Tag Archives: infection

Friday Fellow: H. pylori

by Piter Kehoma Boll

I already introduced three species of bacteria here, all of them free-living and/or friendly little ones. But we all know that many bacteria can be a real annoyance to us humans, and so it’s time to show some of those, right?

I decided to start with one that I thought to have living inside me some time ago (but it happened that I don’t), and this is the ill-tempered Helicobacter pylori, which as usual lacks a common name, but is commonly called H. pylori for short by doctors, so that’s how I’ll call it.

empylori

Electron micrograph of a specimen of H. pylori showing the flagella.

The most common place to find the H. pylori is in the stomach. It is estimated that more than half of the human population has this bacterium living in their gastrointestinal tract, but in most cases it does not affect your life at all. However, sometimes it can mess things up.

H. pylori is a 3-µm long bacterium with the shape of a twisted rod, hence the name Helicobacter, meaning “helix rod”. It also has a set of four to six flagella at one of its ends, which make it a very motile bacterium. The twisted shape, together with the flagella, is thought to be useful for H. pylori to penetrate the mucus lining the stomach. It does so to escape from the strongly acidic environment of the stomach, always penetrating towards a less acidic place, eventually reaching the stomach epithelium and sometimes even living inside the epithelial cells.

In order to avoid even more the acids, H. pylori produces large amounts of urease, an enzyme that digest the urea in the stomach, producing ammonia, which is toxic to humans. The presence of H. pylori in the stomach may lead to inflammation as an imune response of the host, which increases the chances of the mucous membranes of the stomach and the duodenum to be harmed by the strong acids, leading to gastritis and eventually ulcers.

The association between humans and H. pylori seem to be very old, possibly as old as the human species itself, as its origin was traced back to East Africa, the cradle of Homo sapiens. This bacterium is, therefore, an old friend and foe and it will likely continue with us for many many years in the future.

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References:

Linz, B.; Balloux, F.; Moodley, Y. et al. (2007) An African origin for the intimate association between humans and Helicobacter pyloriNature 445: 915–918. https://dx.doi.org/10.1038/nature0556

Wikipedia. Helicobacter pylori. Available at < https://en.wikipedia.org/wiki/Helicobacter_pylori >. Access on August 5, 2017.

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Filed under Bacteria, Friday Fellow, Parasites

Friday Fellow: Operculate Acrochaete

by Piter Kehoma Boll

Last week I introduced a red alga, the Irish moss. Today I’m bringing another alga, this time a green one, but this is not an ordinary green alga, but a parasite of the Irish moss! So let’s talk about Acrochaete operculata, or the operculate acrochaete as I decided to call it in English, since obviously there would be no common name for an alga parasite of another alga.

Discovered and named in 1988, the operculate acrochaete is an exclusive parasite of Chondrus crispus. The infection occurs when flagellate zoospores of the parasite settle on the outer cell wall of the Irish Moss, where they start their development and digest the cell wall, penetrating the tissues of the host. In sporophytes of the Irish moss, the operculate acrochaete digests the intercellular matrix and spreads through the frond, while in gametophytes the infections remains localized, forming papules. The damages caused by the green alga lead to secondary infections by other organisms, especially bacteria, and the infected fronds end up falling apart, completely degradated.

ccrispus

A frond of the host (Chondrus crispus) to the left and the parasitic Acrochaete operculata that infects its tissues to the right. Photo extracted from chemgeo.uni-jena.de

As mentioned last week, the sporophytes and gametophytes of the Irish Moss have different forms of the polysaccharide carrageenan and this seems to be the reason why the parasite infects both forms differently. The sporophytes have lambda-carrageenan, which seems to increase the virulence of the parasite, while the kappa-carrageenan of the gametophyte seems to limit the green alga’s spread.

Since its discovery, the operculate acrochaete and its interaction with the Irish moss has been studied as a way to both reduce its damage on cultivated crops of the red alga and as a model to understand the relationship of plants and their pathogens.

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References:

Bouarab, K.; Potin, P.; Weinberger, F.; Correa, J.; Kloareg, B. (2001) The Chondrus crispus-Acrochaete operculata host-pathogen association, a novel model in glycobiology and applied phycopathology. Journal of Applied Phycology 13(2): 185-193.

Correa, J. A.; McLachlan, J. L. (1993) Endophytic algae of Chondrus crispus (Rhodophyta). V. Fine structure of the infection by Acrochaete operculata (Chlorophyta). European Journal of Phycology 29(1): 33–47. http://dx.doi.org/10.1080/09670269400650461

Correa, J. A.; Nielsen, R.; Grund, D. W. (1988) Endophytic algae of Chondrus crispus (Rhodophyta). II. Acrochaete heteroclada sp. nov., A. operculata sp. nov., and Phaeophila dendroides (Chlorophyta). Journal of Phycology 24: 528–539. http://dx.doi.org/10.1111/j.1529-8817.1988.tb04258.x

 

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Filed under Algae, Botany, Disease, Friday Fellow, Parasites