We will use samples of ultramafic groundwaters collected in parallel on 0.1 and 0.2 µm filters from the Coast Range Ophiolite Microbiological Observatory (CROMO) site in northern California, USA and the Cabeço de Vide site to test the hypotheses that A) microbial populations <0.2 µm in size contribute to the natural microbial diversity of ultrabasic groundwaters, and B) a significant portion of the microbial diversity described using physical lysis methods is derived from recalcitrant bacterial endospores. We will compare the taxonomic compositions of community DNA extract by gentle (chemical) and rigorous (physical) lysis approaches. These studies will be conducted in concert with the quantification of spore abundances using differential centrifugation and light microscopy, and through analysis of glass fiber filters and determination of the spore protein dipicolinic acid.