A red-pigmented, bacteriochlorophyll (BChl)a-producing strain, AP64^T, was isolated previously from the freshwater Swan Lake located in the western Gobi Desert. Based on its 16S rRNA gene sequence identity (96.1 %) to the type strainGemmatimonas aurantiacaT-27^T, the new isolate was tentatively classified as a member of the bacterial phylumGemmatimonadetes. Here, we report its formal description and polyphasic characterization. Strain AP64^Tgrew best on agar media under 9.8–15.2 % atmospheric oxygen. The cells were rods, dividing by symmetrical or asymmetrical binary fission. Budding structures were also observed. Its genomic DNA G+C content was 64.4 % (from the draft genome sequence). Phylogenetic analysis based on the 16S rRNA gene sequence clearly separated AP64^Tfrom related species. Its genotypic differentiation from phylogenetically close relatives was further supported by performingin silicoDNA–DNA hybridization and calculating average nucleotide identity, whereas the high percentage (67.3 %) of shared conserved proteins between strain AP64^TandGemmatimonas aurantiacaT-27^Tsupports the classification of the two strains into the same genus. Strain AP64^Tcontained C_16 : 1, C_14 : 1and C_18 : 1ω9cas predominant fatty acids. The main respiratory quinone was menaquinone 8 (MK-8). The most distinctive feature of strain AP64^Twas the presence of fully functional purple bacterial photosynthetic reaction centres. The main CO₂-fixation pathways were absent. Strain AP64^Twas capable of growth and BChl production in constant darkness. Thus, strain AP64^Tis a facultatively photoheterotrophic organism. It represents a novel species of the genusGemmatimonas, for which the nameGemmatimonasphototrophicasp. nov. is proposed. The type strain is AP64^T( = DSM 29774^T = MCCC 1K00454^T). Emended descriptions of the genusGemmatimonasandGemmatimonas aurantiacaare also provided.

Envelope‐free chloroplasts were imaged in situ by contact and tapping mode scanning force microscopy at a lateral resolution of 3–5 nm and vertical resolution of ∼0.3 nm. The images of the intact thylakoids revealed detailed structural features of their surface, including individual protein complexes over stroma, grana margin and grana‐end membrane domains. Structural and immunogold‐assisted assignment of two of these complexes, photosystem I (PS I) and ATP synthase, allowed direct determination of their surface density, which, for both, was found to be highest in grana margins. Surface rearrangements and pigment– protein complex redistribution associated with salt‐induced membrane unstacking were followed on native, hydrated specimens. Unstacking was accompanied by a substantial increase in grana diameter and, eventually, led to their merging with the stroma lamellae. Concomitantly, PS IIα effective antenna size decreased by 21% and the mean size of membrane particles increased substantially, consistent with attachment of mobile light‐harvesting complex II to PS I. The ability to image intact photosynthetic membranes at molecular resolution, as demonstrated here, opens up new vistas to investigate thylakoid structure and function.