Hello readers!

It’s the new year and #microtwjc is back. Please join Danny (@id_EATER) and Phil (@wragbags) at 20:00 (GMT) on twitter to discuss this paper from the folks at the Pasteur Institute. This group works on the bacterium Helicobacter Pylori which is associated with gastritis and peptic ulcers. As you might guess this means it has special adaptations to thrive in the acidic conditions of the stomach!

The paper we will discuss is titled: Evolution of Helicobacter: Acquisition by Gastric Species of Two Histidine-Rich Proteins Essential for Colonization. It takes an initial observation in the literature though a comparative genomics approach to in vitro experiments and finally into a in vivo system in order to explain a role of two proteins in gastric colonization by Helicobacter.

Please keep the following discussion points/questions in mind when reading the paper and feel free to tweet to @microtwjc or comment below with any points/questions you might have during reading.

  1. What was known about the subject before this paper was published? How do the authors make it easy to contextualize their findings in the field?
  2. What have we learnt after reading the paper?
  3. How does the data support the conclusions and what are some limitations in the experimental design?
  4. What was done well in this paper?
  5. What future work would be of interest to conduct?

You can read the full paper here and I have included the abstract and author summary after the jump. Hope to see you online!

Read the rest of this entry »

This week for MicroTwJC, we look at how gut microbiota change and adapt while the gut itself is being destroyed and remade when caterpillars turn into butterflies.

When  a caterpillar becomes chrysalis, it marks the beginning of an incredible transformation, which is shown in the video above. It’s internal organs change and reform, muscles break apart and reform into new shapes, and organs shift and change.

But that isn’t all that change. These caterpillars are host to a range of microbiota in its gut. The delicate balance between the host and its symbionts must be maintained. This paper investigates how this balance is maintained.

Join us next Tuesday at 8pm. Tweet into #microTwJC, and follow the discussion on Twitter, or via Tweetchat.

Link to the paper: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0086995 

Host and Symbiont Jointly Control Gut Microbiota during Complete Metamorphosis

The majority of animals are holometabolous insects and change dramatically through development. They undergo a dramatic transformation from a larval stage, adapted to feed, to an adult separated by a pupal stage. During this pupal stage the majority of the organs are renewed including the gut. This creates a risky situation that we study here: when the gut is renewed insects risk losing beneficial microbiota while simultaneously being at risk of opportunistic infection. Here, by manipulating host and symbiont we show how host and symbiont succeed in jointly controlling opportunistic pathogens. If one or both of the partners are compromised, opportunistic pathogens dominate the gut microbiota resulting in increased mortality. These findings may be broadly applicable to insects with complete metamorphosis, including many disease vectors.

Tuesday’s #microtwjc (8pm GMT) will be looking at this paper:

The soft palate is an important site of adaptation for transmissible influenza viruses


Influenza A viruses pose a major public health threat by causing seasonal epidemics and sporadic pandemics. Their epidemiological success relies on airborne transmission from person to person; however, the viral properties governing airborne transmission of influenza A viruses are complex. Influenza A virus infection is mediated via binding of the viral haemagglutinin (HA) to terminally attached α2,3 or α2,6 sialic acids on cell surface glycoproteins. Human influenza A viruses preferentially bind α2,6-linked sialic acids whereas avian influenza A viruses bind α2,3-linked sialic acids on complex glycans on airway epithelial cells1, 2. Historically, influenza A viruses with preferential association withα2,3-linked sialic acids have not been transmitted efficiently by the airborne route in ferrets3, 4. Here we observe efficient airborne transmission of a 2009 pandemic H1N1 (H1N1pdm) virus (A/California/07/2009) engineered to preferentially bind α2,3-linked sialic acids. Airborne transmission was associated with rapid selection of virus with a change at a single HA site that conferred binding to long-chain α2,6-linked sialic acids, without loss of α2,3-linked sialic acid binding. The transmissible virus emerged in experimentally infected ferrets within 24 hours after infection and was remarkably enriched in the soft palate, where long-chain α2,6-linked sialic acids predominate on the nasopharyngeal surface. Notably, presence of long-chain α2,6-linked sialic acids is conserved in ferret, pig and human soft palate. Using a loss-of-function approach with this one virus, we demonstrate that the ferret soft palate, a tissue not normally sampled in animal models of influenza, rapidly selects for transmissible influenza A viruses with human receptor (α2,6-linked sialic acids) preference.



See you on Tuesday!!!


