Ciliated protozoa from an industrial activated sludge WWTP: a survey on the biodiversity combined with an integrative taxonomy study on retrieved species

Starting from December 2018 and for a period of one year, we investigated the species composition of ciliate community in the industrial WWTP Cuoiodepur (San Romano, Pisa, Italy). The biological section of this plant is constituted by a predenitrification (anoxic) tank and a nitrification-oxidation tank with an internal recirculation of 10 times the influent flow rate. The main aim of this study was to start exploring and providing information on the ciliate biodiversity and community dynamic change in this peculiar man-made environment, through the application of an integrative taxonomy study on the retrieved species plus a semiquantitative counting way. Main results and conclusions were summarized below. (1) A total of 21 ciliate species (belonging to 7 out of 11 classes of the Phylum Ciliophora) have been identified in the biological process of studied WWTP. Among them, 16 retrieved species were observed on the sampling day, present in both nitrification and denitrification tanks, which shows the capability to survive the short oxic/anoxic cycling typical of the studied WWTP process. (2) Aspidisca cicada, Euplotes spp., Paramecium calkinsi, Phialina n. sp., and Holophrya teres were five representative species in Cuoiodepur with highest rate of discovery, and the plant shows some peculiarities as possessing some rarely recorded taxa, like Bakuella subtropica, Phialina n. sp., Thuricola similis, Trochiliopsis australis, and Zosterodasys debilis. (3) Throughout the investigation period, the overall composition of the ciliate community in the habitat was basically stable, as most retrieved species showed high rate of occurrences and a stable proportion of the three functional groups consisting the ciliate community. (4) This research provided a significant contribution to the knowledge in the field of taxonomy and systematics of ciliates, i.e., a) the discovery and characterization of two ciliate species new to science, namely Euplotes n. sp. and Phialina n. sp.; b) the redescription and revised diagnosis of six poorly known species, namely Euplotes corsica, H. teres, Oxytricha similis, Podophrya libera, T. similis, and Z. debilis;