Fig. 4

a PCA analysis of select process parameters whose identities are indicated by the red text and b NMDS ordination of microbial community composition in each sample based on Bray–Curtis distances calculated from ASV abundances. The variation explained by the first two principal components is indicated in the axis labels (a) and the stress for the NMDS ordination is indicated by the text in (b). Samples are coloured by phase of reactor operation while samples from the control reactor are distinguished from those from the hydrogen-supplemented reactor by symbol shape as indicated in the legend at the bottom of the figure. Samples with less than 1000 sequences were omitted from the NMDS ordination (b)