The role of Ovotransferrin in egg-white antimicrobial activity: a review

Eggs are a whole food which affordably support human nutritional requirements worldwide. Eggs strongly resist bacterial infection due to an arsenal of defensive systems, many of which reside in the egg white. However, despite improved control of egg production and distribution, eggs remain a vehicle for foodborne transmission of Salmonella enterica serovar Enteritidis, which continues to represent a major public health challenge. It is generally accepted that iron deficiency, mediated by the iron-chelating properties of the egg-white protein ovotransferrin, has a key role in inhibiting infection of eggs by Salmonella. Ovotransferrin has an additional antibacterial activity beyond iron-chelation, which appears to depend on direct interaction with the bacterial cell surface, resulting in membrane perturbation. Current understanding of the antibacterial role of ovotransferrin is limited by a failure to fully consider its activity within the natural context of the egg white, where a series relevant environmental factors (such as alkalinity, high viscosity, ionic composition, and egg white protein interactions) may exert significant influence on ovotransferrin activity. This review provides an overview of what is known and what remains to be determined regarding the antimicrobial activity of ovotransferrin in egg white, and thus enhances understanding of egg safety through improved insight of this key antimicrobial component of eggs

Environmental conditions and molecular fractions involved in the antimicrobial activity of egg white against S. Enteritidis

In Europe, the species Salmonella enterica, particularly the serovar S. Enteritidis, represents the major human pathogen related to egg consumption. Consequently, it is mainly used as a model in most studies interested in the antimicrobial activity of egg white. In order to explain this antimicrobial activity, the main hypotheses are, on the one hand, the involvement of antimicrobial egg white proteins (ovotransferrin, lysozyme…), and, on the other hand, physicochemical factors such as alkaline pH, and viscous and heterogeneous structure. However, data are conflicting in the literature, and it is difficult to compare the studies because of the use of various strains, various inoculum sizes, various incubation times and temperatures and eggs with varying freshness.Hence, we have investigated the incubation conditions enhancing the antimicrobial activity of egg white against S. Enteritidis by carrying a complete factorial design analysis comprising 180 experimental conditions. Three different media were chosen in order to evaluate the effect of the macromolecular fraction of egg white: whole egg white, egg white filtrate, and egg white filtrate supplemented with 10 % egg white. The other tested factors were the temperature (37°C to 48°C), pH (9.3 versus 7.8) and initial inoculum size (3 to 8 log cfu.mL-1). This study clearly identified the temperature and the presence of macromolecules as the main factors involved in the bactericidal activity of egg white against S. Enteritidis

Dry heating of lysozyme: strong effects regarding antimicrobial activity

International audienceFor food preservation as well as for medical applications, because of increasing bacterial resistance towards antibiotics, novel and natural antimicrobial molecules are request. The widely studied lysozyme is a promising candidate to develop such molecules. This protein is well known and already used for its enzymatic activity against Gram-positive bacteria, but it also presents some activity against Gram-negative bacteria, supposedly due to its capability to disturb bacteria membrane. Otherwise, molecules that provoke bacterial membrane disruption are generally positively charged, amphipathic, and hydrophobic, all characteristics which can be modified. Especially, we previously showed that dry heating is a safe and easy process resulting in slight chemical modifications of lysozyme, with strong consequences regarding the charge, the hydrophobicity, and finally the interfacial properties of the protein. The question then arose: could lysozyme dry heating be an opportunity to create a new efficient antimicrobial? We actually demonstrated that the activity of dry heated lysozyme (DH-L) against Escherichia coli was higher than that of native lysozyme (N-L). Using optical microscopy and atomic force microscopy (AFM), strong morphological modifications of the bacteria were observed, consistently with the higher membrane permeabilization when E. coli cells were treated with DH-L: either larger pores or more pores in the outer membrane, as well as more ion channels in the cytoplasmic membrane were obtained with DH-L as compared to N-L. Using a lipopolysaccharide (LPS) monolayer and a phospholipid (PL) mixture monolayer as models of the E. coli outer and cytoplasmic membranes, respectively, the interaction between lysozyme and these monolayer models has been investigated by biophysics techniques such as tensiometry, ellipsometry, Brewster angle microscopy and AFM. We could thus established that dry heating increases lysozyme affinity for the model monolayers and its insertion capacity; the resulting reorganization of the model monolayers was also more drastic. Finally, using similar investigations with each of the lysozyme isoforms produced by dry heating, we could show that the most positive, flexible and hydrophobic isoform shows the highest antimicrobial activity. However, it is noticeable that the lysozyme isoforms mixture, I;e; DH-L was the most efficient against E. coli, suggesting synergetic cooperation between lysozyme isoforms

