August 24, 11am PT:Karen G. Lloyd (University of Tennessee) leads the next C-DEBI Professional Development Webinar on “How to Negotiate in Academia,” covering why negotiation is essential, tips for how to do so successfully and what to expect from post-doc and assistant professorship job negotiations.
September 7, 12:30pm PT: Dr. Gustavo Ramírez (University of Rhode Island) will give the next Networked Speaker Series Seminar on “Microbial Neter-Khertet: Life and death post-entombment.” Abstract: Deep ocean sediment is a diffusion-limited environment where microbial inhabitants persist despite extreme temporal, physical and nutritional isolation from the ocean above. Burial time increases with sediment depth and, unsurprisingly, community richness, diversity, cell abundance and metabolic activity drop significantly with sediment age, implying both a steep selection curve and concomitant mass death. The extent to which benthic necromass (fragments of cadaverous cells), specifically extracellular DNA, a molecular fossil, may affect environmental sequencing surveys is a critical question that has received little attention. Reasons for this neglect are i) DNA is generally believed to have a short molecular half-life and ii) extracellular DNA represents dissolved C, N and P which should be readily metabolized by active microbes. The scarcity of methods for assessing microbial viability in complex environmental samples further confounds this issue. I interrogated Arctic and Pacific sediments for the presence of detrital DNA using Propidium Monoazide, a photo-active DNA intercalating dye that cannot penetrate intact prokaryotic membranes. This approach employs membrane integrity, a prerequisite for chemiosmotic potential and ATP production, as a viability metric. I detected statistically significant extracellular 16S rRNA gene loads in shallow sediment horizons, but not deep horizons. Measures of Alpha- and Beta-diversity for intra-and total-16rRNA gene pools are somewhat variable. Diversity trends are generally similar for both DNA pools, but noisier at shallow depths.