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.

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.

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.

A natural single nucleotide mutation in the small regulatory RNA ArcZ of Dickeya solani switches off the antimicrobial activities against yeast and bacteria.

The necrotrophic plant pathogenic bacterium Dickeya solani emerged in the potato agrosystem in Europe. All isolated strains of D. solani contain several large polyketide synthase/non-ribosomal peptide synthetase (PKS/NRPS) gene clusters. Analogy with genes described in other bacteria suggests that the clusters ooc and zms are involved in the production of secondary metabolites of the oocydin and zeamine families, respectively. A third cluster named sol was recently shown to produce an antifungal molecule. In this study, we constructed mutants impaired in each of the three secondary metabolite clusters sol, ooc, and zms to compare first the phenotype of the D. solani wild-type strain D s0432-1 with its associated mutants. We demonstrated the antimicrobial functions of these three PKS/NRPS clusters against bacteria, yeasts or fungi. The cluster sol, conserved in several other Dickeya species, produces a secondary metabolite inhibiting yeasts. Phenotyping and comparative genomics of different D. solani wild-type isolates revealed that the small regulatory RNA ArcZ plays a major role in the control of the clusters sol and zms. A single-point mutation, conserved in some Dickeya wild-type strains, including the D. solani type strain IPO 2222, impairs the ArcZ function by affecting its processing into an active form.

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.

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.

Diversity within the Dickeya zeae complex, identification of Dickeya zeae and Dickeya oryzae members, proposal of the novel species Dickeya parazeae sp. nov.

The genus Dickeya comprises plant pathogens that cause diseases in a large range of economically important crops and ornamentals. Strains previously assigned to the species Dickeya zeae are major pathogens attacking vital crops such as maize and rice. They are also frequently isolated from surface water. The newly described species Dickeya oryzae is closely related to D. zeae members, so that the limit between the two species can be difficult to define. In order to clearly distinguish the two species, globally described by the term 'D. zeae complex', we sequenced the genome of four new water isolates and compared them to 14 genomes available in databases. Calculation of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values confirmed the phylogenomic classification into the two species D. zeae and D. oryzae. It also allowed us to propose a new species, Dickeya parazeae sp. nov., to characterize a clade distinct from those containing the D. zeae type strain NCPPB2538T. Strain S31T (CFBP 8716T=LMG 32070T) isolated from water in France is proposed as the type strain of the new species. Phenotypic analysis of eight publically available strains revealed traits common to the five tested D. oryzae members but apparently not shared by the D. oryzae type strain. Genomic analyses indicated that a simple distinction between the species D. zeae, D. parazeae and D. oryzae can be obtained on the basis of the recA sequence. D. oryzae can be distinguished from the two other species by growth on l-tartaric acid. Based on the recA marker, several strains previously identified as D. zeae were re-assigned to the species D. parazeae or D. oryzae. This study also highlighted the broad host range diversity of these three species.

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 4178T 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 4178T. 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 4178T (NCPPB 2511T) as the type strain. Phenotypic analysis showed differences between strain A3967T and CFBP 4178T, 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 4178T (NCPPB 2511T=LMG 2542T) and A3967T (CFBP 8732T=LMG 31880T) as the type strains, respectively.

Genome-Wide Identification of Dickeya solani Transcriptional Units Up-Regulated in Response to Plant Tissues From a Crop-Host Solanum tuberosum and a Weed-Host Solanum dulcamara.

Dickeya solani is a Gram-negative bacterium able to cause disease symptoms on a variety of crop and ornamental plants worldwide. Weeds including Solanum dulcamara (bittersweet nightshade) growing near agricultural fields have been reported to support populations of soft rot bacteria in natural settings. However, little is known about the specific interaction of D. solani with such weed plants that may contribute to its success as an agricultural pathogen. The aim of this work was to assess the interaction of D. solani with its crop plant (Solanum tuberosum) and an alternative (S. dulcamara) host plant. From a collection of 10,000 Tn5 transposon mutants of D. solani IPO2222 carrying an inducible, promotorless gusA reporter gene, 210 were identified that exhibited plant tissue-dependent expression of the gene/operon into which the Tn5 insertion had occurred. Thirteen Tn5 mutants exhibiting the greatest plant tissue induction of such transcriptional units in S. tuberosum or S. dulcamara as measured by qRT-PCR were assessed for plant host colonization, virulence, and ability to macerate plant tissue, as well as phenotypes likely to contribute to the ecological fitness of D. solani, including growth rate, carbon and nitrogen source utilization, motility, chemotaxis toward plant extracts, biofilm formation, growth under anaerobic conditions and quorum sensing. These 13 transcriptional units encode proteins involved in bacterial interactions with plants, with functions linked to cell envelope structure, chemotaxis and carbon metabolism. The selected 13 genes/operons were differentially expressed in, and thus contributed preferentially to D. solani fitness in potato and/or S. dulcamara stem, leaf, and root tissues.

