Are oligotrophs not as clever as we think?

Many surface oligotrophic prokaryotes are masters at coping with a low nutrient lifestyle, but what external factors influence their ability to do so? Using 16S rRNA amplicon sequencing and biomass and production estimates, Teira et al. (2019) test how combinations of top-down grazing, bottom-up resource availability, and solar radiation control prokaryote growth and taxonomic diversity. Experiments were conducted across 10 globally distributed sites.

Results confirmed the dominance of SAR11 and cyanobacterial taxa (e.g. Prochlorococcus and Synechococcus) in low nutrient water, however when resources became less limited, their relative abundance decreased, likely because some copiotrophs (e.g. members of Rhodobacterales) could thrive with more available resources. Light exposure had a moderately low impact on growth. However, the result stating that growth was significantly reduced in 3 out of the 10 experiments contradicts this, causing confusion in their interpretation. Calculating a mean growth rate using data from all samples may have skewed the overall result perhaps causing this confusion. E.g. a Pacific site with a very deep mixed layer depth (MLD) may cause a large inhibition in growth rate. Including this low value will skew the overall mean. In the future, it may be beneficial to compare only data from sites with similar MLDs as this appears to be an important, yet uncontrolled factor.

Teira, E., Logares, R., Gutiérrez‐Barral, A., Ferrera, I., Varela, M. M., Morán, X. A. G., & Gasol, J. M. (2019). Impact of grazing, resource availability and light on prokaryotic growth and diversity in the oligotrophic surface global ocean. Environmental microbiology, 21(4), 1482-1496.