Analysis of the completely determined genomes of the plant-derived Acholeplasma brassicae strain O502 and A. palmae strain J233 revealed that the circular chromosomes are 1,877,792 and 1,554,229 bp in size, have a G + C content of 36 and 29%, and encode 1,690 and 1,439 proteins, respectively. Comparative analysis of these sequences and previously published genomes of A. laidlawii strain PG-8, 'Candidatus Phytoplasma asteris' strains, 'Ca. P. australiense' and 'Ca. P. mali' show a limited shared basic genetic repertoire. The acholeplasma genomes are characterized by a low number of rearrangements, duplication and integration events. Exceptions are the unusual duplication of rRNA operons in A. brassicae and an independently introduced second gene for a single-stranded binding protein in both genera. In contrast to phytoplasmas, the acholeplasma genomes differ by encoding the cell division protein FtsZ, a wide variety of ABC transporters, the F0F1 ATP synthase, the Rnf-complex, SecG of the Sec-dependent secretion system, a richly equipped repertoire for carbohydrate metabolism, fatty acid, isoprenoid and partial amino acid metabolism. Conserved metabolic proteins encoded in phytoplasma genomes such as the malate dehydrogenase SfcA, several transporters and proteins involved in host-interaction, and virulence-associated effectors were not predicted for the acholeplasmas.
Among the dominant deltaproteobacterial sulfate-reducing bacteria (SRB), members of the genus Desulfobacula are not only present in (hydrocarbon-rich) marine sediments, but occur also frequently in the anoxic water bodies encountered in marine upwelling areas. Here, we present the 5.2 Mbp genome of Desulfobacula toluolica Tol2, which is the first of an aromatic compound-degrading, marine SRB. The genome has apparently been shaped by viral attacks (e.g. CRISPRs) and its high plasticity is reflected by 163 detected genes related to transposases and integrases, a total of 494 paralogous genes and 24 group II introns. Prediction of the catabolic network of strain Tol2 was refined by differential proteome and metabolite analysis of substrate-adapted cells. Toluene and p-cresol are degraded by separate suites of specific enzymes for initial arylsuccinate formation via addition to fumarate (p-cresol-specific enzyme HbsA represents a new phylogenetic branch) as well as for subsequent modified beta-oxidation of arylsuccinates to the central intermediate benzoyl-CoA. Proteogenomic evidence suggests specific electron transfer (EtfAB) and membrane proteins to channel electrons from dehydrogenation of both arylsuccinates directly to the membrane redox pool. In contrast to the known anaerobic degradation pathways in other bacteria, strain Tol2 deaminates phenylalanine non-oxidatively to cinnamate by phenylalanine ammonia-lyase and subsequently forms phenylacetate (both metabolites identified in (13) C-labelling experiments). Benzoate degradation involves CoA activation, reductive dearomatization by a class II benzoyl-CoA reductase and hydrolytic ring cleavage as found in the obligate anaerobe Geobacter metallireducens GS-15. The catabolic sub-proteomes displayed high substrate specificity, reflecting the genomically predicted complex and fine-tuned regulatory network of strain Tol2. Despite the genetic equipment for a TCA cycle, proteomic evidence supports complete oxidation of acetyl-CoA to CO2 via the Wood-Ljungdahl pathway. Strain Tol2 possesses transmembrane redox complexes similar to that of other Desulfobacteraceae members. The multiple heterodisulfide reductase-like proteins (more than described for Desulfobacterium autotrophicum HRM2) may constitute a multifaceted cytoplasmic electron transfer network.
