic efficiency of immobilized ErPL2 was about 19 times higher than free enzyme. To our knowledge this is the first attempt of pectate lyase immobilized on MTOPs and it provides a new option for improving the catalytic performance.

Identification of new Dickeya dadantii virulence factors secreted by the type 2 secretion system

Dickeya are plant pathogenic bacteria able to provoke disease on a wide range of plants. A type 2 secretion system (T2SS) named Out is necessary for Dickeya virulence. Previous studies showed that the D. dadantii T2SS secretes a wide range of plant cell wall degrading enzymes, including pectinases and a cellulase. However, the full repertoire of exoproteins it can secrete has probably not yet been identified. Secreted proteins possess a signal peptide and are first addressed to the periplasm before their recruitment by Out. T2SS-specific secretion signals remain unknown which prevents in silico identification of T2SS substrates. To identify new Out substrates, we analyzed D. dadantii transcriptome data obtained in plant infection condition and searched for genes strongly induced and encoding proteins with a signal sequence. We identified four new Out-secreted proteins: the expansin YoaJ, the putative virulence factor VirK and two proteins of the DUF 4879 family, SvfA and SvfB. We showed that SvfA and SvfB are required for full virulence of D. dadantii and that svf genes are present in a variable number of copies in other Pectobacteriaceae, up to three in D. fanghzongdai. This work opens the way to the study of the role of non-pectinolytic proteins secreted by the Out pathway in Pectobacteriaceae.

Host range and virulence diversity of Pectobacterium carotovorum subsp. brasiliense strain RDKLR infecting radish in India, and development of a LAMP-based diagnostics

AIM

This work aimed at determining the pathogenicity, molecular characterization, host range and rapid detection of Pectobacterium carotovorum subsp. brasiliense (Pcb) causing soft rot disease in radish.

METHOD AND RESULTS

The four isolated isolates were inoculated to radish, typical soft rot symptoms were observed and Koch's postulates were proved. The most virulent strain RDKLR was morphologically and biochemically distinct. Pcb showed a positive potato soft rot test and elicited hypersensitivity response on Nicotiana tobaccum. The genes Pel2 and pmrA were used for sub-species characterization of Pcb. It has a wide host range and infection was observed on slices of carrot, tomato, cauliflower, cabbage, chili, knol-khol, bell pepper and cucumber. Infectivity was also seen in seedlings under glasshouse conditions. Pcb produced cell wall degrading enzymes in semi-quantification assay and is a strong biofilm producer. The LAMP technique was standardized to help rapid detection and take prophylactic measures to manage the disease.

CONCLUSION

This work reports Pcb as a new soft rot causing organism of radish in India. Pcb is highly virulent with a broad host range. The LAMP technique helps in rapid detection.

SIGNIFICANCE AND IMPACT OF STUDY

Pcb-induced soft rot causes significant yield loss, decreased market value, damage in transit, storage, and the market. Disease characterisation and early identification aid in disease management and prevention in the field.

Evaluation of Extended-Release of Piroxicam Loaded Pectin-Zein Hydrogel Microspheres: In Vitro, Ex Vivo, and In Vivo Studies

OBJECTIVE

This study evaluated drug delivery systems based on Pectin (P) and Zein (Z) hydrogel microspheres. Piroxicam (Px) loaded P/Z hydrogel microspheres (P/Z HM) were developed, and their extended-release pharmacokinetic properties were evaluated.

METHODS

Experiments were executed under three different conditions: in vitro, ex vivo, and in vivo. Then, the in vitro-in vivo correlations (IVIVC) and ex vivo - in vivo correlations (EVIVC) were examined.

RESULTS

Analysis of drug release mechanisms were evaluated by fitting the in vitro data into the Ritger-Peppas equation, showing the contribution of both polymers' relaxation and drug diffusion from the hydrogel microspheres. The fraction absorbed in vivo was determined by the deconvolution of plasma concentration data using the Loo-Riegelman method. After oral single-dose administration of the two formulations, their basic independent model parameters were calculated.

CONCLUSION

P/Z HM had different drug release behaviors in in vitro and in vivo conditions. However, the ex vivo and in vivo characteristics were similar (R² = 0.99). This seemed reasonable to use the ex vivo method to predict the in vivo drug absorption behavior during the polymeric drug delivery system developmental studies. The P/Z HM formulation maintained the drug dose at the colon site for a long duration and could be applied for delivery of active pharmaceutical and food ingredients to the colon site.