Dickeya poaceiphila sp. nov., a plant-pathogenic bacterium isolated from sugar cane (Saccharum officinarum).

The genus Dickeya is an important group of plant pathogens that currently comprises 10 recognized species. Although most Dickeya isolates originated from infected cultivated plants, they are also isolated from water. The genomic sequence of the Australian strain NCPPB 569T clearly established its separation from the previously characterized Dickeya species. The average nucleotide identity and digital DNA-DNA hybridization values obtained by comparing strain NCPPB 569T with strains of characterized Dickeya species were lower than 87 and 32 %, respectively, supporting the delineation of a new species. The name Dickeya poaceiphila sp. nov. is proposed for this taxon with the type strain NCPPB 569T (=CFBP 8731T). Two other strains isolated in Australia, CFBP 1537 and CFBP 2040, also belong to this species. Phenotypic and genomic comparisons enabled the identification of traits distinguishing D. poaceiphila isolates from strains of other Dickeya species.

The metabolic shift in highly and weakly virulent Dickeya solani strains is more affected by temperature than by mutations in genes encoding global virulence regulators.

Global warming may shortly increase the risk of disease development on plants. Significant differences in the metabolic activity screened with Phenotype Microarray at 22°C and 28°C were observed between D. solani strains with high and low virulence level. Highly virulent D. solani was characterized by a higher number of metabolized compounds and a faster metabolism and was more tolerant to non-favorable pH and osmolarity. Metabolic phenotyping showed for the first time that the mutation in pecT gene, which encodes a global repressor of virulence, affects several pathways of the basic cell metabolism. PecT mutants had a higher maceration capacity of potato tissue and showed a higher pectinolytic activity than the wild-type strains. On the contrary, mutation in expI gene, which encoded the signaling molecules synthase crucial for quorum sensing, had an insignificant effect on the cell metabolism, although it slightly reduced the potato tissue maceration. The ability to utilize most of the tested compounds was higher at 28°C, while the survival at non-favorable pH and osmolarity was higher at 22°C. These results proved that the temperature of incubation had the most significant impact on the D. solani metabolic profiles.

Genomic characterization of a pectinolytic isolate of Serratia oryzae isolated from lake water.

Only one isolate of Serratia oryzae, the type strain J11-6T has been characterized up to now. This strain was found in the endophytic bacterial flora of rice. As part of an ongoing investigation into pectinolytic bacteria present in lake water in France, a few Serratia strains were isolated, including S32 and J9 identified as new strains of S. oryzae. The genome of strain S32 consists of a circular chromosome of 4,810,389 bp that contains 4,584 protein-coding genes. The genome of S32, as well as those of the type strain J11-6T, contains several genes involved in pectin degradation and in the intracellular assimilation of pectin oligomers. The specific detection of enzyme activities confirmed that strain S32 secretes functional pectinases and that it also produces extracellular cellulase and protease activities. The ability to produce plant cell wall degrading enzymes shows that S. oryzae shares characteristics of plant associated bacteria, including phytopathogens.

Dickeya lacustris sp. nov., a water-living pectinolytic bacterium isolated from lakes in France.

The genus Dickeya is an important group of plant pathogens that currently comprises eight recognized species. Although most Dickeya isolates originated from infected cultivated plants, they have also been repeatedly isolated from water. To better understand the natural diversity of Dickeya, a survey was performed in small lakes surrounded by wetlands in the French region of La Dombes. Several Dickeya isolates were obtained from water or plants from lakes protected from direct agricultural inputs. Sequencing of the gapA gene revealed that five isolates, S12, S15, S24, S29T and S39, belong to a phylogenetic group separated from other Dickeya species. The genomic sequence of strain S29T clearly established its separation from the other known Dickeya species. The in silico DNA-DNA hybridization (isDDH) and average nucleotide identity (ANI) values (<33 and <88 %, respectively) obtained by comparing strain S29T with strains of characterized Dickeya species supported the delineation of a novel species. The closest species to strain S29T is Dickeya aquatica, previously isolated from rivers, suggesting that these strains have a common ancestor adapted to a water environment. Genomic and phenotypic comparisons enabled the identification of traits distinguishing isolates S12, S15, S24, S29T and S39 from D. aquatica and from other Dickeya species. The name Dickeya lacustris sp. nov. is proposed for this taxon with S29T (=CFBP 8647T=LMG 30899T) as the type strain.

Comparison of Highly and Weakly Virulent Dickeya solani Strains, With a View on the Pangenome and Panregulon of This Species.

