MicrobiologyBytes

Ah, nanotechnology – the great salvation of humankind that will cure cancer, solve the energy crisis and provide for our eco-friendly manufacturing future. That’s assuming that we can figure out how to build the nanomachines we need of course. Which is where this comes in:

“The swimming of the marine cyanobacterium Synechococcus has been a longstanding puzzle. Synechococcus is ubiquitous in the euphotic zone of the worlds oceans making it a major primary producer. Approximately one third of the open ocean isolates are motile. It moves through seawater at speeds of 5 to 25 m/s while rotating about its long axis at about 1 Hz. It accomplishes this despite the complete absence of any observable motile apparatus such as flagella. A clue to Synechococcus’s propulsion comes from a bacterium that does not swim, but glides on surfaces…”

On the Mysterious Propulsion of Synechococcus. (2012) PLoS ONE 7(5): e36081. doi:10.1371/journal.pone.0036081
We propose a model for the self-propulsion of the marine bacterium Synechococcus utilizing a continuous looped helical track analogous to that found in Myxobacteria. In our model cargo-carrying protein motors, driven by proton-motive force, move along a continuous looped helical track. The movement of the cargo creates surface distortions in the form of small amplitude traveling ridges along the S-layer above the helical track. The resulting fluid motion adjacent to the helical ribbon provides the propulsive thrust. A variation on the helical rotor model allows the motors to be anchored to the peptidoglycan layer, where they drive rotation of the track creating traveling helical waves along the S-layer. We derive expressions relating the swimming speed to the amplitude, wavelength, and velocity of the surface waves induced by the helical rotor, and show that they fall in reasonable ranges to explain the velocity and rotation rate of swimming Synechococcus.

I promised I would write about the first Microbiology Twitter Journal Club (#microtwjc), held yesterday, so here it is. Click through the images below for larger versions. As ever, I am grateful for the invaluable help of Martin Hawksey.

The Network:

78 people used that hashtag (not all during the live session, these numbers include the runup period), with at least 131 conversations (in the jargon, 78 nodes, 131 edges). For a live view of the network (very exciting, recommended :-), click this link.

The Content:

Summarized here in a word cloud from Wordle.net. This is the complete archive from the hashtag.

The People:

Tweet Sources (devices):

So where do we go from here? Onwards, clearly :-) I’m really looking forward to the next journal club. Stay tuned to #microtwjc for details. It is important that this remains a student-led process, but it would be great to have some more academics contributing (without taking over).

A key aspect for success is choosing the right paper, which needs to be interesting, high quality, but with enough uncertainly to promote discussion. The danger is burnout for the organizers, who are also busy doing lots of other things. It’s up to the community to help out by suggesting suitable papers for discussion via the hashtag so that all the burden of organizing doesn’t fall on a few people.

Should authors be invited to take part? I see no harm in this as long as they are given adequate notice, although I suspect that most will not want to. The other option is to try to invite one or two subject “experts” for each paper.

I’m sure other people will have further suggestions, so let’s hear them. We’re off to a great start!

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Bacterial cell shape is dictated by the composition of the cell envelope component peptidoglycan. Some important pathogens have a characteristic helical corkscrew morphology that may help them burrow into mucus overlaying cells to initiate colonization and pathogenicity. One example is Campylobacter jejuni, the leading cause of bacterial-induced diarrheal disease in the developed world.

Direct evidence supporting the hypothesis that C. jejuni shape is related to its pathogenicity traits has not previously been provided. Researchers have identified a gene encoding a peptidase modifying peptidoglycan that is essential for maintaining the C. jejuni corkscrew shape. We can now connect a C. jejuni gene with morphology and peptidoglycan biosynthesis. Loss of this gene was also found to affect pathogenic attributes such as chicken colonization, biofilms, motility, and activation of host inflammatory mediators. In addition, this is the first study to thoroughly characterize C. jejuni peptidoglycan structure and to identify a gene involved in peptidoglycan maintenance.

These findings highlight an emerging theme in bacterial pathogenesis research: the connection between bacterial cell biology and pathogenesis. Finally, characterization of C. jejuni cell shape and peptidoglycan provides a starting point for further work in this area in C. jejuni and other bacteria with curved and helical morphologies.

