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Background: Avian mycoplasmas are small bacteria associated with several pathogenic conditions in many wild and poultry bird species. Extensive genomic data are available for many avian mycoplasmas, yet no comparative studies focusing on this group of mycoplasmas have been undertaken so far. Results: Here, based on the comparison of forty avian mycoplasma genomes belonging to ten different species, we provide insightful information on the phylogeny, pan/core genome, energetic metabolism, and virulence of these avian pathogens. Analyses disclosed considerable inter- and intra-species genomic variabilities, with genome sizes that can vary by twice as much. Phylogenetic analysis based on concatenated orthologous genes revealed that avian mycoplasmas fell into either Hominis or Pneumoniae groups within the Mollicutes and could split into various clusters. No host co-evolution of avian mycoplasmas can be inferred from the proposed phylogenetic scheme. With 3,237 different gene clusters, the avian mycoplasma group under study proved diverse enough to have an open pan genome. However, a set of 150 gene clusters was found to be shared between all avian mycoplasmas, which is likely encoding essential functions. Comparison of energy metabolism pathways showed that avian mycoplasmas rely on various sources of energy. Superposition between phylogenetic and energy metabolism groups revealed that the glycolytic mycoplasmas belong to two distinct phylogenetic groups (Hominis and Pneumoniae), while all the arginine-utilizing mycoplasmas belong only to Hominis group. This can stand for different evolutionary strategies followed by avian mycoplasmas and further emphasizes the diversity within this group. Virulence determinants survey showed that the involved gene arsenals vary significantly within and between species, and could even be found in species often reported apathogenic. Immunoglobulin-blocking proteins were detected in almost all avian mycoplasmas. Although these systems are not exclusive to this group, they seem to present some particular features making them unique among mycoplasmas. Conclusion: This comparative genomic study uncovered the significant variable nature of avian mycoplasmas, furthering our knowledge on their biological attributes and evoking new hallmarks. [ABSTRACT FROM AUTHOR]

bla NDM , the most prevalent carbapenemase among carbapenem-resistant Enterobacteriaceae, is thought to have emerged in India, as its initial detection in 2008 was linked to this country, and subsequent retrospective surveys had so far established the earliest bla NDM -positive strains to be isolated in India in 2005. Molecular dating and analyses suggest bla NDM emerged within Acinetobacter species decades prior to 2005 on a Tn 125 transposon. Despite early reports of elevated rates of carbapenem-resistant Acinetobacter species in Israel starting in the 1990s, limited molecular data are available from this location. We searched for bla NDM among Acinetobacter species isolated in Israel between 2001 and 2006. One A. junii strain, Ajun-H1-3, isolated in January 2004, carried bla NDM-1 within a Tn 125 -like transposon on a 49-kb plasmid, pNDM-Ajun-H1-3, making Ajun-H1-3 the earliest NDM-positive isolate observed to date. The pNDM-Ajun-H1-3 plasmid matched numerous BJ01-like NDM-positive plasmids identified from 2005 onward in Acinetobacter species as well as Enterobacterales. These results indicate the need for further retrospective work on global strain archives to shed light on the conditions favoring the emergence as well as subsequent evolution and spread of bla NDM ., Importance: This study presents the earliest observation of bla NDM-1 , isolated in a geographical region distant from where it is believed to have originated. In doing so, this study provides novel insights into the emergence and spread of bla NDM , the most prevalent carbapenemase among carbapenem-resistant Enterobacteriaceae, and its associated mobile genetic elements. It also sheds light on the conditions that foster the evolution of antimicrobial resistance, one of the greatest public health challenges we face., Competing Interests: The authors declare no conflict of interest.

Clustered regularly interspaced short palindromic repeat (CRISPR)-Cas systems are bacterial defences that target bacteriophages and mobile genetic elements. How these defences evolve in novel host environments remains largely unknown. We studied the evolution of the CRISPR-Cas system in Mycoplasma gallisepticum (also named Mycoplasmoides gallisepticum ), a bacterial pathogen of poultry that jumped into a passerine host ~30 years ago. Over the decade following the host shift, all isolates displaying a functional CRISPR-Cas system were found not only to harbour completely new sets of spacers, but the DNA protospacer adjacent motif recognized by the main effector M. gallisepticum Cas9 (MgCas9) was also different. These changes in CRISPR-Cas diversity and specificity are consistent with a change in the community of phages and mobile elements infecting M. gallisepticum as it colonized the novel host. In the years following the host shift, we also detected a gradual rise in isolates displaying non-functional MgCas9. After 12 years, all circulating isolates harboured inactive forms only. This loss of CRISPR-Cas function comes at a time when the passerine host is known to have evolved widespread resistance, which in turn drove the evolution of increasing M. gallisepticum virulence through antagonistic coevolution. Such striking concordance in the rise of inactivated forms of CRISPR-Cas and the evolution of host resistance suggests that the inactivation of the CRISPR-Cas system was necessary for enabling adaptive bacterial responses to host-driven selection. We highlight the need to consider both host and pathogen selection pressures on bacteria for understanding the evolution of CRISPR-Cas systems and the key factors driving the emergence of a pathogenic bacterium in a novel host.