Bacteria belonging to the genera Dickeya and Pectobacterium are responsible for significant economic losses in a wide variety of crops and ornamentals. During last years, increasing losses in potato production have been attributed to the appearance of Dickeya solani. The D. solani strains investigated so far share genetic homogeneity, although different virulence levels were observed among strains of various origins. The purpose of this study was to investigate the genetic traits possibly related to the diverse virulence levels by means of comparative genomics. First, we developed a new genome assembly pipeline which allowed us to complete the D. solani genomes. Four de novo sequenced and ten publicly available genomes were used to identify the structure of the D. solani pangenome, in which 74.8 and 25.2% of genes were grouped into the core and dispensable genome, respectively. For D. solani panregulon analysis, we performed a binding site prediction for four transcription factors, namely CRP, KdgR, PecS and Fur, to detect the regulons of these virulence regulators. Most of the D. solani potential virulence factors were predicted to belong to the accessory regulons of CRP, KdgR, and PecS. Thus, some differences in gene expression could exist between D. solani strains. The comparison between a highly and a low virulent strain, IFB0099 and IFB0223, respectively, disclosed only small differences between their genomes but significant differences in the production of virulence factors like pectinases, cellulases and proteases, and in their mobility. The D. solani strains also diverge in the number and size of prophages present in their genomes. Another relevant difference is the disruption of the adhesin gene fhaB2 in the highly virulent strain. Strain IFB0223, which has a complete adhesin gene, is less mobile and less aggressive than IFB0099. This suggests that in this case, mobility rather than adherence is needed in order to trigger disease symptoms. This study highlights the utility of comparative genomics in predicting D. solani traits involved in the aggressiveness of this emerging plant pathogen.

Interplay of classic Exp and specific Vfm quorum sensing systems on the phenotypic features of Dickeya solani strains exhibiting different virulence levels.

Bacteria from the genus Dickeya cause severe symptoms on numerous economically important plants. Dickeya solani is the Dickeya species most frequently found on infected potato plants in Europe. D. solani strains from different countries show high genetic homogeneity, but significant differences in their virulence level. Dickeya species possess two quorum sensing (QS) mechanisms: the Exp system based on classic N-acyl-homoserine lactone (AHL) signals and a specific system depending on the production and perception of a molecule of unknown structure, Virulence Factor Modulating (VFM). To study the interplay between these two QS systems, five D. solani strains exhibiting different virulence levels were selected. Mutants were constructed by inactivating genes coding for each QS system. Double mutants were obtained by simultaneous inactivation of genes coding for both QS systems. Most of the D. solani mutants showed an attenuation of chicory maceration and a decreased production of plant cell wall-degrading enzymes (PCWDEs) and motility, but to different degrees depending on the strain. The VFM-QS system seems to regulate virulence in both D. solani and Dickeya dadantii, but the AHL-QS system has greater effects in D. solani than in D. dadantii. The inactivation of both QS systems in D. solani did not reveal any additive effect on the tested features. The inactivation of vfm genes generally has a more dominant effect relative to that of exp genes. Thus, VFM- and AHL-QS systems do not work in synergy to modulate the production of diverse virulence factors and the ability to macerate plant tissue.

Regulators Involved in Dickeya solani Virulence, Genetic Conservation and Functional Variability.

Bacteria from the genus Dickeya (formerly Erwinia chrysanthemi) are plant pathogens causing severe diseases in many economically important crops. A majority of the strains responsible for potato disease in Europe belong to a newly identified Dickeya solani species. Although some ecological and epidemiological studies have been carried out, little is known about the regulation of D. solani virulence. The characterization of four D. solani strains indicates significant differences in their virulence on potato although they are genetically similar based on genomic fingerprinting profiles. A phenotypic examination included an analysis of virulence on potato, growth rate in culture, motility, Fe3+ chelation, and pectate lyase, cellulase, protease, biosurfactant and blue pigment production. Mutants of four D. solani strains were constructed by inactivating the genes coding either for one of the main negative regulators of D. dadantii virulence (kdgR, pecS and pecT) or for the synthesis and perception of signaling molecules (expI and expR). Analysis of these mutants indicated that PecS, PecT and KdgR play a similar role in both species, repressing to different degrees the synthesis of virulence factors. The thermoregulator PecT seems to be a major regulator of D. solani virulence. This work also reveals the role of quorum sensing mediated by ExpI and ExpR in D. solani virulence on potato.

Regulators Involved in Dickeya solani Virulence, Genetic Conservation and Functional Variability.

