title: Experimental Warming Decreases the Average Size and Nucleic Acid Content of Marine Bacterial Communities.
abstract: Organism size reduction with increasing temperature has been suggested as a universal response to global warming. Since genome size is usually correlated to cell size, reduction of genome size in unicells could be a parallel outcome of warming at ecological and evolutionary time scales. In this study, the short-term response of cell size and nucleic acid content of coastal marine prokaryotic communities to temperature was studied over a full annual cycle at a NE Atlantic temperate site. We used flow cytometry and experimental warming incubations, spanning a 6°C range, to analyze the hypothesized reduction with temperature in the size of the widespread flow cytometric bacterial groups of high and low nucleic acid content (HNA and LNA bacteria, respectively). Our results showed decreases in size in response to experimental warming, which were more marked in 0.8 μm pre-filtered treatment rather than in the whole community treatment, thus excluding the role of protistan grazers in our findings. Interestingly, a significant effect of temperature on reducing the average nucleic acid content (NAC) of prokaryotic cells in the communities was also observed. Cell size and nucleic acid decrease with temperature were correlated, showing a common mean decrease of 0.4% per °C. The usually larger HNA bacteria consistently showed a greater reduction in cell and NAC compared with their LNA counterparts, especially during the spring phytoplankton bloom period associated to maximum bacterial growth rates in response to nutrient availability. Our results show that the already smallest planktonic microbes, yet with key roles in global biogeochemical cycling, are likely undergoing important structural shrinkage in response to rising temperatures.
authors.affiliation: Plankton Ecology and Pelagic Ecosystem Dynamics, Centro Oceanográfico de Gijón/Xixón, Instituto Español de Oceanografía Gijón/Xixón, Spain.
authors.forename: Tamara M
authors.initials: TM
authors.lastname: Huete-Stauffer
authors.affiliation: Plankton Ecology and Pelagic Ecosystem Dynamics, Centro Oceanográfico de Gijón/Xixón, Instituto Español de Oceanografía Gijón/Xixón, Spain.
authors.forename: Nestor
authors.initials: N
authors.lastname: Arandia-Gorostidi
authors.affiliation: Plankton Ecology and Pelagic Ecosystem Dynamics, Centro Oceanográfico de Gijón/Xixón, Instituto Español de OceanografíaGijón/Xixón, Spain; Marine Research Division, AZTISukarrieta, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Alonso-Sáez
authors.affiliation: Plankton Ecology and Pelagic Ecosystem Dynamics, Centro Oceanográfico de Gijón/Xixón, Instituto Español de OceanografíaGijón/Xixón, Spain; Division of Biological and Environmental Sciences and Engineering, Red Sea Research Center, King Abdullah University of Science and TechnologyThuwal, Saudi Arabia.
authors.forename: Xosé Anxelu G
authors.initials: XA
authors.lastname: Morán
keywords: coastal ocean; flow cytometry; marine bacteria; nucleic acids; size; temperature-size rule