Measuring ribosome decay and production to determine taxon-specific microbial mortality rates

Association for the Sciences of Limnology and Oceanography (ASLO) Summer meeting, Water connects!, 10-15 June 2018, Victoria, Canada
Microbes comprise >90% of the biomass in the world's oceans, drive biogeochemical cycles, and have turnover rates ranging from hours to days. Despite the central role of microbes in marine systems, there is no robust way to evaluate taxon-specific mortality. Previously, we reported that there are millions of free-ribosomes per mL of seawater that are released by cell lysis, and that these can be used to estimate taxon-specific cell lysis. Here, ribosome decay and production rates were used to estimate taxon-specific microbial mortality in surface waters of the Red Sea. Free-ribosome production, indicative of cell lysis, was detected in 953 out of 1308 prokaryotic taxa after incubations with or without mitomycin C. In 261 taxa (~27%), ribosome production only occurred with mitomycin C addition, suggesting that lysis was caused by prophage induction. Overall, 60 different dynamic patterns of free-ribosomes and cells were detected across five time points in the experiment. Using the rate of ribosome production, and ribosome copy number per cell, the mortality rate of prokaryotes was estimated to average 1.3±0.64 d-1 in the controls and 2.47±0.89 d-1 in Mitomycin C treatments, and varied among taxa and treatments. Some taxa had high rates of mortality, including the genera Acinetobacter, AEGEAN-169 marine group, Phyllobacterium, Microbacterium, Halomonas and Thalassospira. Our results show high-mortality-rates are coupled to high growth rates and high relative-abundances, suggesting that r-selected have higher lysis rates. The ability to estimate taxon-specific mortality rate as the result of cell lysis adds an important tool in our quest to explain the distribution, abundance and roles of specific microbial taxa in nature