Award: OCE-1536776

Intellectual Merit: This project compared the types of microbes present in bottom water and surficial sediments of two of the deepest locations on Earth. These were the Kermadec Trench located off the north coast of New Zealand, and the Mariana Trench, mostly located within the United States Mariana Trench Marine National Monument, but also occupying a portion of the territorial waters of Micronesia. Trenches can be considered to be upside down mountain ranges. These two trench systems are separately from one another by ~6,000 kilometers. In this grant we compared the microbes in these two trenches using highly quantitative marker gene DNA sequencing and comparative genomics. In addition, the microbes were also examined in terms of their activity and growth characteristics. The results indicated that deep-sea microbial populations consist of a mixture of taxa descending from shallow waters above and taxa adapted to life at great depth, including extremes of high pressure and low temperature. Seawater depth, trench of collection, size fraction, sediment depth, and organic levels were all found to correlate with distinctive types of microorganisms (Figure 2). Long-term incubation of trench sediments at the pressures and temperatures of their natural environment dramatically changed the composition of the microbial community to one containing a majority of previously documented and cultured high pressure-adapted microbes. Seventy-nine draft genome sequences from trench microbes were obtained. Analyses of these genomes indicated that many of the same species are shared between these two widely separated trenches, but that trench-specific strains also exist. This work demonstrated that microbes in deep trenches can be shared across great geographic distances, presumably moving along ocean currents. Broader Impacts: A detailed description was provided of a free-falling and ascending instrument coupled with a pressure-retaining seawater sampling system. This instrument is of value to the deep-sea science community. The grant provided support for one PhD student, the training of 7 undergraduates (4 serving as coauthors on publications, two in PhD programs, one in a MD-PhD program), and provided the opportunity to host 5 visiting PhD students (Oregon State University, Princeton University, IIT, India, University of Aberdeen, and Southern University of Denmark). It was associated with numerous BCO-DMO datasets and 16 international presentations. Outreach included presentations to >60 middle/high school girls, a microbial ecology booth at the Birch Aquarium, a lecture to 160 K-12 teachers, audio/written interviews for "Science News for Students", numerous undergraduate and graduate lectures by the PI and PhD student, and service as instructor (PI) and TA (PhD student) in the NSF Polar Biology Training Course in Antarctica. Last Modified: 12/16/2019 Submitted by: Douglas H Bartlett