Peptidoglycan-Modifying Enzyme Pgp1 Is Required for Helical Cell Shape and Pathogenicity Traits in Campylobacter jejuni. (2012) PLoS Pathog 8(3): e1002602. doi:10.1371/journal.ppat.1002602
The impact of bacterial morphology on virulence and transmission attributes of pathogens is poorly understood. The prevalent enteric pathogen Campylobacter jejuni displays a helical shape postulated as important for colonization and host interactions. However, this had not previously been demonstrated experimentally. C. jejuni is thus a good organism for exploring the role of factors modulating helical morphology on pathogenesis. We identified an uncharacterized gene, designated pgp1 (peptidoglycan peptidase 1), in a calcofluor white-based screen to explore cell envelope properties important for C. jejuni virulence and stress survival. Bioinformatics showed that Pgp1 is conserved primarily in curved and helical bacteria. Deletion of pgp1 resulted in a striking, rod-shaped morphology, making pgp1 the first C. jejuni gene shown to be involved in maintenance of C. jejuni cell shape. Pgp1 contributes to key pathogenic and cell envelope phenotypes. In comparison to wild type, the rod-shaped pgp1 mutant was deficient in chick colonization by over three orders of magnitude and elicited enhanced secretion of the chemokine IL-8 in epithelial cell infections. Both the pgp1 mutant and a pgp1 overexpressing strain – which similarly produced straight or kinked cells – exhibited biofilm and motility defects. Detailed peptidoglycan analyses via HPLC and mass spectrometry, as well as Pgp1 enzyme assays, confirmed Pgp1 as a novel peptidoglycan DL-carboxypeptidase cleaving monomeric tripeptides to dipeptides. Peptidoglycan from the pgp1 mutant activated the host cell receptor Nod1 to a greater extent than did that of wild type. This work provides the first link between a C. jejuni gene and morphology, peptidoglycan biosynthesis, and key host- and transmission-related characteristics.

Don’t understand how cell shape can affect pathogenesis? Neither do I! That’s why I’ll be at #microtwjc at 8pm UK time tonight!

Yuan Chang & Patrick Moore present the Marjory Stephenson Prize Lecture ‘Old themes and new variations in human tumour virology’ on 27 March at the Society for General Microbiology’s Spring Conference 2012 in Dublin.

A new online microbiology journal club will take place on alternate Tuesdays at 8pm UK Time (GMT+1) and aims to cover topics across the whole spectrum of microbiology. The first paper (for 8th May) is:

Peptidoglycan-Modifying Enzyme Pgp1 Is Required for Helical Cell Shape and Pathogenicity Traits in Campylobacter jejuni. (2012) PLoS Pathog 8(3): e1002602.
“Bacterial cell shape is dictated by the composition of the cell envelope component peptidoglycan. Some important pathogens have a characteristic helical corkscrew morphology that may help them burrow into mucus overlaying cells to initiate colonization and pathogenicity. One example is Campylobacter jejuni, the leading cause of bacterial-induced diarrheal disease in the developed world. Direct evidence supporting the hypothesis that C. jejuni shape is related to its pathogenicity traits has not previously been provided. We identified a gene encoding a peptidase modifying peptidoglycan that is essential for maintaining the C. jejuni corkscrew shape. We can now connect a C. jejuni gene with morphology and peptidoglycan biosynthesis. Loss of this gene was also found to affect pathogenic attributes such as chicken colonization, biofilms, motility, and activation of host inflammatory mediators. In addition, this is the first study to thoroughly characterize C. jejuni peptidoglycan structure and to identify a gene involved in peptidoglycan maintenance. Our findings highlight an emerging theme in bacterial pathogenesis research: the connection between bacterial cell biology and pathogenesis. Finally, our characterization of C. jejuni cell shape and peptidoglycan provides a starting point for further work in this area in C. jejuni and other bacteria with curved and helical morphologies.”

How do you take part in an online journal club?

• Read the paper (above)
• Be on Twitter at 8pm UK time on Tuesday 8th May
• Follow the #microtwjc hashtag
• Join in!

• More about Campylobacter jejuni (this will help you look smart on Tuesday ;-)

“So let us invite ourselves to commit to Open Discourse. Let us set the tone and establish the precedent of enlightened debate that is public spirited, as well as public. Let us refrain from contributing the inconsequential, the self serving and the counterproductive. And above all, let us remember that discourse need not be discourteous. I encourage all of us to not only participate in this movement, but to promote it. Tell a friend. Tell a mentor. Tell a protégé. Start submitting comments. In the end the value we receive will be the value we give. And the value to the world will be greater still.”
Beyond open access: open discourse, the next great equalizer. (2006) Retrovirology 2006, 3: 55 doi:10.1186/1742-4690-3-55

The oncogenic potential of papillomaviruses (PVs) has been appreciated since the 1930s yet the mechanisms of virus-mediated cellular transformation are still being revealed. Reasons for this include:

• the oncoproteins are multifunctional
• there is an ever-growing list of cellular interacting proteins
• more than one cellular protein may bind to a given region of the oncoprotein
• there is only limited information on the proteins encoded by the corresponding non-oncogenic papillomaviruses

The perspective of this review is to contrast the activities of the viral E6 and E7 proteins encoded by the oncogenic human PVs (termed high-risk HPVs) to those encoded by their non-oncogenic counterparts (termed low-risk HPVs) in an attempt to sort out viral life cycle-related functions from oncogenic functions. The review emphasizes lessons learned from the cell culture studies of the HPVs causing mucosal/genital tract cancers.

