Genetic and Functional Diversity Help Explain Pathogenic, Weakly Pathogenic, and Commensal Lifestyles in the Genus Xanthomonas

The genus Xanthomonas has been primarily studied for pathogenic interactions with plants. However, besides host and tissue-specific pathogenic strains, this genus also comprises nonpathogenic strains isolated from a broad range of hosts, sometimes in association with pathogenic strains, and other environments, including rainwater. Based on their incapacity or limited capacity to cause symptoms on the host of isolation, nonpathogenic xanthomonads can be further characterized as commensal and weakly pathogenic. This study aimed to understand the diversity and evolution of nonpathogenic xanthomonads compared to their pathogenic counterparts based on their cooccurrence and phylogenetic relationship and to identify genomic traits that form the basis of a life history framework that groups xanthomonads by ecological strategies. We sequenced genomes of 83 strains spanning the genus phylogeny and identified eight novel species, indicating unexplored diversity. While some nonpathogenic species have experienced a recent loss of a type III secretion system, specifically the hrp2 cluster, we observed an apparent lack of association of the hrp2 cluster with lifestyles of diverse species. We performed association analysis on a large data set of 337 Xanthomonas strains to explain how xanthomonads may have established association with the plants across the continuum of lifestyles from commensals to weak pathogens to pathogens. Presence of distinct transcriptional regulators, distinct nutrient utilization and assimilation genes, transcriptional regulators, and chemotaxis genes may explain lifestyle-specific adaptations of xanthomonads.

Pectin as Carbon Source for Monilinia laxa Exoproteome and Expression Profiles of Related Genes

Pectin, as part of the fruit cell wall, can be degraded by brown rot fungi by coordinating the production, secretion, and action of extracellular enzymes. In this study, pectin utilization by the necrotroph Monilinia laxa 8L was studied by in vitro and in silico approaches. A total of 403 genes encoding carbohydrate-active enzymes (CAZymes) were identified, including 38 coding a predicted pectin-degrading activity. Analyzing the differences between M. laxa 8L exoproteomes in media containing glucose and pectin as sole carbon sources, we identified 107 pectin-specific proteins, among them, 64.48% harbor a classical secretory activity, including 42 CAZymes and six pectin-degrading proteins. Analyzing the gene-expression patterns of some pectinase families revealed their possible sequential action in pectin disassembly. We found, in vitro, an early pectin-dependent induction of MlRGAE1, MlPG1, and three members of the rhamnosidase family (MlαRHA2, MlαRHA3, and MlαRHA6) and late response of MlPG2 and MlPNL3. M. laxa 8L has the ability to use both pectin and byproducts as carbon sources, based on a functional pectinolytic machinery encoded in its genome, subjected to pectin-dependent regulation and appropriate secretion mechanisms of these pectinolytic enzymes. Differences in the secretion and transcription profile of M. laxa 8L provided insights into the different mechanisms that contribute to brown rot development.

Rye Bran Modified with Cell Wall-Degrading Enzymes Influences the Kinetics of Plant Lignans but Not of Enterolignans in Multicatheterized Pigs

Background: Whole-grain intake is associated with a lower risk of chronic Western-style diseases, possibly brought about by the high concentration of phytochemicals, among them plant lignans (PLs), in the grains.Objective: We studied whether treatment of rye bran with cell wall-degrading enzymes changed the solubility and kinetics of PLs in multicatheterized pigs.Methods: Ten female Duroc × Danish Landrace × Yorkshire pigs (60.3 ± 2.3 kg at surgery) fitted with permanent catheters were included in an incomplete crossover study. The pigs were fed 2 experimental diets for 1-7 d. The diets were rich in PLs and based on nontreated lignan-rich [LR; lignan concentration: 20.2 mg dry matter (DM)/kg] or enzymatically treated lignan-rich (ENZLR; lignan concentration: 27.8 mg DM/kg) rye bran. Plasma concentrations of PLs and enterolignans were quantified with the use of targeted LC-tandem mass spectrometry. Data were log transformed and analyzed with mixed-effects, 1-compartment, and asymptotic regression models.Results: The availability of PLs was 38% greater in ENZLR than in LR, and the soluble fraction of PLs was 49% in ENZLR compared with 35% in LR diets. PLs appeared in the circulation 30 min after intake of both the ENZLR and LR diets. Postprandially, consumption of ENZLR resulted in a 4-times-greater (P < 0.0001) plasma PL concentration compared with LR. The area under the curve (AUC) measured 0-360 min after ENZLR intake was ∼2 times higher than after LR intake. A 1-compartment model could describe the postprandial increase in plasma concentration after ENZLR intake, whereas an asymptotic regression model described the plasma concentrations after LR intake. Despite increased available and soluble PLs, ENZLR did not increase plasma enterolignans.Conclusion: The modification of rye bran with cell wall-degrading enzymes resulted in significantly greater plasma concentrations of PLs and the 4-h AUC, particularly syringaresinol, in multicatheterized pigs.