Attachment of Salmonella strains to a plant cell wall model is modulated by surface characteristics and not by specific carbohydrate interactions

Background: Processing of fresh produce exposes cut surfaces of plant cell walls that then become vulnerable to human foodborne pathogen attachment and contamination, particularly by Salmonella enterica. Plant cell walls are mainly composed of the polysaccharides cellulose, pectin and hemicelluloses (predominantly xyloglucan). Our previous work used bacterial cellulose-based plant cell wall models to study the interaction between Salmonella and the various plant cell wall components. We demonstrated that Salmonella attachment was favoured in the presence of pectin while xyloglucan had no effect on its attachment. Xyloglucan significantly increased the attachment of Salmonella cells to the plant cell wall model only when it was in association with pectin. In this study, we investigate whether the plant cell wall polysaccharides mediate Salmonella attachment to the bacterial cellulose-based plant cell wall models through specific carbohydrate interactions or through the effects of carbohydrates on the physical characteristics of the attachment surface. Results: We found that none of the monosaccharides that make up the plant cell wall polysaccharides specifically inhibit Salmonella attachment to the bacterial cellulose-based plant cell wall models. Confocal laser scanning microscopy showed that Salmonella cells can penetrate and attach within the tightly arranged bacterial cellulose network. Analysis of images obtained from atomic force microscopy revealed that the bacterial cellulose-pectin-xyloglucan composite with 0.3 % (w/v) xyloglucan, previously shown to have the highest number of Salmonella cells attached to it, had significantly thicker cellulose fibrils compared to other composites. Scanning electron microscopy images also showed that the bacterial cellulose and bacterial cellulose-xyloglucan composites were more porous when compared to the other composites containing pectin. Conclusions: Our study found that the attachment of Salmonella cells to cut plant cell walls was not mediated by specific carbohydrate interactions. This suggests that the attachment of Salmonella strains to the plant cell wall models were more dependent on the structural characteristics of the attachment surface. Pectin reduces the porosity and space between cellulose fibrils, which then forms a matrix that is able to retain Salmonella cells within the bacterial cellulose network. When present with pectin, xyloglucan provides a greater surface for Salmonella cells to attach through the thickening of cellulose fibrils

Physiological and cell ultrastructure disturbances in wheat seedlings generated by Chenopodium murale hairy root exudate.

Chenopodium murale L. is an invasive weed species significantly interfering with wheat crop. However, the complete nature of its allelopathic influence on crops is not yet fully understood. In the present study, the focus is made on establishing the relation between plant morphophysiological changes and oxidative stress, induced by allelopathic extract. Phytotoxic medium of C. murale hairy root clone R5 reduced the germination rate (24% less than control value) of wheat cv. Nataša seeds, as well as seedling growth, diminishing shoot and root length significantly, decreased total chlorophyll content, and induced abnormal root gravitropism. The R5 treatment caused cellular structural abnormalities, reflecting on the root and leaf cell shape and organization. These abnormalities mostly included the increased number of mitochondria and reorganization of the vacuolar compartment, changes in nucleus shape, and chloroplast organization and distribution. The most significant structural changes were observed in cell wall in the form of amoeboid protrusions and folds leading to its irregular shape. These structural alterations were accompanied by an oxidative stress in tissues of treated wheat seedlings, reflected as increased level of H2O2 and other ROS molecules, an increase of radical scavenging capacity and total phenolic content. Accordingly, the retardation of wheat seedling growth by C. murale allelochemicals may represent a consequence of complex activity involving both cell structure alteration and physiological processes.This is a post-peer-review, pre-copyedit version of an article published in Protoplasma. The final authenticated version is available online at: [http://dx.doi.org/10.1007/s00709-018-1250-0

Genetic analysis of bread-making quality scores in bread wheat using a recombinant inbred line population

Bread-making quality has been evaluated in a progeny of 194 recombinant inbred lines (RILs) from the cross between the two French cultivars Recital and Renan, cultivated in three environments. These cultivars have been previously identified as having contrasting grain protein content and dough rheology properties, although they achieve similar scores for the official bread-making test used for cultivar registration in France. However the progeny displayed a wide range of variations, suggesting that favourable alleles at several loci are present in the two parental lines. Correlation analyses revealed that bread-making scores are poorly correlated among environments, as they are poorly predicted by multiple regression on dough rheology parameters and flour-protein content. However, loaf volume was the most heritable and predictable trait. A total of seven QTLs were found for bread scores, each explaining 5.9-14.6% of trait variation and six for the loaf volume (10.7-17.2%). Most bread-making QTLs, and particularly those detected in all environments, co-located with QTLs for dough rheology, protein content or flour viscosity due to soluble pentosans (Fincher and Stone 1986; Anderson et al. in J Cereal Sci 19:77-82, 1994). Some QTL regions such as those on chromosome 3A and chromosome 7A, which display stable QTLs for bread-making scores and loaf volume, were not previously known to host obvious genes for grain quality

Influence of Polysaccharide Composition on the Structure and Properties of Cellulose-based Composites

