This is not fully reflected in our results as we found only two Lb. helveticus DPC4571 genes, lhv_1161 and lhv_1171, that were unique to dairy and multi-niche organisms, both of which are carboxypeptidases from the M20/M25/M40 metallopeptidase
family. The role of metallopeptidases in LAB is not fully understood but they could play different roles at the physiological and technological level. These proteins could be involved in bacterial growth by supplying amino acids; for example, PepS has been shown to release phenylalanine and arginine, which are known to stimulate the growth of S. thermophilus CNRZ302 in milk. Metallopeptidases may also Crenolanib participate in the development of flavour in food products, either directly, by hydrolysing bitter peptides which are generally rich in hydrophobic amino acids and
therefore good substrates for its action, or indirectly through the liberation PF-02341066 clinical trial of aromatic amino acids which are precursors of aroma compounds identified in cheese . A broader BLAST search for validation revealed that lhv_1161 and lhv_1171 had homologues in Listeria, Staphylococcus and Bacillus species, all of which are known colonisers of dairy environments, making lhv_1161 and lhv_1171 ideal dairy LAB identifiers. Restriction/Modification Systems Restriction/modification (R/M) enzymes digest foreign DNA which has entered the cytoplasm while the host DNA remains undigested. R/M enzymes can be sub-classified into 3 groups; Type I, Type BAY 73-4506 II and Type III. Type I enzymes consist FAD of three subunits, which are responsible for modification (M), restriction (R), and specificity (S) and have been designated Hsd standing for host specificity determinant. Three type I R/M enzymes from Lb. helveticus DPC4571 are dairy organism-specific; hsdR (lhv_1031),
hsdS1 (lhv_1152) and hsdR (lhv_1978). Also, there is one dairy specific type III R/M enzyme mod (lhv_0028). A broader BLAST search confirmed that these genes only occurred in organisms capable of survival in a dairy environment with homologues in Pediococcus, Ruminococcus and Clostridia species. These 4 restriction modification genes, lhv_1031, lhv_1152, lhv_1978, lhv_0028 are therefore suitable for inclusion in our barcode as dairy specific genes. It is not clear as to why these R/M proteins are found only in the dairy organisms and not those found in a gut environment. One possibility may be that higher populations of bacteria are present in the dairy environment they may be more susceptible to phage attacks and therefore require more R/M pathways. The dairy environment usually involves the growth of the starter strains to numbers that are very high when compared to the numbers reached by similar species in other environmental niches and the same starter strains are often used repeatedly over extended periods of time.