Massive Survey on Bacterial-Bacteriophages Biodiversity and Quality of Natural Whey Starter Cultures in Trentingrana Cheese Production.

Andrea Merz,Elena Franciosi,Andrea Goss,Nicola Cologna,Ilaria Carafa,Miriam Zago,Maria Cid Rodriguez,Kieran Tuohy,Andrea Mancini

doi:10.3389/fmicb.2021.678012

Andrea Merz, Elena Franciosi + Show 7 more

Open Access

https://doi.org/10.3389/fmicb.2021.678012

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Abstract

This study focused on the microbial and bacteriophages identification and characterization in cheese-production facilities that use natural whey starter (NWS) cultures for Trentingrana production. Bacterial and phage screening was carried out on cooked not acidified whey and NWS samples isolated from six dairy factories, for 4 consecutive days in four different months. By means of a combined approach, using plate counts, bacterial isolation, and metataxonomic analysis Lactobacillus helveticus was found occurring as the dominant species in NWS cultures and Levilactobacillus brevis as codominant in the cheese factories where the temperature of NWS production was mainly lower than 40°C, suggesting that the variability in the parameters of the NWS culture preparation could differently modulate the bacterial species in NWS cultures. Using turbidity test approach on 303 bacterial isolates from the NWS cultures, 120 distinct phages were identified. L. helveticus phage contamination of NWS cultures was revealed in most of the analyzed samples, but despite the great recovery of bacteriophage contamination cases, the microbial quality of NWS cultures was high. Our results support the presence of natural bacteriophage resistance mechanisms in L. helveticus. The use of NWS cultures probably creates an ideal environment for the proliferation of different L. helveticus strains balanced with their phages without a clear dominance. It is evident, from this study, that the presence of a high biodiversity of NWS bacterial strains is relevant to avoid phages dominance in NWS cultures and consequently to keep a good acidification ability.

Highlights

Traditional and artisanal cheese productions are often based on fermentation processes carried on by defined starter cultures used to achieve defined and typical flavors and/or textures (Gatti et al, 2014; Gobbetti et al, 2018b)
The bacterial consortia are characterized by a lower species complexity but high degree of strains diversity (Erkus et al, 2013), and bacteriophages have a regulatory role in the bacterial population dynamics through density-dependent predation (Rodriguez-Valera et al, 2009)
This study was carried out to investigate the bacterial and phage dynamics of cooked not acidified whey (cNAW) and natural whey starter (NWS) production analyzing samples collected in 72 different days of Trentingrana production in six dairy plants, over a year period, by means of a combined approach, using plate counts, bacterial isolation, metataxonomic analysis, and phage isolation

Summary

Introduction

Traditional and artisanal cheese productions are often based on fermentation processes carried on by defined starter cultures used to achieve defined and typical flavors and/or textures (Gatti et al, 2014; Gobbetti et al, 2018b). Refreshed daily in the dairy factory from whey collected at the end of the cheese-making process (Bertani et al, 2020), these starters are mainly characterized by thermophilic lactic acid bacteria (LABs) such as Lactobacillus helveticus, Lactobacillus delbrueckii ssp. Together with raw milk quality, bacteriophages (or phages) may represent a dealing factor able to negatively affect fitness and performance of dairy starter cultures (Carminati et al, 2011). The most permanent source of phage in dairy is the raw milk, and considering that Trentingrana dairy factories use raw milk in cheese production, they can rapidly grow up to high concentration in NWS cultures (Guglielmotti et al, 2012)

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