Candidate partitioning genes (parA and parB) for the linear chromosome of Streptomyces coelicolor were identified by DNA sequencing in a series of seven genes located between rnpA and trxA near the chromosomal replication origin. The most likely translation start point of parB overlapped the parA stop codon, suggestive of coregulation, and transcription analysis suggested that the two genes formed an operon. Deletion of part of parB had no effect on the growth or appearance of colonies but caused a deficiency in DNA partitioning during the multiple septation events involved in converting aerial hyphae into long chains of spores. At least 13% of spore compartments failed to inherit the normal DNA allocation. The same phenotype was obtained with a deletion removing a segment of DNA from both parA and parB. Reinforcing the idea of a special role for the par locus during sporulation, the stronger of two parAB promoters was greatly upregulated at about the time when sporulation septation was maximal in colonies. Three copies of a 14-bp inverted repeat (GTTTCACGT GAAAC) were found in or near the parAB genes, and at least 12 more identical copies were identified within 100 kb of oriC from the growing genome sequence database. Only one perfect copy of the 14-bp sequence was present in approximately 5 Mb of sequence available from the rest of the genome. The 14-bp sequence was similar to sequences identified as binding sites for Spo0J, a ParB homologue from Bacillus subtilis believed to be important for DNA partitioning

This complete and fully assembled genome sequence of Mycoplasma bovis type strain PG45 is the first available for this species and offers a framework for comparison with additional pathogenic isolates. The single circular chromosome of 1,003,404 bp reveals multiple gene sets and mechanisms involved in variable expression of surface antigens and the incursion of numerous and assorted mobile elements, despite its reduced size.Mycoplasma bovis is a major bacterial pathogen causing widespread respiratory disease, mastitis, and arthritis in cattle (1,5). A member of the wall-less Mollicutes class, it displays marked genome reduction and a parasitic lifestyle lacking key metabolic pathways. It is refractory to several classes of antibiotics, and bacterins for immunological control need continued improvement. Adaptive variation through high-frequency phase variation of surface lipoproteins (LPs) is known to occur through site-specific recombination among the family of vsp genes (8, 9). Horizontal gene transfer (HGT) of some gene sets (13), numerous classes of insertion-like sequences (IS elements) (7), and integrative conjugative elements (ICE) (10) are reported in M. bovis or its close phylogenetic relative M. agalactiae, a pathogenic species infecting caprine hosts. Complete sequencing and assembly of the M. bovis genome were pursued to better reveal its content and dynamics relevant to disease control measures. In order to minimize rearrangements or mutational heterogeneity in the genome sample, template DNA was prepared from an axenic culture propagated from a single colony isolate (MU clone A2, phenotype VspO ON; available under proper regulatory controls). The genome, comprising a single circular chromosome, was sequenced to closure using the Sanger random shotgun method (3), yielding approximately 8-fold sequence coverage.The genome has a 29.3% GϩC content, contains 826 open reading frames (ORFs; including 61 pseudogenes) with an 89% coding density, and has limited sets of 6 rRNA and 34 tRNA genes, characteristic of Mollicutes. A large set of 54 IS elements (comprising seven distinct categories) (7) is scattered throughout the chromosome. Two ICE occur. ICEB-1 (23,271 bp, 18 ORFs) is a counterpart to ICEA, an element similarly positioned in the highly syntenous M. agalactiae PG2 genome (11), thereby suggesting that integration occurred in a common ancestor prior to speciation. ICEB-2 (37,408 bp, 33 ORFs) is inserted into an IS element that is implicated in the inversion of a 483-kb region of the M. bovis PG45 chromosome, relative to M. agalactiae PG2. The potential for genome plasticity among strains of M. bovis is underscored by these features.The predicted LP surface proteome of M. bovis type strain PG45 was determined using established algorithms (2, 6) and an extended search pattern, {DERK}(6)- [LIVMFWSTAG](2)-[LIVMFYSTAGCQ]-[AGSTKRQ]-C, to include atypical residues (underlined) at the Ϫ1 position of the lipobox, previously demonstrated in this lineage of Mollicutes (4, 9). Of 96 predicted LPs, 40 contain at...

There is a worldwide problem of disease caused by Mycoplasma (M.) bovis in cattle; it has a significant detrimental economic and animal welfare impact on cattle rearing. Infection can manifest as a plethora of clinical signs including mastitis, pneumonia, arthritis, keratoconjunctivitis, otitis media and genital disorders that may result in infertility and abortion. Current diagnosis and control information are reviewed and analysed to identify gaps in knowledge of the causative organism in respect of the disease pathology, diagnosis and control methods. The main considerations are as follows: no vaccines are commercially available; antimicrobial resistance is increasing; diagnostic and antimicrobial sensitivity testing needs to be improved; and a pen-side test would facilitate more rapid diagnosis and implementation of treatment with antimicrobials. More data on host susceptibility, stress factors, immune response and infectious dose levels are required. The impact of asymptomatic carriers, M. bovis survival in the environment and the role of wildlife in transmitting the disease also needs investigation. To facilitate development of vaccines, further analysis of more M. bovis genomes, its pathogenic mechanisms, including variable surface proteins, is required, along with reproducible disease models.

Mycoplasma genomes contain compact gene sets that approach the minimal complement necessary for life and reflect multiple evolutionary instances of genomic reduction. Lateral gene transfer may play a critical role in shaping the mobile gene pool in these organisms, yet complex mobile elements have not been reported within this genus. We describe here a large (ϳ23-kb) genetic element with unique features that is present in four copies in the Mycoplasma fermentans PG18 chromosome, accounting for approximately 8% of the genome. These novel elements, designated ICEF (integrative conjugal elements of M. fermentans), resemble conjugative, self-transmissible integrating elements (constins) in that circular, nonreplicative extrachromosomal forms occur in which the left and right termini of the integrated element are juxtaposed and separated by a coupling sequence derived from direct repeats flanking chromosomal copies of ICEF as a result of target site duplication. ICEF contain multiple similarly oriented open reading frames (ORFs), of which some have homology to products of known conjugation genes but others have no known counterparts. Surprisingly, unlike other constins, ICEF lack homologs of known integrases, transposases, or recombinases, suggesting that a novel enzyme may be employed for integration-excision. Skewed distribution and varied sites of chromosomal integration among M. fermentans isolates suggest a role for ICEF in promoting genomic and phenotypic variation in this species. Identification of homologs of terminal ICEF ORFs in two additional mycoplasma species indicates that ICEF is the prototype member of a family of ICE-related elements that may be widespread among pathogenic mycoplasmas infecting diverse vertebrate hosts.It is becoming increasingly appreciated that lateral gene transfer (LGT) has played a major role in bacterial evolution, disseminating key traits both within and among bacterial species. In contrast to evolution by random point mutation and subsequent selection for variants with improved fitness, acquisition of a new phenotype by LGT is considered a "quantum leap" in evolution (23), as the genes responsible for the phenotype are typically transferred laterally en bloc. Such a transfer also enables the trait to be more widely disseminated rather than relying on different bacterial clones to independently create de novo the desired mutation(s) that will confer increased fitness (41, 42).The extent to which LGT has shaped bacterial genomes has been revealed by assessment of proliferating genome sequence data. Not only the diverse forms of mobilizable gene pools but also the mechanisms of transfer and the types of element involved are becoming better defined (reviewed in references 15 and 47). Among naturally competent bacteria, transformation of naked DNA is likely to mediate genetic exchange within and between bacterial genera. In the context of large pathogenicity islands, the presence of bacteriophage-related sequences and their insertion into known prophage attachment sites implicate ...