Response of Coastal Shewanella and Duganella Bacteria to Planktonic and Terrestrial Food Substrates

Global warming scenarios indicate that in subarctic regions, the precipitation will increase in the future. Coastal bacteria will thus receive increasing organic carbon sources from land runoff. How such changes will affect the function and taxonomic composition of coastal bacteria is poorly known. We performed a 10-day experiment with two isolated bacteria: Shewanella baltica from a seaside location and Duganella sp. from a river mouth, and provided them with a plankton and a river extract as food substrate. The bacterial growth and carbon consumption were monitored over the experimental period. Shewanella and Duganella consumed 40% and 30% of the plankton extract, respectively, while the consumption of the river extract was low for both bacteria, ∼1%. Shewanella showed the highest bacterial growth efficiency (BGE) (12%) when grown on plankton extract, while when grown on river extract, the BGE was only 1%. Duganella showed low BGE when grown on plankton extract (< 1%) and slightly higher BGE when grown on river extract (2%). The cell growth yield of Duganella was higher than that of Shewanella when grown on river extract. These results indicate that Duganella is more adapted to terrestrial organic substrates with low nutritional availability, while Shewanella is adapted to eutrophied conditions. The different growth performance of the bacteria could be traced to genomic variations. A closely related genome of Shewanella was shown to harbor genes for the sequestration of autochthonously produced carbon substrates, while Duganella contained genes for the degradation of relatively refractive terrestrial organic matter. The results may reflect the influence of environmental drivers on bacterial community composition in natural aquatic environments. Elevated inflows of terrestrial organic matter to coastal areas in subarctic regions would lead to increased occurrence of bacteria adapted to the degradation of complex terrestrial compounds with a low bioavailability.

Genomic Comparisons and Phenotypic Diversity of Dickeya zeae Strains Causing Bacterial Soft Rot of Banana in China

Bacterial soft rot of banana, caused by Dickeya zeae, is spreading rapidly in important banana growing areas in China and seriously threatens banana production. In this study, we sequenced the high-quality complete genomes of three typical banana strains, MS1 (size: 4,831,702-bp; genome coverages: 538x), MS_2014 (size: 4,740,000-bp; genome coverages: 586x) and MS_2018 (size: 4,787,201-bp; genome coverages: 583x), isolated in 2009, 2014, and 2018, respectively. To determine their genomic and phenotypic diversity with respect to their hosts of origin, they were compared with other D. zeae strains, including another representative banana strain MS2 from China. The sequenced strains were similar in utilization of carbon source and chemical substrates, and general genomic features of GC content, and tRNA and rRNA regions. They were also conserved in most virulence determinants, including gene-encoding secretion systems, plant cell wall degrading enzymes, and exopolysaccharides. We further explored their genomic diversity in the predicted genomic islands (GIs). These GIs were rich in integrases and transposases, where some genomic dissimilarity was observed in the flagellar gene cluster and several secondary metabolite gene clusters. Different constituents of core biosynthetic modules were found within the bacteriocin and aryl polyene (APE) pigment gene clusters, and the strains from banana showed different phenotypes with respect to antibiosis effects and colony pigmentation. Additionally, clustered regularly interspaced short palindromic repeat (CRISPR) and prophage elements, such as type I-F and III-A CRISPR arrays and an intact prophage of MS1-P5, contributed to bacterial diversity. Phylogenetic tree analysis and genome-genome nucleotide comparison confirmed the genomic divergence among the strains isolated from banana. Considering these characteristics, MS2 and MS_2014 probably diverged later than MS1, while MS_2018 was different and more similar to foreign strains isolated from other hosts in several characteristics. Strain MS_2018 caused severe symptoms on banana varieties previously considered moderately resistant or moderately susceptible, including varieties of Cavendish (Musa AAA) and Plantain (Musa ABB). Our study of genomic and phenotypic diversity raises public attention to the risk of spreading new pathogenic variants within banana growing regions and supports development of predictive strategies for disease control.

