ALBERT

Description: 〈p〉All known phototrophic metabolisms on Earth rely on one of three categories of energy-converting pigments: chlorophyll-〈i〉a〈/i〉 (rarely -〈i〉d〈/i〉), bacteriochlorophyll-〈i〉a〈/i〉 (rarely -〈i〉b〈/i〉), and retinal, which is the chromophore in rhodopsins. While the significance of chlorophylls in solar energy capture has been studied for decades, the contribution of retinal-based phototrophy to this process remains largely unexplored. We report the first vertical distributions of the three energy-converting pigments measured along a contrasting nutrient gradient through the Mediterranean Sea and the Atlantic Ocean. The highest rhodopsin concentrations were observed above the deep chlorophyll-〈i〉a〈/i〉 maxima, and their geographical distribution tended to be inversely related to that of chlorophyll-〈i〉a〈/i〉. We further show that proton-pumping proteorhodopsins potentially absorb as much light energy as chlorophyll-〈i〉a〈/i〉–based phototrophy and that this energy is sufficient to sustain bacterial basal metabolism. This suggests that proteorhodopsins are a major energy-transducing mechanism to harvest solar energy in the surface ocean.〈/p〉

Description: Aim To test whether within-species and among-species patterns of abundance and latitudinal range in marine bacteria resemble those found for macro-organisms, and whether these patterns differ along latitudinal clines. Location Global pelagic marine environments. Methods Taxon-specific sequence abundance and location were retrieved from the open-access V6-rRNA pyrotag sequence data base VAMPS (http://vamps.mbl.edu/), which holds a massive collection of marine bacterial community data sets from the International Census of Marine Microbes sampling effort of global ocean water masses. Data were randomly subsampled to correct for spatial bias and for differences in sampling effort. Results We show that bacterial latitudinal ranges are narrower than expected by chance. When present in both Northern and Southern hemispheres, taxa occupy restricted ranges at similar latitudes on both sides of the equator. A significant and positive relationship exists between sequence abundance and latitudinal range, although this pattern contains a large amount of variance. Abundant taxa in the tropics and in the Northern Hemisphere generally have smaller ranges than those in the Southern Hemisphere. We show that the mean latitudinal range of bacterial taxa increases with latitude, supporting the existence of a Rapoport effect in marine bacterioplankton. Finally, we show that bacterioplankton communities contain a higher proportion of abundant taxa as they approach the poles. Main conclusions Macroecological patterns such as the abundance–range relationship, in general, extend to marine bacteria. However, differences in the shape of these relationships between bacteria and macro-organisms call into question whether the processes and their relative importance in shaping global marine bacteria and macro-organism distributions are the same.