May 21, 2014
Luke McKay, University of North Carolina, Chapel Hill
Approaching the high temperature boundary for life in the hydrothermally altered sediments of Guaymas Basin
My research focuses on microbial community structure in the hydrothermally-altered sediments of Guaymas Basin at 2000m water depth in the Sea of Cortez. The thermal range of shallow Guaymas sediments is extreme; on one occasion temperatures increased from 3°C at the sediment-water interface to 200°C in just 45cm. Beyond 80°C and 100°C the isotopic signatures of the anaerobic oxidation of methane (AOM) and organic matter remineralization (OMR) could not be traced and may represent upper thermal constraints for these microbial processes.
Temperature logging probes revealed that the shallowest sediments experienced extreme thermal fluctuations, which sometimes varied by 25°C in as little as a day. Viable microbial life, as indicated by reverse-transcribed 16S rRNA, was detected in sediments with an eight day thermal range of 77°C to 100°C. 454-pyrosequencing recovery of reverse-transcribed 16S rRNA from cool and hot layers of high temperature cores revealed that putative methane cycling archaea and sulfur cycling bacteria were dominant members of the microbial community.
In particular, ANME archaea were very common but distinct cores yielded diverse sequence assemblages, including ANME-1 Guaymas, ANME-2c, and ANME-2d / GoM Arc-1 / Methanoperedenaceae. Dominant bacterial groups were Thermodesulfobacteria within the family Thermodesulfobacteriaceae, Epsilonproteobacteria within the family Helicobacteriaceae, and close relatives of the deltaproteobacterium Desulfocapsa exigens. Co-occurrence of OTUs across the four hottest sediment layers suggests that ANME-1 Guaymas and an uncultured representative of a deeply branching MCG subgroup are the most probable archaeal hyperthermophiles, and members of the Thermodesulfobacteriaceae family are likely bacterial hyperthermophiles.
Luke McKay received his bachelor of science in biology from the University of Alabama at Birmingham where he studied environmental toxicology and transcriptional regulation in mosquitofish from local streams and rivers. His interest in the origins and limits of life led him to Andreas Teske’s lab at the University of North Carolina at Chapel Hill where he pursued a Masters degree in marine sciences by studying deep-sea microbial mats that colonize active hydrothermal seeps in Guaymas Basin in the Gulf of California. After completing his Masters, he started his PhD in the same lab to investigate patterns in microbial biogeography in high temperature sediments. Luke’s most recent work focuses on the upper thermal limits of uncultured life in hydrothermally altered mud. Luke became a C-DEBI graduate fellow in 2012 and successfully defended his PhD the week before this broadcast.