All authors read and approved the final manuscript.”
“Background Aerobic anoxygenic photoheterotrophic bacteria use light as additional energy source for mixotrophic growth and play a significant

role in the microbial ecology of marine environments [1, learn more 2]. Members of this physiological group belonging to the Alphaproteobacteria have been intensively studied (for review see e.g.[3, 4]), but so far little is known on the phenotypic diversity of representatives belonging to the Gammaproteobacteria. The existence of aerobic anoxygenic photoheterotrophic gammaproteobacteria in marine environments was first postulated in a study by Béjà et al. [5], who could identify photosynthesis genes in partial genome sequences of gammaproteobacteria retrieved from seawater off the coast of California (USA). A few years later the two marine isolates HTCC2080 and KT71T were independently identified as aerobic anoxygenic photoheterotrophic gammaproteobacteria by proteomic analyses [6] and genome sequencing [7], respectively. Strain KT71T was subsequently characterized in detail and described as Congregibacter litoralis (C. litoralis) by Spring click here et al. [8], thereby representing the first photoheterotrophic bacterium of this group with a validly

published name. Phylogenetically, C. litoralis is affiliated to a large coherent cluster of 16S rRNA gene sequences, which were mainly retrieved by cultivation-independent aminophylline methods from marine habitats around the world. This sequence cluster was recognized as a distinct lineage within the class Gammaproteobacteria and designated as OM60 [9, 10] or NOR5 clade [11]. Metabolic active bacteria representing

this clade could be detected in numerous environmental selleck inhibitor samples by using fluorescence in situ hybridization experiments [12, 13]. Based on these findings it is assumed that the OM60/NOR5 clade of Gammaproteobacteria is of significant ecological importance due to its widespread occurrence in the euphotic zone of saline ecosystems and high abundance especially in coastal waters [6, 13, 14]. A phylogenetic lineage closely related to the OM60/NOR5 cluster was originally defined by a 16S rRNA gene sequence retrieved from deep sea sediment and designated BD1-7 [13]. In recent years reports about the isolation of additional strains belonging to the OM60/NOR5 group have accumulated. Some of these strains were described as mixotrophs containing photosynthetic pigments [6, 15] or proteorhodopsin (PR) [16]. In contrast, no photosynthetic pigments were reported in members of the genus Haliea[17–19] or Halioglobus[20].