The MPK8-TCP14 pathway promotes seed germination in Arabidopsis

[EN] The accurate control of dormancy release and germination is critical for successful plantlet establishment. Investigations in cereals hypothesized a crucial role for specific MAP kinase (MPK) pathways in promoting dormancy release, although the identity of the MPK involved and the downstream events remain unclear. In this work, we characterized mutants for Arabidopsis thaliana MAP kinase 8 (MPK8). Mpk8 seeds presented a deeper dormancy than wild-type (WT) at harvest that was less efficiently alleviated by after-ripening and gibberellic acid treatment. We identified Teosinte Branched1/Cycloidea/Proliferating cell factor 14 (TCP14), a transcription factor regulating germination, as a partner of MPK8. Mpk8 tcp14 double-mutant seeds presented a deeper dormancy at harvest than WT and mpk8, but similar to that of tcp14 seeds. MPK8 interacted with TCP14 in the nucleus in vivo and phosphorylated TCP14 in vitro. Furthermore, MPK8 enhanced TCP14 transcriptional activity when co-expressed in tobacco leaves. Nevertheless, the stimulation of TCP14 transcriptional activity by MPK8 could occur independently of TCP14 phosphorylation. The comparison of WT, mpk8 and tcp14 transcriptomes evidenced that whereas no effect was observed in dry seeds, mpk8 and tcp14 mutants presented dramatic transcriptomic alterations after imbibition with a sustained expression of genes related to seed maturation. Moreover, both mutants exhibited repression of genes involved in cell wall remodeling and cell cycle G1/S transition. As a whole, this study unraveled a role for MPK8 in promoting seed germination, and suggested that its interaction with TCP14 was critical for regulating key processes required for germination completion.This work was supported by the Chinese Scholarship Council (201606690037 to WZ), CNRS, Sorbonne Universite and the LabEx Saclay Plant Sciences-SPS (ANR-10-LABX-0040-SPS). The authors acknowledge Jean Francois Gilles from the IBPS imaging core facility, which is supported by Conseil Regional Ile-de-France, for help with confocal microscopy. The authors thank Cristina Urbez (CSIC-U Politecnica de Valencia) for technical assistance. The authors thank Pr Brendan Davies (University of Leeds) for providing tcp14.4 seeds, and Dr Jean Colcombet (IPS2 Universite Paris-Saclay) for providing MPK8-pDONOR vector.Zhang, W.; Cochet, F.; Ponnaiah, M.; Lebreton, S.; Matheron, L.; Pionneau, C.; Boudsocq, M.... (2019). The MPK8-TCP14 pathway promotes seed germination in Arabidopsis. The Plant Journal. 100(4):677-692. https://doi.org/10.1111/tpj.14461S6776921004Barrôco, R. M., Van Poucke, K., Bergervoet, J. H. W., De Veylder, L., Groot, S. P. C., Inzé, D., & Engler, G. (2005). The Role of the Cell Cycle Machinery in Resumption of Postembryonic Development. 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Antimicrobial activity of lysozyme isoforms: Key molecular features

International audienceIncreasing bacterial resistance towards antibiotics has stimulated research for novel antimicrobials. Proteins acting on bacterial membranes could be a solution. Lysozyme has been proven active against E. coli by disruption of both outer and cytoplasmic membranes, with dry-heating increasing lysozyme activity. Dry-heated lysozyme (DH-L) is a mixture of isoforms (isoaspartyl, native-like and succinimide lysozymes), giving rise to two questions: what effects does each form have, and which physicochemical properties are critical as regards the antibacterial activity? These issues were investigated by fractionating DH-L, analyzing structural properties of each fraction, and testing each fraction in vivo on bacteria and in vitro on membrane models. Positive net charge, hydrophobicity and molecular flexibility of the isoforms seem key parameters for their interaction with E. coli membranes. The succinimide lysozyme fraction, the most positive, flexible and hydrophobic, shows the highest antimicrobial activity, induces the strongest bacterial membrane disruption and is the most surface active on model lipid monolayers. Moreover, each fraction appears less efficient than DH-L against E. coli, indicating a synergetic cooperation between lysozyme isoforms. The bacterial membrane modifications induced by one isoform could facilitate the subsequent action of the other isoforms