Genome-based analysis allows for large-scale classification of diverse bacteria and has been widely adopted for delineating species. Unfortunately, for higher taxonomic ranks such as genus, establishing a generally accepted approach based on genome analysis is challenging. While core-genome phylogenies depict the evolutionary relationships among species, determining the correspondence between clades and genera may not be straightforward. For genotypic divergence, the percentage of conserved proteins and genome-wide average amino acid identity are commonly used, but often do not provide a clear threshold for classification. In this work, we investigated the utility of global comparisons and data visualization in identifying clusters of species based on their overall gene content and rationalized that such patterns can be integrated with phylogeny and other information such as phenotypes for improving taxonomy. As a proof of concept, we selected 177 representative genome sequences from the Mycoplasmatales-Entomoplasmatales clade within the class Mollicutes for a case study. We found that the clustering patterns corresponded to the current understanding of these organisms, namely the split into three above-genus groups: Hominis, Pneumoniae and Spiroplasma-Entomoplasmataceae -Mycoides. However, at the genus level, several important issues were found. For example, recent taxonomic revisions that split the Hominis group into three genera and Entomoplasmataceae into five genera are problematic, as those newly described or emended genera lack clear differentiations in gene content from one another. Moreover, several cases of misclassification were identified. These findings demonstrated the utility of this approach and its potential application to other bacteria.

A necropsy was performed on a Common Raven ( Corvus corax ) presenting an opportunistic fungal respiratory infection and a bursal lymphoid depletion with inclusion bodies, suggestive of a circovirus infection. High-throughput sequencing of circular DNA in the bursa of Fabricius revealed a complete genome sequence of a Circovirus pigeon strain., Competing Interests: The authors declare no conflict of interest.

The development of synthetic genomics (SG) allowed the emergence of several groundbreaking techniques including the synthesis, assembly and engineering of whole bacterial genomes. The successful implantation of those methods, which culminated in the creation of JCVI-syn3.0 the first nearly minimal bacterium with a synthetic genome, mainly results from the use of the yeast Saccharomyces cerevisiae as a transient host for bacterial genome replication and modification. Another method played a key role in the resounding success of this project: bacterial genome transplantation (GT). GT consists in the transfer of bacterial genomes cloned in yeast, back into a cellular environment suitable for the expression of their genetic content. While successful using many mycoplasma species, a complete understanding of the factors governing GT will most certainly help unleash the power of the entire SG pipeline to other genetically intractable bacteria., (© 2019 médecine/sciences – Inserm.)

The past decade has seen vast improvements in DNA synthesis and assembly methods. The creation of synthetic DNA molecules is becoming easier and more affordable, such that entire chromosomes can now be synthesized. These advances mark the beginning of synthetic genomics, a new discipline interested in the construction of complete genomes tailored for the study and application of biological systems. From viral genome synthesis to the reconstruction of the yeast 16 chromosomes, we discuss the main discoveries, the regulations and ethical considerations along with the potential of this emerging discipline for the future., (© 2019 médecine/sciences – Inserm.)

Cloning and transplantation of bacterial genomes is a powerful method for the creation of engineered microorganisms. However, much remains to be understood about the molecular mechanisms and limitations of this approach. We report the whole-genome cloning of Mesoplasma florum in Saccharomyces cerevisiae, and use this model to investigate the impact of a bacterial chromosome in yeast cells. Our results indicate that the cloned M. florum genome is subjected to weak transcriptional activity, and causes no significant impact on yeast growth. We also report that the M. florum genome can be transplanted into Mycoplasma capricolum without any negative impact from the putative restriction enzyme encoding gene mfl307. Using whole-genome sequencing, we observed that a small number of mutations appeared in all M. florum transplants. Mutations also arose, albeit at a lower frequency, when the M. capricolum genome was transplanted into M. capricolum recipient cells. These observations suggest that genome transplantation is mutagenic, and that this phenomenon is magnified by the use of genome donor and recipient cell belonging to different species. No difference in efficiency was detected after three successive rounds of genome transplantation, suggesting that the observed mutations were not selected during the procedure. Taken together, our results provide a more accurate picture of the events taking place during bacterial genome cloning and transplantation.