Cellular transformation by human papillomaviruses: Lessons learned by comparing high- and low-risk viruses. (2012) Virology 424(2): 77-98

At the turn of the 19th century, trypanosomes were identified as the causative agent of sleeping sickness and their presence within the cerebrospinal fluid of late stage sleeping sickness patients was described. However, no definitive proof of how the parasites reach the brain has been presented so far.

Analyzing electron micrographs prepared from rodent brains more than 20 days after infection, this paper presents conclusive evidence that the parasites first enter the brain via the choroid plexus from where they penetrate the epithelial cell layer to reach the ventricular system. Adversely, no trypanosomes were observed within the parenchyma outside blood vessels. It shows that brain infection depends on the formation of long slender trypanosomes and that the cerebrospinal fluid as well as the stroma of the choroid plexus is a hostile environment for the survival of trypanosomes. The data suggest that trypanosomes do not intend to colonize the brain but reside near or within the glia limitans, from where they can re-populate blood vessels and disrupt the sleep wake cycles.

Late Stage Infection in Sleeping Sickness. (2012) PLoS ONE 7(3): e34304. doi:10.1371/journal.pone.0034304

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Human papillomavirus type 16 is the main etiological agent of cervical cancer. Despite advances in our understanding of transformation and cancer progression, as well as preventative vaccination strategies, the early events in papillomavirus infections are incompletely understood.

This paper investigates which strategies and cellular mechanisms the virus uses to enter epithelial cells. Entry was slow and asynchronous likely due to several structural alterations, which needed to occur on the cell exterior. Interestingly, the virus hijacked a potentially novel pathway of endocytosis for entry, which was distinct from classical macropinocytosis. This cellular mechanism may also be used by other viruses such as influenza A virus, echo virus 1, and choriomeningitis virus.

Entry of Human Papillomavirus Type 16 by Actin-Dependent, Clathrin- and Lipid Raft-Independent Endocytosis. (2012) PLoS Pathog 8(4): e1002657. doi:10.1371/journal.ppat.1002657
Infectious endocytosis of incoming human papillomavirus type 16 (HPV-16), the main etiological agent of cervical cancer, is poorly characterized in terms of cellular requirements and pathways. Conflicting reports attribute HPV-16 entry to clathrin-dependent and -independent mechanisms. To comprehensively describe the cell biological features of HPV-16 entry into human epithelial cells, we compared HPV-16 pseudovirion (PsV) infection in the context of cell perturbations (drug inhibition, siRNA silencing, overexpression of dominant mutants) to five other viruses (influenza A virus, Semliki Forest virus, simian virus 40, vesicular stomatitis virus, and vaccinia virus) with defined endocytic requirements. Our analysis included infection data, i.e. GFP expression after plasmid delivery by HPV-16 PsV, and endocytosis assays in combination with electron, immunofluorescence, and video microscopy. The results indicated that HPV-16 entry into HeLa and HaCaT cells was clathrin-, caveolin-, cholesterol- and dynamin-independent. The virus made use of a potentially novel ligand-induced endocytic pathway related to macropinocytosis. This pathway was distinct from classical macropinocytosis in regards to vesicle size, cholesterol-sensitivity, and GTPase requirements, but similar in respect to the need for tyrosine kinase signaling, actin dynamics, Na+/H+ exchangers, PAK-1 and PKC. After internalization the virus was transported to late endosomes and/or endolysosomes, and activated through exposure to low pH.

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Microbial diseases occur as a result of multifarious host-pathogen interactions. However, invading pathogens encounter a large number of different harmless and beneficial bacterial species, which colonize and reside in the host. Surprisingly, there has been little study of the possible interactions between incoming pathogens and the resident bacterial community. Recent studies have revealed that resident bacteria assist different types of incoming pathogens via a wide variety of mechanisms including cell-cell signaling, metabolic interactions, evasion of the immune response and a resident-to-pathogen switch. This calls for serious consideration of pathogen-microbe interactions in the host with respect to disease severity and progression.

Incoming pathogens team up with harmless ‘resident’ bacteria. 2012 Trends Microbiol. 20(4): 160-164

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