Fig. 4

Average abundance versus occurrence plots (general AD-core and AD-transient microbiomes) for a bacterial and b archaeal OTUs. AD-core OTUs were defined as appearing in over 80% of the analysed sludge samples; AD-transient OTUs were defined as being present in less than 20% of the analysed samples. Density plots (orange bars) displayed below the graphs a and b represent the percentage of OTUs occurring in a specified number of samples. Community structural stability (Bray–Curtis dissimilarity) and membership (Jaccard dissimilarity) for AD-core and AD-transient populations of OTUs for c bacteria and d archaea (represented for bacterial and archaeal clusters). Values range from 0 (identical) to 1 (100% different). The boxes represent the interquartile range and the error bars show the 95% confidence intervals; cluster _aI (n = 33), _aII (n = 105), _aIII (n = 113), _bI (n = 23), _bII (n = 80), _bIII (n = 89), _bIV (n = 36), _bV (n = 34). Except for “WWTP-ADs” differences between the core and transient communities for the calculated indices were significant (Wilcoxon signed rank test with continuity; p < 0.05)