Dickeya Manipulates Multiple Quorum Sensing Systems to Control Virulence and Collective Behaviors

Soft rot Pectobacteriaceae (SRP), typical of Pectobacterium and Dickeya, are a class of Gram-negative bacterial pathogens that cause devastating diseases on a wide range of crops and ornamental plants worldwide. Quorum sensing (QS) is a cell-cell communication mechanism regulating the expression of specific genes by releasing QS signal molecules associated with cell density, in most cases, involving in the vital process of virulence and infection. In recent years, several types of QS systems have been uncovered in Dickeya pathogens to control diverse biological behaviors, especially bacterial pathogenicity and transkingdom interactions. This review depicts an integral QS regulation network of Dickeya, elaborates in detail the regulation of specific QS system on different biological functions of the pathogens and hosts, aiming at providing a systematic overview of Dickeya pathogenicity and interactions with hosts, and, finally, expects the future prospective of effectively controlling the bacterial soft rot disease caused by Dickeya by quenching the key QS signal.

Biocontrol Activity of Aspergillus terreus ANU-301 against Two Distinct Plant Diseases, Tomato Fusarium Wilt and Potato Soft Rot

To screen antagonistic fungi against plant pathogens, dual culture assay (DCA) and culture filtrate assay (CFA) were performed with unknown soil-born fungi. Among the different fungi isolated and screened from the soil, fungal isolate ANU-301 successfully inhibited growth of different plant pathogenic fungi, Colletotrichum acutatum, Alternaria alternata, and Fusarium oxysporum, in DCA and CFA. Morphological characteristics and rDNA internal transcribed spacer sequence analysis identified ANU-301 as Aspergillus terreus. Inoculation of tomato plants with Fusarium oxysporum f. sp. lycopersici (FOL) induced severe wilting symptom; however, co-inoculation with ANU-301 significantly enhanced resistance of tomato plants against FOL. In addition, culture filtrate (CF) of ANU-301 not only showed bacterial growth inhibition activity against Dickeya chrysanthemi (Dc), but also demonstrated protective effect in potato tuber against soft rot disease. Gas chromatography-tandem mass spectrometry analysis of CF of ANU-301 identified 2,4-bis(1-methyl-1-phenylethyl)-phenol (MPP) as the most abundant compound. MPP inhibited growth of Dc, but not of FOL, in a dose-dependent manner, and protected potato tuber from the soft rot disease induced by Dc. In conclusion, Aspergillus terreus ANU-301 could be used and further tested as a potential biological control agent.

Specificity and genetic polymorphism in the Vfm quorum sensing system of plant pathogenic bacteria of the genus Dickeya

The Vfm quorum sensing (QS) system is preponderant for the virulence of different species of the bacterial genus Dickeya. The vfm gene cluster encodes 26 genes involved in the production, sensing or transduction of the QS signal. To date, the Vfm QS signal has escaped detection by analytical chemistry methods. However, we report here a strain‐specific polymorphism in the biosynthesis genes vfmO and vfmP, which is predicted to be related to the production of different analogues of the QS signal. Consequently, the Vfm communication could be impossible between strains possessing different variants of the genes vfmO/P. We constructed three Vfm QS biosensor strains possessing different vfmO/P variants and compared these biosensors for their responses to samples prepared from 34 Dickeya strains possessing different vfmO/P variants. A pattern of specificity was demonstrated, providing evidence that the polymorphism in the genes vfmO/P determines the biosynthesis of different analogues of the QS signal. Unexpectedly, this vfmO/P‐dependent pattern of specificity is linked to a polymorphism in the ABC transporter gene vfmG, suggesting an adaptation of the putative permease VfmG to specifically bind different analogues of the QS signal. Accordingly, we discuss the possible involvement of VfmG as co‐sensor of the Vfm two‐component regulatory system.

