Spatial and temporal investigation of the microbial communities within laboratory scale biologically active carbon filters.

Laboratory scale Biologically Activated Carbon (BAC) filters were operated to unravel a high-resolution, spatial and temporal profile of microbial community dynamics from start-up to six months operation. Microbial biomass and richness increased over time (biomass 1.0x1012 ±8x1010 to 3.3x1012 ±4x1011 cells/biofilter, richness 367.3 ±125.4 to 538.8 ±148.1 between days 34 and 162). However, temporal increases were not directly linear, instead characterised by periods of overall growth and decay. Growth was highest between days 34 and 62 with a 3.92-fold increase from the initial 34 days. Depth and time were significant drivers of variance (24% and 15%, p < 0.001), though 79% of biomass was located in the top 15cm, dominated by a stochastically assembled group of primary colonisers (e.g. Beggiatoaceae 51.2 ±12% over all time points). Differential abundance analysis confirmed that the dominant primary colonisers did not significantly change in absolute number over time, however maintained their relative abundance. Instead changes in biomass were driven by rare deterministically selected taxa (e.g. BSV26 of order Kryptoniales -14.4 log fold increase between days 34 and 162), dynamically changing over time. Demonstrating that changes in biomass and diversity are driven by rare taxa around a generally stable and unchanging core of primary colonisers seeded from the influent water.