New Insights into Metabolic Properties of Marine Bacteria Encoding Proteorhodopsins

Proteorhodopsin phototrophy was recently discovered in oceanic surface waters. In an effort to characterize uncultured proteorhodopsin-exploiting bacteria, large-insert bacterial artificial chromosome (BAC) libraries from the Mediterranean Sea and Red Sea were analyzed. Fifty-five BACs carried diverse proteorhodopsin genes, and we confirmed the function of five. We calculate that proteorhodopsin-exploiting bacteria account for 13% of microorganisms in the photic zone. We further show that some proteorhodopsin-containing bacteria possess a retinal biosynthetic pathway and a reverse sulfite reductase operon, employed by prokaryotes oxidizing sulfur compounds. Thus, these novel phototrophs are an unexpectedly large and metabolically diverse component of the marine microbial surface water

Dimethylsulfoniopropionate biosynthesis in marine bacteria and identification of the key gene in this process

Dimethylsulphoniopropionate (DMSP) is one of the Earth’s most abundant organosulphur molecules, a signalling molecule, a key nutrient for marine microorganisms, and the major precursor for gaseous dimethyl sulphide (DMS). DMS, another infochemical in signalling pathways, is important in global sulphur cycling2, and affects the Earth’s albedo, and potentially climate, via sulphate aerosol and cloud condensation nuclei production. It was thought that only eukaryotes produce significant amounts of DMSP, but here we demonstrate that many marine heterotrophic bacteria also produce DMSP, likely using the same methionine (Met) transamination pathway as macroalgae and phytoplankton10. We identify the first DMSP synthesis gene in any organism, dsyB, which encodes the key methyltransferase enzyme of this pathway and is a reliable reporter for bacterial DMSP synthesis in marine alphaproteobacteria. DMSP production and dsyB transcription are upregulated by increased salinity, nitrogen limitation and lower temperatures in our model DMSP-producing bacterium Labrenzia aggregata LZB033. With significant numbers of dsyB homologues in marine metagenomes, we propose that bacteria likely make a significant contribution to oceanic DMSP production. Furthermore, since DMSP production is not solely associated with obligate phototrophs, the process need not be confined to the photic zones of marine environments, and as such may have been underestimate

Phytoplankton responses to marine climate change – an introduction

Phytoplankton are one of the key players in the ocean and contribute approximately 50% to global primary production. They serve as the basis for marine food webs, drive chemical composition of the global atmosphere and thereby climate. Seasonal environmental changes and nutrient availability naturally influence phytoplankton species composition. Since the industrial era, anthropogenic climatic influences have increased noticeably – also within the ocean. Our changing climate, however, affects the composition of phytoplankton species composition on a long-term basis and requires the organisms to adapt to this changing environment, influencing micronutrient bioavailability and other biogeochemical parameters. At the same time, phytoplankton themselves can influence the climate with their responses to environmental changes. Due to its key role, phytoplankton has been of interest in marine sciences for quite some time and there are several methodical approaches implemented in oceanographic sciences. There are ongoing attempts to improve predictions and to close gaps in the understanding of this sensitive ecological system and its responses