Effect of using mycotoxin-detoxifying agents in dairy cattle feed on natural whey starter biodiversity.

Natural whey cultures (NWC) are undefined multiple-strain bacterial starter communities that can be affected by even small changes along the entire dairy chain. We applied a multidisciplinary approach to investigate how the addition of 2 mycotoxin-detoxifying agents [sodium smectite and lignocellulose-based material (B1); leonardite and betaine (B2)] to cow diets modified the microbiota of the NWC in manufacture of a Grana-like cheese. Microbiological and flow cytometry analyses showed that the content and viability of lactic acid bacteria (LAB) and the total whey microbiota were not affected by the detoxifying agents, and Streptococcus thermophilus, Lactobacillus helveticus, and Limosilactobacillus fermentum were the dominant taxa. Random amplified polymorphic DNA-PCR fingerprinting and metagenomic analysis highlighted differences in the bacterial community of the NWC and in the relative abundance of Bacteroidetes that increased when B1 and B2 were included in the diet. Two of 6 St. thermophilus biotypes were detected only in control samples; conversely, none of the Lb. helveticus biotypes found in control samples were isolated from B1 and B2. In vitro tests showed that the 2 binders did not significantly affect the development of St. thermophilus, but they stimulated the growth of Lb. helveticus strains recovered only from B1 and B2 NWC. The addition of binders in cow feed can affect the LAB biotypes present in NWC.

Characterization of airborne viromes in cheese production plants.

AIMS: To characterize airborne virus-like particles isolated from two cheese production plants in order to reveal their complexity in terms of viral communities and microbial genes potentially mobilized by viruses. METHODS AND RESULTS: Airborne virus-like particles have been isolated from Grana Padano and Gorgonzola PDO cheese production plants and ripening cellars. A shotgun metagenomics analysis of the isolated viromes highlighted a high complexity of the viral communities both in terms of viral taxonomy and phage-host associations. Bacterial reads in each of the viromes were confirmed to be abundant and their taxonomy appeared to be associated with the environmental parameters and the technological processes that characterize the sampling area. Antibiotic resistance genes have been identified in each virome thus confirming that phages could be involved in the mobilization of antimicrobial resistances among bacterial populations. Interestingly human viruses were also identified even if the contamination source was not revealed. CONCLUSIONS: The environmental conditions, which are imposed by the technology of the dairy process, seam to shape the viral populations as a consequence of the adaptation of microbial taxa to those environments. The identification of sequences belonging to Legionella pneumophila and to the human papillomavirus, raised some considerations about the safety of cheese-ripening cellars. SIGNIFICANCE AND IMPACT OF THE STUDY: In conclusion, the analysis of the dairy airborne viromes, has revealed a high complexity of the viral communities even if the environments where the samples were collected were confined environments. Metagenomics of airborne viral population could be a promising monitoring tool for the biological characterization of dairy environments.

Setup of a rapid method to distinguish among dead, alive, and viable but not cultivable cells of Pseudomonas spp. in mozzarella cheese.

Pseudomonas spp. is the main psychrotrophic genus involved in the spoilage of raw milk and more in general of dairy products, such as mozzarella cheese. The members of this bacterial species are able to produce heat-resistant proteolytic enzymes, determining the casein hydrolysis, and as a consequence, a reduction of the shelf life and sensory quality of the products. Therefore, the spoilage activity could be attributed not only to viable, but also to viable but noncultivable (VBNC) cells. For this reason, the setup of a non-culture-based method is useful for a rapid detection of cells that are still alive, but no longer cultivable, such as VBNC cells. Here we propose a method based on DNA or RNA content (or both) to reveal the presence of dead, alive, and VBNC cells belonging to the genus Pseudomonas. The obtained results clearly indicate the limits of the classical plating count overcome by molecular detection of Pseudomonas spp. through DNA and RNA analysis, enabling us to establish the presence of different states of the cells.

Carbamoylphosphate synthetase activity is essential for the optimal growth of Streptococcus thermophilus in milk.

AIM: The aim of the study was to study the role of carbon dioxide metabolism in Streptococcus thermophilus through investigation of the phenotype of a carbamoylphosphate synthetase-negative mutant. METHODS AND RESULTS: The effect of carbon dioxide on the nutritional requirements of Strep. thermophilus DSM20617(T) and its derivative, carbamoylphosphate synthetase-negative mutant A17(DeltacarB), was investigated by cultivating the strain in a chemically defined medium under diverse gas compositions and in milk. The results obtained revealed that CO(2) depletion or carB gene inactivation determined the auxotrophy of Strep. thermophilus for l-arginine and uracil. In addition, the parent strain grew faster than the mutant, even when milk was supplemented with uracil or arginine. CONCLUSIONS: Milk growth experiments underlined that carbamoylphosphate synthetase activity was essential for the optimal growth of Strep. thermophilus in milk. SIGNIFICANCE AND IMPACT OF THE STUDY: The study of the carbon dioxide metabolism in Strep. thermophilus revealed new insights with regard to the metabolism of this species, which could be useful for the optimization of dairy fermentation processes.