Comparison of Bacterial Diversity in Azorean and Hawai'ian Lava Cave Microbial Mats

Abstract

Worldwide, lava caves host colorful microbial mats. However, little is known about the diversity of these microorganisms, or what role they may play in the subsurface ecosystem. White and yellow microbial mats were collected from four lava caves each on the Azorean island of Terceira and the Big Island of Hawai'i, to compare the bacterial diversity found in lava caves from two widely separated archipelagos in two different oceans at different latitudes. Scanning electron microscopy of mat samples showed striking similarities between Terceira and Hawai'ian microbial morphologies. 16S rRNA gene clone libraries were constructed to determine the diversity within these lava caves. Fifteen bacterial phyla were found across the samples, with more Actinobacteria clones in Hawai'ian communities and greater numbers of Acidobacteria clones in Terceira communities. Bacterial diversity in the subsurface was correlated with a set of factors. Geographical location was the major contributor to differences in community composition (at the OTU level), together with differences in the amounts of organic carbon, nitrogen and copper available in the lava rock that forms the cave. These results reveal, for the first time, the similarity among the extensive bacterial diversity found in lava caves in two geographically separate locations and contribute to the current debate on the nature of microbial biogeography.

Keywords:

• Azores
• Hawai'i
• lava cave
• microbial communities

Acknowledgments

We would like to thank Dr. P. Boston, D. Medville, H. Medville, E. Davis, M. Warner, L. Fleming, and D. and B. Coons for assistance with field work in Hawai'i and A. Dapkevicius, A.R. Varela, F. Pereira, P. Cardoso, C. Gaspar and A.F. Rodrigues with field work in Terceira. For permits and access to the lava caves we thank the Cave Conservancy of Hawai'i, Hawai'i Volcanoes National Park, Os Montanheiros, and the landowners. We thank Frank Haworth, Joaquín Hortal, Andrea Porras-Alfaro, Cristina Riquelme Gabriel and Robert Sinsabaugh for conversations and comments on previous drafts that greatly improved this manuscript.