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I’m afraid this session’s transcript is embedded (I got swamped by work, then storify and I had an argument – it lost all of the tweets I added – and then I fell out with Twitter). This means it is HUGE. It may take a long time to open…

Apologies if I missed anyone out – just let me know in the comments and I will edit you in.
Apologies also that this may be out of order slightly – the date stamp only had the minutes and not the seconds so there may be the odd tweet mix-up.

To see the transcript click below…

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The paper this week is from PLoS Genetics, concerning the mechanisms of adaptation of Bartonella spp. to their mammalian hosts.

The PLoS journals give a good accessible overview of there papers so here is the author summary:

Adaptive radiation is the rapid origination of an array of species by the divergent colonization of disparate ecological niches. In the case of pathogenic bacteria, radiations can lead to the emergence of novel human pathogens. Being divergently adapted to a range of different mammalian hosts, including humans as reservoir or incidental hosts, the genus Bartonella represents a suitable model to study genomic mechanisms underpinning divergent adaptation of pathogens. Here we show that two distinct lineages of Bartonella have radiated in parallel, resulting in two arrays of evolutionary distinct species adapted to overlapping sets of mammalian hosts. Such parallelisms display excellent models to reveal insights into the genetic mechanisms underlying these independent evolutionary processes. Our genome-wide analysis identifies a striking evolutionary parallelism in a horizontally-acquired protein secretion system in the two lineages. The parallel evolutionary trajectory of this system in the two lineages is characterized by the convergent origination of a wide array of adaptive functions dedicated to the cellular interaction within the mammalian hosts. The parallel evolution of the two radiating lineages on the ecological as well as on the molecular level suggests that the horizontal acquisition and the functional diversification of the secretion system display an evolutionary key innovation underlying adaptive evolution.

Discussion points

  1. Were the aims of the study clear?
  2. Were the findings clearly supported by the data?
  3. What relevance does understanding the mechanisms driving diversification have for human health?
  4. Could any additional experiments improve the study?
 Join us for discussion Tuesday 25th September at 8pm UK time for #microtwjc

Next week’s #microtwjc paper comes from the September 2012 issue of the SGM’s ‘Microbiology’ and is titled:

Molecular characterization of a novel mosaic tet(S/M) gene encoding tetracycline resistance in foodborne strains of Streptococcus bovis

Simona Barile, Chiara Devirgiliis, and Giuditta Perozzi

(Microbiology September 2012 158:2353-2362; published ahead of print June 21, 2012, doi:10.1099/mic.0.058206-0 )

The abstract:

The presence of antibiotic-resistance (AR) genes in foodborne bacteria of enteric origin represents a relevant threat to human health in the case of opportunistic pathogens, which can reach the human gut through the food chain. Streptococcus bovis is a human opportunistic pathogen often associated with infections in immune-compromised or cancer patients, and it can also be detected in the environment, including fermented foods. We have focused on the molecular characterization of a tetracycline (Tet)-resistance gene present in 39 foodborne isolates of S. bovis phenotypically resistant to this drug. The gene was identified as a novel tet(S/M) fusion, encoding a mosaic protein composed of the N-terminal 33 amino acids of Tet(S), in-frame with the Tet(M) coding sequence. Heterologous expression of the mosaic gene was found to confer Tet resistance upon Escherichia coli recipients. Moreover, the tet(S/M) gene was found to be transcriptionally inducible by Tet under the endogenous tet(S) promoter in both S. bovis and E. coli. Nucleotide sequencing of the surrounding genomic region of 16.2 kb revealed large blocks of homology with the genomes of Streptococcus infantarius and Lactococcus lactis. A subregion of about 4 kb containing mosaic tet(S/M) was flanked by two copies of the IS1216 mobile element. PCR amplification with primers directed outwards from the tet(S/M) gene identified the presence of a 4.3 kb circular form corresponding to the intervening chromosomal region between the two IS1216 elements, but lacking a replication origin. The circular element shared extensive overall homology with a region of the multidrug-resistance plasmid pK214 from Lc. lactis, containing tet(S), as well as the IS1216 transposase-containing element and intervening non-coding sequences. Linear reconstruction of the insertion events likely to have occurred within this genomic region, inferred from sequence homology, provides further evidence of the chromosomal rearrangements that drive genomic evolution in complex bacterial communities such as the gut and food microbiota.


A few discussion points to consider (if you have any other points please comment below)

  1. Was the paper well written, clearly laid out and easy to follow?
  2. Were the experiments well designed?  Were there any experiments you would have liked to see there that weren’t?
  3. How does this work contribute to our knowledge of antibiotic resistance and are there any practical suggestions/outcomes/considerations that stem from this work?
  4. If you were the researchers what future work would you want to do?


We hope you can join us next week, Tues 11th September, 8pm UK time for #microtwjc 🙂


With thanks to CRV Arnhem for making this available via a Creative Commons licence