The Periplasmic Oxidoreductase DsbA Is Required for Virulence of the Phytopathogen Dickeya solani

In bacteria, the DsbA oxidoreductase is a crucial factor responsible for the introduction of disulfide bonds to extracytoplasmic proteins, which include important virulence factors. A lack of proper disulfide bonds frequently leads to instability and/or loss of protein function; therefore, improper disulfide bonding may lead to avirulent phenotypes. The importance of the DsbA function in phytopathogens has not been extensively studied yet. Dickeya solani is a bacterium from the Soft Rot Pectobacteriaceae family which is responsible for very high economic losses mainly in potato. In this work, we constructed a D. solani dsbA mutant and demonstrated that a lack of DsbA caused a loss of virulence. The mutant bacteria showed lower activities of secreted virulence determinants and were unable to develop disease symptoms in a potato plant. The SWATH-MS-based proteomic analysis revealed that the dsbA mutation led to multifaceted effects in the D. solani cells, including not only lower levels of secreted virulence factors, but also the induction of stress responses. Finally, the outer membrane barrier seemed to be disturbed by the mutation. Our results clearly demonstrate that the function played by the DsbA oxidoreductase is crucial for D. solani virulence, and a lack of DsbA significantly disturbs cellular physiology.

OhrR is a central transcriptional regulator of virulence in Dickeya zeae

Dickeya zeae is the causal agent of rice foot rot disease. The pathogen is known to rely on a range of virulence factors, including phytotoxin zeamines, extracellular enzymes, cell motility, and biofilm, which collectively contribute to the establishment of infections. Phytotoxin zeamines play a critical role in bacterial virulence; signalling pathways and regulatory mechanisms that govern bacterial virulence remain unclear. In this study, we identified a transcriptional regulator OhrR (organic hydroperoxide reductase regulator) that is involved in the regulation of zeamine production in D. zeae EC1. The OhrR null mutant was significantly attenuated in its virulence against rice seed, potato tubers and radish roots. Phenotype analysis showed that OhrR was also involved in the regulation of other virulence traits, including the production of extracellular cellulase, biofilm formation, and swimming/swarming motility. DNA electrophoretic mobility shift assay showed that OhrR directly regulates the transcription of key virulence genes and genes encoding bis-(3'-5')-cyclic dimeric guanosine monophosphate synthetases. Furthermore, OhrR positively regulates the transcription of regulatory genes slyA and fis through binding to their promoter regions. Our findings identify a key regulator of the virulence of D. zeae and add new insights into the complex regulatory network that modulates the physiology and virulence of D. zeae.

Standard Candles for Dating Microbial Lineages

Molecular clock analyses are challenging for microbial phylogenies, due to a lack of fossil calibrations that can reliably provide absolute time constraints. An alternative source of temporal constraints for microbial groups is provided by the inheritance of proteins that are specific for the utilization of eukaryote-derived substrates, which have often been dispersed across the Tree of Life via horizontal gene transfer. In particular, animal, algal, and plant-derived substrates are often produced by groups with more precisely known divergence times, providing an older-bound on their availability within microbial environments. Therefore, these ages can serve as "standard candles" for dating microbial groups across the Tree of Life, expanding the reach of informative molecular clock investigations. Here, we formally develop the concept of substrate standard candles and describe how they can be propagated and applied using both microbial species trees and individual gene family phylogenies. We also provide detailed evaluations of several candidate standard candles and discuss their suitability in light of their often complex evolutionary and metabolic histories.

Improving the Thermo-Activity and -Stability of Pectate Lyase from Dickeya dadantii DCE-01 for Ramie Degumming

To improve the thermal stability of pectate lyase for ramie degumming, we modified the novel pectate lyase gene (pelG403) derived from the Dickeya dadantii DCE-01 high-efficiency ramie degumming strain by site-directed mutagenesis. Twelve mutants were acquired, wherein a prospective mutant (A129V) showed better enzyme activity and thermal stability. Compared with the wild type (PelG403), the specific enzyme activity and the optimal reaction temperature of A129V in the fermentation broth increased by 20.1%, and 5 °C, respectively. Under the conditions of 55 °C and pH 9.0, the weightlessness rate of ramie raw materials of A129V increased by 6.26%. Therefore, this study successfully improved the enzyme activity and heat resistance of PelG403 in an alkaline environment, which may contribute to the development of enzyme preparations and the elucidation of the mechanism for ramie bio-degumming.

