Xanthomonas albilineans (Xa) and X. sacchari (Xs) are both sugarcane pathogens. Xa is the causal agent of leaf scald disease, but there is limited information about the pathogenicity of Xs. The aim of this work was to study virulence factors of native strains of Xa (Xa32, Xa33, and XaM6) and Xs (Xs14 and Xs15) previously isolated from sugarcane with leaf scald symptoms, to gain insight into the biology of each microorganism. We analysed epiphytic survival, sensitivity to oxidative stress, extracellular degradative enzymes, cell motilities, exopolysaccharide (EPS) characteristics, cell adhesion, biofilm development, and control of stomatal regulation of the five strains. We observed that each species presented similar phenotypes for every factor analysed. Xa strains appeared to be more sensitive to oxidative stress and presented lower epiphytic survival than Xs. All strains presented endoglucanase activity; however, we could only detect protease and amylase activities in Xs strains. Swimming and sliding were higher in Xs, but twitching was variable among species. We also observed that only Xs strains produced a xanthan‐like EPS, presented a strong cell adhesion, and structured biofilm. We detected some intraspecific variations showing that higher amounts of EPS produced by Xs14 correlated with its higher sliding motility and its homogenous and more adhesive biofilm. In addition, EPSs of Xs14 and Xs15 presented differences in strand height and acetyl percentage. Finally, we found that strains of both species were able to interfere with stomatal aperture mechanism. All these differences could influence the colonization strategies and/or disease progression in each species.
Psychrotroph microorganisms have developed cellular mechanisms to cope with cold stress. Cell envelopes are key components for bacterial survival. Outer membrane is a constituent of Gram negative bacterial envelopes, consisting of several components, such as lipopolysaccharides (LPS). In this work we investigated the relevance of envelope characteristics for cold adaptation in the Antarctic bacterium Pseudomonas extremaustralis by analyzing a mini Tn5 wapH mutant strain, encoding a core LPS glycosyltransferase. Our results showed that wapH strain is impaired to grow under low temperature but not for cold survival. The mutation in wapH, provoked a strong aggregative phenotype and modifications of envelope nanomechanical properties such as lower flexibility and higher turgor pressure, cell permeability and surface area to volume ratio (S/V). Changes in these characteristics were also observed in the wild type strain grown at different temperatures, showing higher cell flexibility but lower turgor pressure under cold conditions. Cold shock experiments indicated that an acclimation period in the wild type is necessary for cell flexibility and S/V ratio adjustments. Alteration in cell-cell interaction capabilities was observed in wapH strain. Mixed cells of wild type and wapH strains, as well as those of the wild type strain grown at different temperatures, showed a mosaic pattern of aggregation. These results indicate that wapH mutation provoked marked envelope alterations showing that LPS core conservation appears as a novel essential feature for active growth under cold conditions.
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