Distribution and Growth of Aerobic Anoxygenic Phototrophs in the Mediterranean Sea

9 pages, 6 figures, 2 tablesThe distribution of aerobic anoxygenic phototrophs (AAPs) was surveyed in various regions of the Mediterranean Sea in spring and summer. These phototrophic bacteria were present within the euphotic layer at all sampled stations. The AAP abundances increased with increasing trophic status ranging from 2.5 × 103 cells per ml in oligotrophic Eastern Mediterranean up to 90 × 103 cells per ml in the Bay of Villefranche. Aerobic anoxygenic phototrophs made up on average 1–4% of total prokaryotes in low nutrient areas, whereas in coastal and more productive stations these organisms represented 3–11% of total prokaryotes. Diel bacteriochlorophyll a decay measurements showed that AAP community in the Western Mediterranean grew rapidly, at rates from 1.13 to 1.42 day−1. The lower AAP abundances registered in the most oligotrophic waters suggest that they are relatively poor competitors under nutrient limiting conditions. Instead, AAPs appear to be metabolically active organisms, which thrive better in more eutrophic environments providing the necessary substrates to maintain high growth ratesThis research was supported by AV Cˇ R project M200200903, project Algatech (CZ.1.05/2.1.00/03.0110) and the Inst. research concepts MSM6007665808 and AV0Z50200510. The June 2007 cruise in the eastern Mediterranean Sea was carried out under the framework of the Italian project VECTOR. The Modivus cruise was funded by Spanish project CTM2005-04795/MAR to J.M. GasolPeer reviewe

Light enhances the growth rates of natural populations of aerobic anoxygenic phototrophic bacteria

3 pages, 2 figures, supplementary information https://dx.doi.org/10.1038/ismej.2017.79Aerobic anoxygenic phototrophic (AAP) bacteria are microorganisms that can harvest light energy using bacteriochlorophyll a to supplement their predominantly organotrophic metabolism. Growth enhancement by light has repeatedly been demonstrated in laboratory experiments with AAP isolates. However, the ecological advantage of light utilization is unclear, as it has never been proven in the natural environment. Here, we conducted manipulation experiments in the NW Mediterranean and found that AAP bacteria display high growth rates which are controlled to a large extent by intense grazing pressure and phosphorous availability. Foremost, we found that, contrarily to the bulk bacterioplakton, AAP bacteria display higher growth rates when incubated under light-dark cycles than in complete darkness. These results represent the first direct evidence that natural populations of marine AAP bacteria can be stimulated by lightThis work was supported by grant REMEI (CTM2015-70340-R) from the Spanish Ministry of Economy, Industry and Competitivity. MK was supported by the GA ČR project 13-11281S and the MŠMT project Algatech PlusPeer Reviewe