Effects of Xenorhabdus and Photorhabdus (Morganellaceae) on volatile composition of “Tempranillo” must and on Saccharomyces cerevisiae during alcoholic fermentation

Viticulture is a global activity producing over eighty million tonnes of grapes annually, 50 % used in winemaking. Traditional viticultural practices still rely on hazardous pesticides, posing environmental and health risks. Recently, Xenorhabdus and Photorhabdus, symbiotic bacteria of entomopathogenic nematodes, have arisen as eco-friendly solutions for pest and disease management in vineyards. However, whether their application can impact the quality of grapes and their microbiota remains unexplored. To unravel the possible impact, we investigated the effect of (i) their direct application on grapes’ volatile composition and (ii) their combination with Saccharomyces cerevisiae in must fermentation. First, we applied unfiltered ferments (UFs) of Xenorhabdus nematophila and Photorhabdus laumondii subsp. laumondii to grapes of Vitis vinifera var. “Tempranillo”. The volatile composition of the grapes was evaluated using solid-phase and gas chromatography-mass spectrometry (SPE-GC/MS). Second, microfermentations using two S. cerevisiae in reconstituted must media were supplemented (1:10) with the treatments (i) cell-free supernatants (CFS), (ii) UFs, and (iii) free-bacterial from X. nematophila and P. laumondii. No significant alterations in the total free volatile fraction were observed, although specific free volatiles (phenyl ethyl alcohol, hexanal, and (E)-2-hexenal) exhibited significant variation under specific treatments. In the glycosidically bound fraction, phenylacetic acid concentrations increased markedly with X. nematophila UFs. In the fermentations, the treatments had no significant impact on CO2 production kinetics and only slightly affected some fermentation parameters, underscoring their compatibility with yeast-driven fermentation processes. These findings suggest that Xenorhabdus and Photorhabdus can be integrated into vineyard pest management strategies without adversely affecting winemaking parameters or grape aroma quality.