Parkinson’s disease: Desulfovibrio bacteria have been found guilty

In Parkinson’s disease, alpha-synuclein (alpha-syn) proteins are found to accumulate, in the form of Lewy bodies, in the brain, as well as in numerous other tissues and organs, including the spinal cord, autonomic nerves, myocardial tissue, and the human digestive tract. Some scientists suspect Desulfovibrio bacteria to be involved in the formation of these gut aggregates, which spread in a prion (sidenote: Prion Prions are infectious agents composed of proteins and are associated with specific types of neurodegenerative diseases. For example, bovine spongiform encephalopathy (BSE or “mad cow disease”) is a prion disease that affects cattle and whose human variant is Creutzfeldt-Jakob disease (CJD).

Source: https://www.who.int/fr/news-room/fact-sheets/detail/food-safety ) -like manner to the brain via the vagal nerve. Desulfovibrio appears with greater frequency and abundance in Parkinson’s patients, particularly in severe forms of the disease. Are these bacteria, which are known to produce hydrogen sulfide (H₂S), really capable of this? A Finnish study on animals attempted to find out, using a C. elegans nematode model expressing human alpha-syn.

10 patients, 10 spouses and nematodes

Three strains of Desulfovibrio (D. desulfuricans, D. fairfieldensis and D. piger) were isolated from the fecal samples of 10 Parkinson’s patients and their 10 healthy spouses at a clinic in Finland. These bacteria were then used to feed the nematodes. In parallel, other worms were fed Escherichia coli MC4100 that produces curli, an amyloid fiber that facilitates alpha-syn aggregation (positive control). A final group of worms were fed a diet containing E. coli LSR11, which is incapable of producing curli (negative control).

^{Sources (sidenote: https://www.who.int/news-room/fact-sheets/detail/parkinson-disease )}

An effect on brain aggregates

By studying head sections of the worms, it was found that all three strains of Desulfovibrio induced aggregates in the worms’ heads. Those taken from the stools of Parkinson’s patients seemed “more effective” than those taken from the healthy spouses: the worms displayed aggregates that were greater in number and size. Furthermore, worms fed with D. desulfuricans and, to a lesser extent, with D. fairfieldensis harbored significantly larger alpha-syn aggregates than worms fed with D. piger. 

An effect on mortality

In terms of survival, after four days, mortality was higher in the group of worms fed with Desulfovibrio from Parkinson’s patients. This increased mortality may be explained by the apparently greater virulence of the bacteria they received, making the bacteria more toxic and inducing more aggregates, at a level that became lethal. The authors believe that the greater virulence of the strains from Parkinson’s patients may relate to the greater or lesser capacity of Desulfovibrio to produce H₂S. Indeed, hydrogen sulfide may be involved in alpha-syn aggregation, facilitating the release of cytochrome c from mitochondria.