Membrane Vesicles of Pectobacterium as an Effective Protein Secretion System

Bacteria of genus Pectobacterium are Gram-negative rods of the family Pectobacteriaceae. They are the causative agent of soft rot diseases of crops and ornamental plants. However, their virulence mechanisms are not yet fully elucidated. Membrane vesicles (MVs) are universally released by bacteria and are believed to play an important role in the pathogenicity and survival of bacteria in the environment. Our study investigates the role of MVs in the virulence of Pectobacterium. The results indicate that the morphology and MVs production depend on growth medium composition. In polygalacturonic acid (PGA) supplemented media, Pectobacterium produces large MVs (100–300 nm) and small vesicles below 100 nm. Proteomic analyses revealed the presence of pectate degrading enzymes in the MVs. The pectate plate test and enzymatic assay proved that those enzymes are active and able to degrade pectates. What is more, the pathogenicity test indicated that the MVs derived from Pectobacterium were able to induce maceration of Zantedeschia sp. leaves. We also show that the MVs of β-lactamase producing strains were able to suppress ampicillin activity and permit the growth of susceptible bacteria. Those findings indicate that the MVs of Pectobacterium play an important role in host-pathogen interactions and niche competition with other bacteria. Our research also sheds some light on the mechanism of MVs production. We demonstrate that the MVs production in Pectobacterium strains, which overexpress a green fluorescence protein (GFP), is higher than in wild-type strains. Moreover, proteomic analysis revealed that the GFP was present in the MVs. Therefore, it is possible that protein sequestration into MVs might not be strictly limited to periplasmic proteins. Our research highlights the importance of MVs production as a mechanism of cargo delivery in Pectobacterium and an effective secretion system.

Proposal for the creation of a new genus Musicola gen. nov., reclassification of Dickeya paradisiaca (Samson et al. 2005) as Musicola paradisiaca comb. nov. and description of a new species Musicola keenii sp. nov

The Pectobacteriaceae family of important plant pathogens includes the genus Dickeya. There are currently 12 described species of Dickeya, although some are poorly characterized at the genomic level. Only two genomes of Dickeya paradisiaca, the type strain CFBP 4178^T and strain Ech703, have previously been sequenced. Members of this species are mostly of tropical or subtropical origin. During an investigation of strains present in our laboratory collection we sequenced the atypical strain A3967, registered as CFBP 722, isolated from Solanum lycopersicum (tomato) in the South of France in 1965. The genome of strain A3967 shares digital DNA-DNA hybridization and average nucleotide identity (ANI) values of 68 and 96 %, respectively, with the D. paradisiaca type strain CFBP 4178^T. However, ANI analysis showed that D. paradisiaca strains are significantly dissimilar to the other Dickeya species, such that less than one third of their genomes align to any other Dickeya genome. On phenotypic, phylogenetic and genomic grounds, we propose a reassignment of D. paradisiaca to the genus level, for which we propose the name Musicola gen. nov., with Musicola paradisiaca as the type species and CFBP 4178^T (NCPPB 2511^T) as the type strain. Phenotypic analysis showed differences between strain A3967^T and CFBP 4178^T, such as for the assimilation of melibiose, raffinose and myo-inositol. These results support the description of two novel species, namely Musicola paradisiaca comb. nov. and Musicola keenii sp. nov., with CFBP 4178^T (NCPPB 2511^T=LMG 2542^T) and A3967^T (CFBP 8732^T=LMG 31880^T) as the type strains, respectively.

Identification of Pectobacterium versatile Causing Blackleg of Potato in New York State

Soft rot bacteria classified in the Pectobacteriaceae (SRP), including Pectobacterium and Dickeya spp., are responsible for soft rot and blackleg diseases of potato. Since 2014, blackleg outbreaks caused by D. dianthicola have increased in the United States and Canada. Our previous study found that the most abundant causal organisms of blackleg disease in New York State were P. parmentieri and D. dianthicola, with the latter being the only Dickeya species reported. In the present study, we identified and characterized pathogenic SRP bacteria from 19 potato samples collected in New York State during the 2017 growing season. We used genome sequence comparison to determine the pathogens' species. We found eight P. versatile, one P. atrosepticum, two P. carotovorum, two P. parmentieri, and six D. dianthicola isolates in our 2017 SRP collection. This is the first time that P. versatile has been reported to cause potato blackleg disease in New York State. We determined the phylogenetic relationships between the SRP strains by using 151 single-copy orthologous gene sequences shared among the set of bacteria in our analysis, which provided better resolution than phylogenies constructed with the dnaX gene.