Plant cell walls are Nature’s most abundant source of organic polymers, making them a prime candidate for technologies based on renewable raw material resources. The bulk of cell wall material is in the form of so-called secondary cell walls, characteristic of woody tissues and used in, e.g. construction and paper industries. Primary cell walls are characteristic of growing and fleshy plant tissues, and contain several different polymer types that find specialised uses in food and other applications. As the mysteries of biological control of cell wall composition start to be unravelled by functional genomics and related approaches, it is timely to consider how best to make use of the tremendous natural resource presented by plant cell walls. This contribution will address (i) compositional diversity, (ii) principles of wall assembly and (iii) effects of individual polymers on primary cell wall material properties, taking advantage of a model system based on bacterial cellulose

Tensile deformation of Bacterial Cellulose composites

The polymeric basis for the mechanical properties of primary plant cell walls has been investigated by forming analogous composites based on fermentation of the bacterium Acetobacter xylinus, either alone or in the presence of xyloglucan or pectin. Simultaneous small-angle X-ray scattering and uniaxial deformation experiments has shown how the cellulose microfibrils reorient during deformation. Despite very different stress/strain curves, the reorientation behaviour is similar, regardless of the presence or absence of xyloglucan or pectin. A simple theory has been developed to predict the orientation behaviour. This is qualitatively similar to the measured behaviour, but differs quantitatively. (C) 2003 Elsevier Science B.V. All rights reserved

Structure of Acetobacter cellulose composites in the hydrated state

The structure of composites produced by the bacterium Acetobacter xylinus have been studied in their natural. hydrated. state. Small-angle X-ray diffraction and environmental scanning electron microscopy has shown that the ribbons have a width of 500 A and contain smaller semi-crystalline cellulose microfibrils with an essentially rectangular cross-section of approximate to 10 x 160 Angstrom (2). Incubation of Acetobacter in xyloglucan or pectin results in no changes in the size of either the microfibrils or the ribbons. Changes in the cellulose crystals are seen upon dehydration of the material, resulting in either a reduction in crystal size or an increase in crystal disorder. (C) 2001 Published by Elsevier Science B.V

Mechanical effects of plant cell wall enzymes on xyloglucan/cellulose composites

Xyloglucan-acting enzymes are believed to have effects on type I primary plant cell wall mechanical properties. In order to get a better understanding of these effects, a range of enzymes with different in vitro modes of action were tested against cell wall analogues (bio-composite materials based on Acetobacter xylinus cellulose and xyloglucan). Tomato pericarp xyloglucan endo transglycosylase (tXET) and nasturtium seed xyloglucanase (nXGase) were produced heterologously in Pichia pastoris. Their action against the cell wall analogues was compared with that of a commercial preparation of Trichoderma endo-glucanase (EndoGase). Both 'hydrolytic' enzymes (nXGase and EndoGase) were able to depolymerise not only the cross-link xyloglucan fraction but also the surface-bound fraction. Consequent major changes in cellulose fibril architecture were observed. In mechanical terms, removal of xyloglucan cross-links from composites resulted in increased stiffness (at high strain) and decreased visco-elasticity with similar extensibility. On the other hand, true transglycosylase activity (tXET) did not affect the cellulose/xyloglucan ratio. No change in composite stiffness or extensibility resulted, but a significant increase in creep behaviour was observed in the presence of active tXET. These results provide direct in vitro evidence for the involvement of cell wall xyloglucan-specific enzymes in mechanical changes underlying plant cell wall re-modelling and growth processes. Mechanical consequences of tXET action are shown to be complimentary to those of cucumber expansin

Genetic variability and stability of grain magnesium, zinc and iron concentrations in bread wheat

Four trials were conducted to study the grain magnesium (Mg), zinc (Zn) and iron (Fe) concentrations in bread wheat (Triticum aestivum L.). These trials used different sources of genotypes, including old French landraces, a worldwide germplasm collection and elite breeding lines or modem cultivars, grown in different environments. Mg concentration ranged from 600 to 1400 ppm in modem material, and reached 1890 ppm in some exotic genotypes. There was a negative correlation between grain yield and Mg concentration, but despite this dilution effect enough variability remains useful for selection purposes. Analysis of variance showed high genotype effects and Spearman rank correlations indicated moderate genotype by environment (G x E) interactions, so breeding for high Mg concentration can reasonably be envisaged. Zn concentration generally ranged from 15 to 35 ppm, but increased to 43 ppm in some genetic resources. Variation in Zn was also partly explained by a dilution effect. There was a significant effect of genotype, but also high G x E interactions, which would make direct selection more difficult than for Mg. However, as Zn and Mg concentrations appeared to be positively correlated, Zn concentration should respond favorably to selection for high Mg concentration. Fe concentration ranged from 20 to 60 ppm, and reached 88 ppm in non-adapted material. There were no significant genotype effects, very high G x E interactions, and the trait was poorly correlated to other mineral concentrations. Breeding for high Fe concentration will thus probably prove illusory