Microorganisms can degrade saturated hydrocarbons (alkanes) not only under oxic but also under anoxic conditions. Three denitrifying isolates (strains HxN1, OcN1, HdN1) able to grow under anoxic conditions by coupling alkane oxidation to CO(2) with NO(3) (-) reduction to N(2) were compared with respect to their alkane metabolism. Strains HxN1 and OcN1, which are both Betaproteobacteria, utilized n-alkanes from C(6) to C(8) and C(8) to C(12) respectively. Both activate alkanes anaerobically in a fumarate-dependent reaction yielding alkylsuccinates, as suggested by present and previous metabolite and gene analyses. However, strain HdN1 was unique in several respects. It belongs to the Gammaproteobacteria and was more versatile towards alkanes, utilizing the range from C(6) to C(30). Neither analysis of metabolites nor analysis of genes in the complete genome sequence of strain HdN1 hinted at fumarate-dependent alkane activation. Moreover, whereas strains HxN1 and OcN1 grew with alkanes and NO(3) (-), NO(2) (-) or N(2)O added to the medium, strain HdN1 oxidized alkanes only with NO(3) (-) or NO(2) (-) but not with added N(2)O; but N(2)O was readily used for growth with long-chain alcohols or fatty acids. Results suggest that NO(2) (-) or a subsequently formed nitrogen compound other than N(2)O is needed for alkane activation in strain HdN1. From an energetic point of view, nitrogen-oxygen species are generally rather strong oxidants. They may enable enzymatic mechanisms that are not possible under conditions of sulfate reduction or methanogenesis and thus allow a special mode of alkane activation.
Dinoroseobacter shibae DFL12(T), a member of the globally important marine Roseobacter clade, comprises symbionts of cosmopolitan marine microalgae, including toxic dinoflagellates. Its annotated 4 417 868 bp genome sequence revealed a possible advantage of this symbiosis for the algal host. D. shibae DFL12(T) is able to synthesize the vitamins B(1) and B(12) for which its host is auxotrophic. Two pathways for the de novo synthesis of vitamin B(12) are present, one requiring oxygen and the other an oxygen-independent pathway. The de novo synthesis of vitamin B(12) was confirmed to be functional, and D. shibae DFL12(T) was shown to provide the growth-limiting vitamins B(1) and B(12) to its dinoflagellate host. The Roseobacter clade has been considered to comprise obligate aerobic bacteria. However, D. shibae DFL12(T) is able to grow anaerobically using the alternative electron acceptors nitrate and dimethylsulfoxide; it has the arginine deiminase survival fermentation pathway and a complex oxygen-dependent Fnr (fumarate and nitrate reduction) regulon. Many of these traits are shared with other members of the Roseobacter clade. D. shibae DFL12(T) has five plasmids, showing examples for vertical recruitment of chromosomal genes (thiC) and horizontal gene transfer (cox genes, gene cluster of 47 kb) possibly by conjugation (vir gene cluster). The long-range (80%) synteny between two sister plasmids provides insights into the emergence of novel plasmids. D. shibae DFL12(T) shows the most complex viral defense system of all Rhodobacterales sequenced to date.
Sulfate-reducing bacteria (SRB) belonging to the metabolically versatile Desulfobacteriaceae are abundant in marine sediments and contribute to the global carbon cycle by complete oxidation of organic compounds. Desulfobacterium autotrophicum HRM2 is the first member of this ecophysiologically important group with a now available genome sequence. With 5.6 megabasepairs (Mbp) the genome of Db. autotrophicum HRM2 is about 2 Mbp larger than the sequenced genomes of other sulfate reducers (SRB). A high number of genome plasticity elements (> 100 transposon-related genes), several regions of GC discontinuity and a high number of repetitive elements (132 paralogous genes Mbp(-1)) point to a different genome evolution when comparing with Desulfovibrio spp. The metabolic versatility of Db. autotrophicum HRM2 is reflected in the presence of genes for the degradation of a variety of organic compounds including long-chain fatty acids and for the Wood-Ljungdahl pathway, which enables the organism to completely oxidize acetyl-CoA to CO(2) but also to grow chemolithoautotrophically. The presence of more than 250 proteins of the sensory/regulatory protein families should enable Db. autotrophicum HRM2 to efficiently adapt to changing environmental conditions. Genes encoding periplasmic or cytoplasmic hydrogenases and formate dehydrogenases have been detected as well as genes for the transmembrane TpII-c(3), Hme and Rnf complexes. Genes for subunits A, B, C and D as well as for the proposed novel subunits L and F of the heterodisulfide reductases are present. This enzyme is involved in energy conservation in methanoarchaea and it is speculated that it exhibits a similar function in the process of dissimilatory sulfate reduction in Db. autotrophicum HRM2.
