Fig. 7

Graphical summary of the current study. Left panel: In both HC and early-stage PD-RBD(−) compared to early-stage PD-RBD(+), the gut microbiome tends to favor degradation of dietary fibers over host mucin. In line with this, the abundance of fiber-associated bacteria (i.e., Prevotella, Faecalibacterium, and Agathobacter) is increased, whereas that of mucin degradation-associated bacteria (i.e., Akkermansia, Barnesiella, and Desulfovibrio) is decreased. In HC and PD-RBD(−), fiber-associated bacteria are associated with enhanced capability to discharge N-acetylglucosamine (GlcNAc) into the environment, which in turn suppresses biofilm formation by biofilm-producing bacteria (i.e., Escherichia). Right panel: Conversely, in early-stage PD-RBD(+) compared to both in HC and early-stage PD-RBD(−), the gut microbiome shows a preference for degrading host mucin over dietary fibers. Correspondingly, abundance of fiber-associated bacteria is reduced, and that of mucin degradation-associated bacteria is increased. The reduction in fiber-associated bacteria may lead to a scarcity of GlcNAc, thereby facilitating easier biofilm formation by bacteria. Consequently, these characteristics of PD-RBD(+) may be associated with increased susceptibility to infection and inflammation, potentially contributing to the exacerbation of PD pathophysiology, such as alpha-synuclein aggregation. PD Parkinson’s disease, RBD rapid eye movement sleep behavior disorder, HC healthy control. Created with BioRender.com