title: Identification and analysis of four candidate symbiosis genes from 'Chlorochromatium aggregatum', a highly developed bacterial symbiosis.
abstract: The consortium 'Chlorochromatium aggregatum' currently represents the most highly developed interspecific association between prokaryotes. It consists of green sulfur bacteria, so-called epibionts, which surround a central, motile, chemotrophic bacterium. Four putative symbiosis genes of the epibiont were recovered by suppression subtractive hybridization and bioinformatics approaches. These genes are transcribed constitutively and do not occur in the free-living relatives of the epibiont. The haemagglutinin-like putative gene products of open reading frames (ORFs) Cag0614 and Cag0616 are unusually large and contain repetitive regions and RGD tripeptides. Cag0616 harbours two betagamma-crystalline Greek key motifs. Cag1920 codes for a putative haemolysin whereas the gene product of Cag1919 is a putative RTX-like protein. Based on detailed analyses of Cag1919, the C-terminal amino acid sequence comprises six repetitions of the motif GGXGXD predicted to form a Ca(2+)-binding beta roll. Intact 'C. aggregatum' consortia disaggregated upon the addition of EGTA or pyrophosphate, but stayed intact in the presence of various lectine-binding sugars or proteolytic enzymes. Unlike other RTX toxins, a gene product of Cag1919 could not be detected by (45)Ca(2+) autoradiography, indicating a low abundance of the corresponding protein in the cells. The RTX-type C-terminus coded by Cag1919 exhibited a significant similarity to RTX modules of various proteobacterial proteins, suggesting that this putative symbiosis gene has been acquired via horizontal gene transfer from a proteobacterium.
authors: Bereich Mikrobiologie, Department Biologie I, Ludwig-Maximilians-Universität München, Maria-Ward-Str. 1a, München, Germany.
authors: Kajetan
authors: K
authors: Vogl
authors: Roland
authors: R
authors: Wenter
authors: Martina
authors: M
authors: Dressen
authors: Martina
authors: M
authors: Schlickenrieder
authors: Matthias
authors: M
authors: Plöscher
authors: Lutz
authors: L
authors: Eichacker
authors: Jörg
authors: J
authors: Overmann
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D019414:Chlorobi / Q000235:genetics* / Q000502:physiology; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D005798:Genes, Bacterial; D006388:Hemagglutinins / Q000235:genetics; D006460:Hemolysin Proteins / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization / Q000379:methods; D016366:Open Reading Frames; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012091:Repetitive Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006388:Hemagglutinins; D006460:Hemolysin Proteins