although it is not possible to pinpoint the time frame for that growth. Comparing the hydrogen isotope ratios from water from DPG to a model for all known media, Kreuzer-Martin and colleagues concluded that it was highly unlikely that water from DPG was used to prepare the sample; however, it was not possible to identify the location where the spores were prepared.
Finding 4.6: The flask designated RMR-1029 was not the immediate, most proximate source of the letter material. If the letter material did in fact derive from RMR-1029, then one or more separate growth steps, using seed material from RMR-1029 followed by purification, would have been necessary. Furthermore, the evidentiary material in the New York letters had physical properties that were distinct from those of the material in the Washington, D.C. letters.
SEM-EDX measurements showed no silicon in the coats of spores taken directly from RMR-1029, whereas the majority of spores analyzed from the New York Post, Daschle, and Leahy letter materials contained silicon in the coat. Based on recent studies of the mechanism of silicon incorporation, silicon could have been incorporated in the coats of the letter spores only if spores from RMR-1029 were subjected to one or more subsequent growth steps. Another observation consistent with a separate growth step was the detection of B. subtilis in the New York Post and Brokaw letter material but not in RMR-1029 (discussed in Chapter 5). The detection of meglumine and diatrizoate in RMR-1029 but not in the Leahy and New York Post samples also is consistent with this finding; however, it is not conclusive because it might have been possible to rinse these impurities away without requiring later growth. Some of these findings, as well as others, indicate that the New York letter materials were prepared separately from the materials in the Washington, D.C., letters. The presence of B. subtilis in the New York but not the Washington letter materials and the different physical properties of the materials indicate that the two sets of letter materials were prepared separately.