Unraveling molecular interactions between wine lactic acid bacteria, their viral predators, and polyphenols – WINE

Lactic acid bacteria (LAB)-infecting bacteriophages (phages, or bacterial viruses) use diverse host-binding mechanisms, yet the overall picture of the interactions between LAB phages and their host remains incomplete. Unraveling the molecular details of phage-LAB interactions is essential not only for decoding phage biology, but also for industrial and public health purposes since LAB are important micro-organisms in food fermentations and in the human gut microbiota. Phages infecting the LAB species Lactococcus lactis and Streptococcus thermophilus have enjoyed extensive scientific scrutiny since they may disrupt LAB-dependent processes in dairy plants with serious concomitant economic losses. In contrast, there is a significant knowledge gap on the interactions between plant-associated LAB and their phage, even though they may also significantly impact fermentation processes. This is true for fermented beverages as exemplified by the emblematic field of winemaking that heavily relies on the LAB species Oenococcus oeni. Recently, we have shown that representative phages that infect O. oeni possess host-binding devices of distinct composition and morphology, and being different from those of lactococcal and streptococcal phages, that likely employ novel host-binding mechanisms. Moreover, we have observed that wine polyphenolic compounds (PCs), which are abundant in the O. oeni ecological niche, can interfere with the phage infection process. These organic compounds, being sterically similar to cell surface saccharides recognized by phages, may occupy phage receptor-binding sites, thereby preventing host binding. Moreover, PCs could also induce modifications in the cell wall saccharide composition, which would also prevent phages from binding to their host.
In this context, our overall aim is to unravel molecular interactions between the wine LAB O. oeni, their viral predators, and PCs. We will work on three representative oenophages, all of which infect the same strain but use different host-binding devices differently affected by wine PCs. We will leverage complementary approaches covering the fields of structural biology, biochemistry, and microbiology, to meet our stated aim. We will 1) determine structure-function relationships of distinct host-binding devices combining cryo-electron microscopy, X-ray crystallography, biophysical characterization of protein-ligand interactions, and host cell-binding assays, 2) explore host-binding capabilities of these phages and the impact of PCs combining phenotypic analyses (generation of bacteriophage-insensitive mutants, phage plaque assays, adsorption tests) and comparative genomics, and 3) map phage-specific host cell saccharide receptors and examine the potential effects of PCs on the synthesis of these receptors through the analysis of gene expression, cell wall biochemical composition, and chemical structure of surface polysaccharides.
Investigating molecular interactions between the wine LAB O. oeni and its phages, as a model system of the interactions between plant-related LABs and their phages, will significantly advance current knowledge of phage biology and structure, while simultaneously defining the role and potential inhibitory action of plant PCs on phage infection. We will produce important knowledge of LAB-phage interactions with expected high gains for the wine industry, as well as other plant-fermented products. Of note, plant-based fermented products are currently one of the most innovative and dynamic food categories, in response to the increasing popularity of vegetarian and vegan diets in western countries. Lastly, addressing the role of plant PCs on phage-host interactions may also lead to a better understanding of gut microbiota dynamics and to the rational development of ‘green’ phage-based biocontrol strategies, thereby opening perspectives in the socio-economically important fields of human health and agriculture.