Fig. 7

The profile of the cellular microbiome in human brain. (A) Schematic of the relative representation of microbes in normal brain (cortex): overall readcounts from 17 independent brain samples (below) indicate that bacteria and fungi are the major species in brain. (B) Profiles of readcounts in 17 independent brain samples showing different patterns in different brain RNA-seq datasets (where B9 and B16 have distinctive patters) but overall conservation of the profile. Estimated abundances from the calculated numbers of rRNA per cell in the different organisms are as follows Archaea (10^-5 microbes per host cell), Bacteria (0.14), Chloroplastida (0.06, but type 2 contamination has not yet been excluded, Table 1), Amoebozoa (0.01), basal Eukaryota (0.01), Fungi (0.05), Holozoa (0.05, possibly because of cross-matching with Fungi, Figure 5B). Bacteria and Fungi represent 41% and 13% of the total burden (together >50%). (C) Signals that are present in >75% of all samples. (D) The brain has its own microbiome. (Lane 1) The mean brain microbiome profile from 17 independent samples. (Lane 2) The mean profile in tapwater. (Lane 3) Brain profile where all signals also detected in tapwater have been removed. (Lane 4) Mean skin microbiome profile. (Lane 5) Brain profile where all signals also detected in tapwater and skin have been removed, showing degradation of the signal. Although type 1 contamination cannot be formally excluded here, there may be overlaps between the brain and skin microbiomes (Discussion). However, despite attenuation of the signal, the subtraction demonstrates that there are microbial signals in brain that do not occur in skin. Panel (A) was created at Biorender.com