Principal component analysis (PCA) of selected physico-chemical parameters measured at each sampling site, representing the four spring clusters. PCA was performed on biofilm ( n = 39) samples, obtained between January 2018 and January 2019 and included the following environmental variables: Temperature, Ph, Na, Turbidity, TP, SO 4 , NO 3 -, and Fe. Size and transparency represent the log + 1 values of qPCR Legionella spp. levels. Loading scores and vectors are presented in Supplementary Table 6 and Supplementary Fig. 3 . The environmental variables were chosen following a PCA analysis from a larger subset of environmental factor (see Supplementary Fig. 2 and Supplementary Tables 4 and 5 ). THS = Tiberias Hot Springs. Significance level; * p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.001; **** p ≤ 0.0001