Exploration of the Quorum-Quenching Mechanism in Pseudomonas nitroreducens W-7 and Its Potential to Attenuate the Virulence of Dickeya zeae EC1

Quorum quenching (QQ) is a novel, promising strategy that opens up a new perspective for controlling quorum-sensing (QS)-mediated bacterial pathogens. QQ is performed by interfering with population-sensing systems, such as by the inhibition of signal synthesis, catalysis of degrading enzymes, and modification of signals. In many Gram-negative pathogenic bacteria, a class of chemically conserved signaling molecules named N-acyl homoserine lactones (AHLs) have been widely studied. AHLs are involved in the modulation of virulence factors in various bacterial pathogens including Dickeya zeae. Dickeya zeae is the causal agent of plant-rot disease of bananas, rice, maize, potatoes, etc., causing enormous economic losses of crops. In this study, a highly efficient AHL-degrading bacterial strain W-7 was isolated from activated-sludge samples and identified as Pseudomonas nitroreducens. Strain W-7 revealed a superior ability to degrade N-(3-oxododecanoyl)-l-homoserine lactone (OdDHL) and completely degraded 0.2 mmol/L of OdDHL within 48 h. Gas chromatography-mass spectrometry (GC-MS) identified N-cyclohexyl-propanamide as the main intermediate metabolite during AHL biodegradation. A metabolic pathway for AHL in strain W-7 was proposed based on the chemical structure of AHL and intermediate products. In addition to the degradation of OdDHL, this strain was also found to be capable of degrading a wide range of AHLs including N-(3-oxohexanoyl)-l-homoserine lactone (OHHL), N-(3-oxooctanoyl)-l-homoserine lactone (OOHL), and N-hexanoyl-l-homoserine lactone (HHL). Moreover, the application of strain W-7 as a biocontrol agent could substantially attenuate the soft rot caused by D. zeae EC1 to suppress tissue maceration in various host plants. Similarly, the application of crude enzymes of strain W-7 significantly reduced the disease incidence and severity in host plants. These original findings unveil the biochemical aspects of a highly efficient AHL-degrading bacterial isolate and provide useful agents that exhibit great potential for the control of infectious diseases caused by AHL-dependent bacterial pathogens.

Genomic and Phenotypic Biology of Novel Strains of Dickeya zeae Isolated From Pineapple and Taro in Hawaii: Insights Into Genome Plasticity, Pathogenicity, and Virulence Determinants

Dickeya zeae, a bacterial plant pathogen of the family Pectobacteriaceae, is responsible for a wide range of diseases on potato, maize, rice, banana, pineapple, taro, and ornamentals and significantly reduces crop production. D. zeae causes the soft rot of taro (Colocasia esculenta) and the heart rot of pineapple (Ananas comosus). In this study, we used Pacific Biosciences single-molecule real-time (SMRT) sequencing to sequence two high-quality complete genomes of novel strains of D. zeae: PL65 (size: 4.74997 MB; depth: 701x; GC: 53.6%) and A5410 (size: 4.7792 MB; depth: 558x; GC: 53.5%) isolated from economically important Hawaiian crops, taro, and pineapple, respectively. Additional complete genomes of D. zeae representing three additional hosts (philodendron, rice, and banana) and other species used for a taxonomic comparison were retrieved from the NCBI GenBank genome database. Genomic analyses indicated the truncated type III and IV secretion systems (T3SS and T4SS) in the taro strain, which only harbored one and two genes of T3SS and T4SS, respectively, and showed high heterogeneity in the type VI secretion system (T6SS). Unlike strain EC1, which was isolated from rice and recently reclassified as D. oryzae, neither the genome PL65 nor A5410 harbors the zeamine biosynthesis gene cluster, which plays a key role in virulence of other Dickeya species. The percentages of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) between the two genomes were 94.47 and 57.00, respectively. In this study, we compared the major virulence factors [plant cell wall-degrading extracellular enzymes and protease (Prt)] produced by D. zeae strains and evaluated the virulence on taro corms and pineapple leaves. Both strains produced Prts, pectate lyases (Pels), and cellulases but no significant quantitative differences were observed (p > 0.05) between the strains. All the strains produced symptoms on taro corms and pineapple leaves, but the strain PL65 produced symptoms more rapidly than others. Our study highlights the genetic constituents of pathogenicity determinants and genomic heterogeneity that will help to understand the virulence mechanisms and aggressiveness of this plant pathogen.