Recent research on microbial degradation of aromatic and other refractory compounds in anoxic waters and soils has revealed that nitrate-reducing bacteria belonging to the Betaproteobacteria contribute substantially to this process. Here we present the first complete genome of a metabolically versatile representative, strain EbN1, which metabolizes various aromatic compounds, including hydrocarbons. A circular chromosome (4.3 Mb) and two plasmids (0.21 and 0.22 Mb) encode 4603 predicted proteins. Ten anaerobic and four aerobic aromatic degradation pathways were recognized, with the encoding genes mostly forming clusters. The presence of paralogous gene clusters (e.g., for anaerobic phenylacetate oxidation), high sequence similarities to orthologs from other strains (e.g., for anaerobic phenol metabolism) and frequent mobile genetic elements (e.g., more than 200 genes for transposases) suggest high genome plasticity and extensive lateral gene transfer during metabolic evolution of strain EbN1. Metabolic versatility is also reflected by the presence of multiple respiratory complexes. A large number of regulators, including more than 30 two-component and several FNR-type regulators, indicate a finely tuned regulatory network able to respond to the fluctuating availability of organic substrates and electron acceptors in the environment. The absence of genes required for nitrogen fixation and specific interaction with plants separates strain EbN1 ecophysiologically from the closely related nitrogen-fixing plant symbionts of the Azoarcus cluster. Supplementary material on sequence and annotation are provided at the Web page http://www.micro-genomes.mpg.de/ebn1/.
Desulfotalea psychrophila is a marine sulfate-reducing delta-proteobacterium that is able to grow at in situ temperatures below 0 degrees C. As abundant members of the microbial community in permanently cold marine sediments, D. psychrophila-like bacteria contribute to the global cycles of carbon and sulfur. Here, we describe the genome sequence of D. psychrophila strain LSv54, which consists of a 3 523 383 bp circular chromosome with 3118 predicted genes and two plasmids of 121 586 bp and 14 663 bp. Analysis of the genome gave insight into the metabolic properties of the organism, e.g. the presence of TRAP-T systems as a major route for the uptake of C(4)-dicarboxylates, the unexpected presence of genes from the TCA cycle, a TAT secretion system, the lack of a beta-oxidation complex and typical Desulfovibrio cytochromes, such as c(553), c(3) and ncc. D. psychrophila encodes more than 30 two-component regulatory systems, including a new Ntr subcluster of hybrid kinases, nine putative cold shock proteins and nine potentially cold shock-inducible proteins. A comparison of D. psychrophila's genome features with those of the only other published genome from a sulfate reducer, the hyperthermophilic archaeon Archaeoglobus fulgidus, revealed many striking differences, but only a few shared features.
Pirellula sp. strain 1 ("Rhodopirellula baltica") is a marine representative of the globally distributed and environmentally important bacterial order Planctomycetales. Here we report the complete genome sequence of a member of this independent phylum. With 7.145 megabases, Pirellula sp. strain 1 has the largest circular bacterial genome sequenced so far. The presence of all genes required for heterolactic acid fermentation, key genes for the interconversion of C1 compounds, and 110 sulfatases were unexpected for this aerobic heterotrophic isolate. Although Pirellula sp. strain 1 has a proteinaceous cell wall, remnants of genes for peptidoglycan synthesis were found. Genes for lipid A biosynthesis and homologues to the flagellar L- and P-ring protein indicate a former Gram-negative type of cell wall. Phylogenetic analysis of all relevant markers clearly affiliates the Planctomycetales to the domain Bacteria as a distinct phylum, but a deepest branching is not supported by our analyses.
