Xyloglucans are highly substituted and recalcitrant polysaccharides found in the primary cell walls of vascular plants, acting as a barrier against pathogens. Here, we reveal that the diverse and economically relevant Xanthomonas bacteria are endowed with a xyloglucan depolymerization machinery that is linked to pathogenesis. Using the citrus canker pathogen as a model organism, we show that this system encompasses distinctive glycoside hydrolases, a modular xyloglucan acetylesterase and specific membrane transporters, demonstrating that plant-associated bacteria employ distinct molecular strategies from commensal gut bacteria to cope with xyloglucans. Notably, the sugars released by this system elicit the expression of several key virulence factors, including the type III secretion system, a membrane-embedded apparatus to deliver effector proteins into the host cells. Together, these findings shed light on the molecular mechanisms underpinning the intricate enzymatic machinery of Xanthomonas to depolymerize xyloglucans and uncover a role for this system in signaling pathways driving pathogenesis.

Aim To characterize the proteome of 20 root canals in teeth with post‐treatment endodontic disease using mass spectrometry and to correlate the identified proteins with clinical features. Methodology Twenty patients with radiographic evidence of apical periodontitis and need for root canal re‐treatment were selected. Samples from the root canal contents were collected and processed using two‐dimensional capillary nano‐flow liquid chromatography and electrospray ionization tandem mass spectrometry. The acquired spectra were separately searched against specific protein database. The results obtained were analysed using descriptive statistics. Additionally, Pearson's chi‐square test or one‐sided Fisher's exact test, as appropriate, was chosen to examine the null hypothesis that there is no relationship between each clinical feature and the presence of specific microbial or human proteins. Significance levels were set at 5% (P < 0.05). Results A total of 1153 human and 720 microbial UniProt accession numbers corresponding to proteins were recovered. The greater prevalence of proteins was related to biological functions, such as cellular and metabolic processes. A considerable number of microbial proteins with clinical relevance functions, such as pathogenesis/virulence, proteolysis, cell adhesion and drug resistance, were detected. Common endodontic pathogens related to post‐treatment endodontic disease such as Enterococcus spp., Propionibacterium spp. and Streptococcus spp. were associated with 23, 40 and 94 distinct proteins, respectively. As for human proteins, many factors related to the immune system process were detected. No significant correlations were found between microbial and human proteins and the clinical features investigated (P > 0.05). Conclusions A considerable number of microbial and human proteins were identified using proteomic analyses, being mainly related to processes indicating cell viability. No significant correlation was found between proteins and clinical features. These findings suggest a network of important microbial pathogenic functions that may be responsible for the host immune system response.

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