According to a two-tailed t-test, the P-value for this comparison was less than 0.001, indicating that the difference in core proteome size between the three B. anthracis isolates, and randomly chosen sets of three Bacillus isolates, was statistically significant. In fact, none of the 25 randomly-generated sets contained a larger core proteome than the set of B. anthracis isolates.

B. anthracis therefore satisfied our first criterion, since the three B. anthracis isolates had more similar protein content than randomly-chosen sets of three Bacillus isolates. B. anthracis also satisfied the second criterion, which stated that species should be distinct from other isolates of the same genus. Selleckchem Vismodegib Table 3 shows that the B. anthracis isolates contained 168 proteins not found in any other Bacillus isolate, compared to an average of just one unique protein for the 25 randomly-generated sets (P-value < 0.001). None of the 25 randomly-generated sets contained

more unique proteins than the three B. anthracis isolates. Overall, the fact that B. anthracis satisfied both criteria supports its current taxonomic classification. As another example, consider R. leguminosarum. There were Akt inhibitor 3678 proteins in its core proteome, compared to an average of 4063 for randomly selected sets of two Rhizobium isolates. This difference was not statistically significant due to the fact that only four corresponding

random groups could be created. Two of the four random Glutathione peroxidase groups–the first containing Rhizobium etli strain ATCC 51251 and R. leguminosarum strain 3841, and the second containing R. etli strain CIAT 652 and R. leguminosarum strain 3841–had larger core proteome sizes than the two R. leguminosarum isolates. The results for unique proteomes were similar, with the same two random groups having a larger unique proteome size than the two R. leguminosarum isolates. However, this apparent lack of cohesiveness can be attributed to differences in the proteome sizes of the individual isolates: the proteome of R. leguminosarum strain WSM2304 contains just 4320 proteins, compared to 5921 for the next-smallest Rhizobium isolate. As such, it might be expected that two Rhizobium isolates having proteomes much larger than that of R. leguminosarum strain WSM2304 would also have a larger core and/or unique proteome. The apparent lack of cohesiveness of Y. pestis can also be readily explained, although the reason is different than that for R. leguminosarum. There were four random groups of seven isolates each, all of which contained a mixture of Y. pestis and Yersinia pseudotuberculosis isolates, that had larger core proteomes than the seven Y. pestis isolates. All of the isolates of both Y. pestis and Y.