, 2007; Zhou et al., 2009; da Miguel et al., 2010),
such methods may provide an inaccurate description of the total microbial structure in that they reveal only dominant populations, which may not necessarily Proteasome inhibitors in cancer therapy play important roles in overall community dynamics. Lacticin 3147 is a potent, two-peptide broad spectrum lantibiotic (class I bacteriocin or antimicrobial peptide) produced by Lactococcus lactis DPC3147 (Fig. 1; Ryan et al., 1996; Martin et al., 2004; Lawton et al., 2007). First isolated from an Irish kefir grain in 1996, it is perhaps one of the most extensively studied bacteriocins and has been shown to inhibit such clinically relevant pathogens as Clostridium difficile, R788 methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci (Rea et al., 2007; Piper et al., 2009). Although the microbial composition of kefir grains has been well documented (Rea et al., 1996; Ninane et al., 2007;
Zhou et al., 2009), to our knowledge, there have been no reports on the characterization of the microbiota of a kefir grain from which bacteriocin-producing strains have been isolated. In recent years, the field of microbial ecology has been revolutionized by the development and application of high-throughput DNA sequencing technologies, such as that facilitated by the 454 GS-FLX platform (Roche Diagnostics Ltd, West Sussex, UK; Keijser et al., 2008; Urich et al., 2008; McLellan et al., 2009), which allows for a more complete view of overall community composition without the bias typically associated with cloning or cultivation. Here, we use high-throughput sequencing of 16S rRNA gene amplicons to characterize the bacterial composition of the original Irish kefir from which L. lactis DPC3147 was initially isolated. The kefir grain starter used in this study was obtained from the Teagasc Food Research Centre (Fig. 1a; Teagasc, Fermoy, Ireland) kefir grain collection. The grain was cultured in sterile 10%
reconstituted skim milk at 21 °C for 24 h. The fermented Urocanase kefir milk was removed and the grain rinsed with sterile water to remove any clotted milk still adhered onto the grain surface. In order to monitor bacterial changes over the course of the kefir fermentation, kefir milk samples were enumerated for lactococci and lactobacilli; populations typically associated with the kefir community. Samples were first homogenized as 10-fold serial dilutions, further 10-fold serial dilutions were prepared and appropriate dilutions were spread plated onto M17 agar supplemented with 0.5% lactose (LM17; Difco Laboratories, Detroit, MI) for lactococci, and Lactobacillus selection agar (LBS; Difco) for lactobacilli populations. LM17 plates were incubated aerobically at 30 °C overnight and LBS plates were incubated anaerobically at 37 °C for 5 days.