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Fundamental role of Blastocystis in intestinal diseases questioned in new study

Human intestine with intestinal bacteria, 3D illustration

A new study published in Frontiers in Cellular and Infection Microbiology has found that Blastocystis is not a strict anaerobic organism; shedding further light on the role it plays in intestinal diseases such as irritable bowel syndrome.

Blastocystis is the most common eukaryotic microbe in the human gut and it is often found in patients suffering from intestinal disease. However, the prevalence of Blastocystis, combined with the fact that the parasite is genetically extremely diverse has led to much debate as to the role it plays in intestinal diseases such as irritable bowel syndrome.  It remains unclear if this parasite is the cause of disease or not.

The Human Gut Colonizer Blastocystis Respires Using Complex II and Alternative Oxidase to Buffer Transient Oxygen Fluctuations in the Gut

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Blastocystis has long been considered an anaerobic organism, meaning that it does not require oxygen for growth and may react negatively or even die if oxygen is present. In a healthy gut the oxygen concentration is normally extremely low. In people suffering from intestinal disease, the disease often leads to a dysbiosis causing oxygen levels to increase. If Blastocystis was a strict anaerobic organism it would be unlikely to survive in such conditions, and yet it can.

A previous study by the same authors found that Blastocystis contains a gene for alternative oxidase. Their latest study, published in Frontiers in Cellular and Infection Microbiology, elaborates further on this hypothesis to suggest that this enzyme is the reason why this microbe can survive under conditions when oxygen concentration in the gut is rising.

The authors tested the cells in a respirometer in the presence and absence of alternative oxidase inhibitors. The results showed that Blastocystis cells themselves consume oxygen via this alternative oxidase. Thereby casting doubt on its strict anaerobic nature.

These findings provide important insight as to why there has been so much contradiction in determining the role Blastocystis plays in intestinal disease. Blastocystis may be found in people dealing with the initial phases of irritable bowel syndrome as alternative oxidase is able to buffer the oxygen levels for the organism, but it is not found in more severally inflamed guts simply because the oxygen levels are too high for Blastocystis to survive.

Lead author, Dr Mark van der Giezen from the University of Exeter says, “This research has shown, in contrast to previous assertions, that the intestinal microbial eukaryote Blastocystis is not a strict anaerobe but is able to deal with molecular oxygen. This might also be relevant for its controversial role in disease as it might explain its relation with intestinal disease such as irritable bowel syndrome that result in a dysbiosis of the gut with increased oxygen concentrations.”

Understanding the biology and the biochemistry of this enzyme will be extremely important for the development of different chemotherapy treatments. Crucial to the interpretation of future studies, Dr Mark van der Giezen says research “should indicate the severity of the inflammation in coming studies that aim to find a link between Blastocystis and such diseases”. 

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