Phage Biodiversity in Artisanal Cheese Wheys Reflects the Complexity of the Fermentation Process.

Jennifer Mahony,Gabriele Lugli,Luca Settanni,Marco Ventura,Philip Kelleher,Douwe Van Sinderen,Angelo Moscarelli

doi:10.3390/v9030045

Jennifer Mahony, Gabriele Lugli + Show 5 more

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https://doi.org/10.3390/v9030045

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Abstract

Dairy fermentations constitute a perfect “breeding ground” for bacteriophages infecting starter cultures, particularly strains of Lactococcus lactis. In modern fermentations, these phages typically belong to one of three groups, i.e., the 936, P335, and c2 phage groups. Traditional production methods present fewer chemical and physical barriers to phage proliferation compared to modern production systems, while the starter cultures used are typically complex, variable, and undefined. In the current study, a variety of cheese whey, animal-derived rennet, and vat swab samples from artisanal cheeses produced in Sicily were analysed for the presence of lactococcal phages to assess phage diversity in such environments. The complete genomes of 18 representative phage isolates were sequenced, allowing the identification of 10 lactococcal 949 group phages, six P087 group phages, and two members of the 936 group phages. The genetic diversity of these isolates was examined using phylogenetic analysis as well as a focused analysis of the receptor binding proteins, which dictate specific interactions with the host-encoded receptor. Thermal treatments at 63 °C and 83 °C indicate that the 949 phages are particularly sensitive to thermal treatments, followed by the P087 and 936 isolates, which were shown to be much less sensitive to such treatments. This difference may explain the relatively low frequency of isolation of the so-called “rare” 949 and P087 group phages in modern fermentations.

Highlights

In modern dairy fermentation facilities, plant design, bacterial starter cultures, sanitation regime, equipment and materials are all carefully chosen, monitored and controlled in order to limit production inconsistencies and achieve optimal product output
To assess if a link exists between the dominant phage groups isolated from various whey samples and the raw milk used in its production, we examined the groups of phages isolated from the different cheese wheys. 949 group phages were isolated from Canestrato, Vastedda and Caciocavallo cheese wheys indicating their widespread presence in all cheese types irrespective of the source of the milk or factory site tested
While defined cultures may employed in the production of artisan cheeses, in many cases the autochthonous bacteria present in the sometimes be employed in the production of artisan cheeses, in many cases the autochthonous fermentation environment are responsible for the acidification and development of the derived cheese

Summary

Introduction

In modern dairy fermentation facilities, plant design, bacterial starter cultures, sanitation regime, equipment and materials are all carefully chosen, monitored and controlled in order to limit production inconsistencies and achieve optimal product output. In such processes, the incoming raw milk is often subjected to thermal treatments, such as pasteurisation to reduce the microbial load followed by the deliberate introduction of selected starter bacteria or mixed cultures which acidify the milk and impart desirable organoleptic attributes upon the product. Beyond the biological hurdles presented in modern production facilities and procedures, the only major limitation to phage proliferation in traditional practices is the availability of a suitable host

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