Tuesday’s #microtwjc (8pm GMT) will be looking at this paper:

Active Transport of Phosphorylated Carbohydrates Promotes Intestinal Colonization and Transmission of a Bacterial Pathogen

Brandon Sit , Shauna M. Crowley , Kirandeep Bhullar, Christine Chieh-Lin Lai, Calvin Tang, Yogesh Hooda, Charles Calmettes, Husain Khambati, Caixia Ma, John H. Brumell, Anthony B. Schryvers, Bruce A. Vallance , Trevor F. Moraes



Efficient acquisition of extracellular nutrients is essential for bacterial pathogenesis, however the identities and mechanisms for transport of many of these substrates remain unclear. Here, we investigate the predicted iron-binding transporter AfuABC and its role in bacterial pathogenesis in vivo. By crystallographic, biophysical and in vivo approaches, we show that AfuABC is in fact a cyclic hexose/heptose-phosphate transporter with high selectivity and specificity for a set of ubiquitous metabolites (glucose-6-phosphate, fructose-6-phosphate and sedoheptulose-7-phosphate). AfuABC is conserved across a wide range of bacterial genera, including the enteric pathogens EHEC O157:H7 and its murine-specific relative Citrobacter rodentium, where it lies adjacent to genes implicated in sugar sensing and acquisition. C. rodentium ΔafuA was significantly impaired in an in vivo murine competitive assay as well as its ability to transmit infection from an afflicted to a naïve murine host. Sugar-phosphates were present in normal and infected intestinal mucus and stool samples, indicating that these metabolites are available within the intestinal lumen for enteric bacteria to import during infection. Our study shows that AfuABC-dependent uptake of sugar-phosphates plays a critical role during enteric bacterial infection and uncovers previously unrecognized roles for these metabolites as important contributors to successful pathogenesis.

Author Summary

Essentially all Gram-negative pathogens are reliant on specific transport machineries termed binding protein-dependent transporters (BPDTs) to transport solutes such as amino acids, sugars and metal ions across their membranes. In this study we investigated AfuABC, a predicted iron-transporting BPDT found in many bacterial pathogens. We show by structural and functional approaches that AfuABC is not an iron transporter. Instead, AfuABC is a trio of proteins that bind and transport sugar-phosphates such as glucose-6-phosphate (G6P). In doing so, we present the first structural solution of a G6P-specific transport protein and add to the few known unique machineries for sugar-phosphate uptake by bacteria. Furthermore, we show that AfuABC is required by the intestinal pathogen C. rodentium to effectively transmit between mice and re-establish infection, leading us to propose that the transport of sugar-phosphates is an important part of general bacterial pathogenesis.


Discussion points to follow…

First and foremost, apologies for the late posting of this article! What with the rugby world cup and everything in work it has just been an immense couple of weeks.  But alas, the paper is here!

The paper has been chosen by myself (@sbi5ar) and will be discussed with the help of Nel (@helloitsnel).


A novel siderophore system is essential for the growth of Pseudomonas aeruginosa in airway mucus


Pseudomonas aeruginosa establishes airway infections in Cystic Fibrosis patients. Here, we investigate the molecular interactions between P. aeruginosa and airway mucus secretions (AMS) derived from the primary cultures of normal human tracheal epithelial (NHTE) cells. PAO1, a prototype strain of P. aeruginosa, was capable of proliferating during incubation with AMS, while
all other tested bacterial species perished. A PAO1 mutant lacking PA4834 gene became susceptible to AMS treatment. The ΔPA4834 mutant was grown in AMS supplemented with 100 μM ferric iron, suggesting that the PA4834 gene product is involved in iron metabolism. Consistently, intracellular iron content was decreased in the mutant, but not in PAO1 after the AMS treatment. Importantly,
a PAO1 mutant unable to produce both pyoverdine and pyochelin remained viable, suggesting that these two major siderophore molecules are dispensable for maintaining viability during incubation with AMS. The ΔPA4834 mutant was regrown in AMS amended with 100 μM nicotianamine, a phytosiderophore whose production is predicted to be mediated by the PA4836 gene. Infectivity of the ΔPA4834 mutant was also significantly compromised in vivo. Together, our results identify a genetic element encoding a novel iron acquisition system that plays a previously undiscovered role in P. aeruginosa airway infection.


1. Is this paper well written and easy to understand?

2. Does the introduction set the scene for the research presented?

3. Do the methods appear reliable and are they well explained?

4. Do the results and discussion make sense?

5. What (if any) future work could lead on from this?

In addition to these questions, hopefully we can explore whether the clinical significance that the paper portrays is justified though the research methods that have been used.

See you all next Tuesday (20th October 2015) at 20:00 (08:00 pm) BST


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