Bacteria from the genus Dickeya (formerly Erwinia chrysanthemi) are plant pathogens causing severe diseases in many economically important crops. A majority of the strains responsible for potato disease in Europe belong to a newly identified Dickeya solani species. Although some ecological and epidemiological studies have been carried out, little is known about the regulation of D. solani virulence. The characterization of four D. solani strains indicates significant differences in their virulence on potato although they are genetically similar based on genomic fingerprinting profiles. A phenotypic examination included an analysis of virulence on potato, growth rate in culture, motility, Fe3+ chelation, and pectate lyase, cellulase, protease, biosurfactant and blue pigment production. Mutants of four D. solani strains were constructed by inactivating the genes coding either for one of the main negative regulators of D. dadantii virulence (kdgR, pecS and pecT) or for the synthesis and perception of signaling molecules (expI and expR). Analysis of these mutants indicated that PecS, PecT and KdgR play a similar role in both species, repressing to different degrees the synthesis of virulence factors. The thermoregulator PecT seems to be a major regulator of D. solani virulence. This work also reveals the role of quorum sensing mediated by ExpI and ExpR in D. solani virulence on potato.

Regulators involved in Dickeya solani virulence, genetic conservation, and functional variability.

Bacteria from the genus Dickeya (formerly Erwinia chrysanthemi) are plant pathogens causing severe diseases in many economically important crops. A majority of the strains responsible for potato disease in Europe belong to a newly identified Dickeya solani species. Although some ecological and epidemiological studies have been carried out, little is known about the regulation of D. solani virulence. The characterization of four D. solani strains indicates significant differences in their virulence on potato, although they are genetically similar based on genomic fingerprinting profiles. A phenotypic examination included an analysis of virulence on potato; growth rate in culture; motility; Fe3+ chelation; and pectate lyase, cellulase, protease, biosurfactant, and blue pigment production. Mutants of four D. solani strains were constructed by inactivating the genes coding either for one of the main negative regulators of D. dadantii virulence (kdgR, pecS, and pecT) or for the synthesis and perception of signaling molecules (expI and expR). Analysis of these mutants indicated that PecS, PecT, and KdgR play a similar role in both species, repressing, to different degrees, the synthesis of virulence factors. The thermoregulator PecT seems to be a major regulator of D. solani virulence. This work also reveals the role of quorum sensing mediated by ExpI and ExpR in D. solani virulence on potato.

Bacterial pectate lyases, structural and functional diversity.

Pectate lyases are enzymes involved in plant cell wall degradation. They cleave pectin using a ß-elimination mechanism, specific for acidic polysaccharides. They are mainly produced by plant pathogens and plant-associated organisms, and only rarely by animals. Pectate lyases are also commonly produced in the bacterial world, either by bacteria living in close proximity with plants or by gut bacteria that find plant material in the digestive tract of their hosts. The role of pectate lyases is essential for plant pathogens, such as Dickeya dadantii, that use a set of pectate lyases as their main virulence factor. Symbiotic bacteria produce their own pectate lyases, but they also induce plant pectate lyases to initiate the symbiosis. Pectin degradation products may act as signals affecting the plant­bacteria interactions. Bacterial pectate lyases are also essential for using the pectin of dead or living plants as a carbon source for growth. In the animal gut, Bacteroides pectate lyases degrade the pectin of ingested food, and this is particularly important for herbivores that depend on their microflora for the digestion of pectin. Some human pathogens, such as Yersinia enterocolitica, produce a few intracellular pectate lyases that can facilitate their growth in the presence of highly pectinolytic bacteria, at the plant surface, in the soil or in the animal gut.

A family 3 glycosyl hydrolase of Dickeya dadantii 3937 is involved in the cleavage of aromatic glucosides.

Dickeya dadantii is a phytopathogenic bacterium secreting a large array of plant-cell-wall-degrading enzymes that participate in the infection and maceration of the host plant tissue. Sequencing of the D. dadantii 3937 genome predicted several genes encoding potential glycosidases. One of these genes, bgxA, encodes a protein classified in family 3 of glycosyl hydrolases. Inactivation of bgxA and the use of a gene fusion revealed that this gene is not essential for D. dadantii pathogenicity but that it is expressed during plant infection. The bgxA expression is induced in the presence of glycosidic or non-glycosidic aromatic compounds, notably ferulic acid, cinnamic acid, vanillic acid and salicin. The BgxA enzyme has a principal ß-d-glucopyranosidase activity and a secondary ß-d-xylopyranosidase activity (ratio 70 : 1). This enzyme activity is inhibited by different aromatic glycosides or phenolic compounds, in particular salicin, arbutin, ferulic acid and vanillic acid. Together, the induction effects and the enzyme inhibition suggest that BgxA is mostly involved in the cleavage of aromatic ß-glucosides. There is evidence of functional redundancy in the D. dadantii ß-glucoside assimilation pathway. In contrast to other ß-glucoside assimilation systems, involving cytoplasmic phospho-ß-glucosidases, the cleavage of aromatic glucosides in the periplasmic space by BgxA may avoid the release of a toxic phenolic aglycone into the cytoplasm while still allowing for catabolism of the glucose moiety.