Ciliate feeding behaviour in a warm monomictic hyposaline lake with an anoxic hypolimnion: an experimental and vacuole content analysis approach

MACEK, M.; BAUTISTA-REYES, F.; FERMANI, P.; MARTÍNEZ-PÉREZ, M.E.

Armação dos Búzios, Rio de Janeiro, Brasil

Congreso; XIIIº International Congress of Protistology. XXVº Annual Meeting of the Brazilian Society of Protozoology. XXXVIº Annual Meeting on Basic Research in Chagas Disease; 2009

Resúmen: A ciliate assemblage structure, picoplankton feeding and growth in distinct layers was analysed in a high altitude, athalassohaline maar-crater lake Alchichica, Mexico (18o10?N; 93o10? W, altitude 2340 m). DAPI, Quantitative Protargol Staining and CARD-FISH protocols were used for ciliate counting, identification and estimation of food selection, respectively. Growth rates of ciliates were evaluated in fractionated samples, put in dialysis bags and exposed at different layers. Autotrophic picoplankton feeding peritrichs (mainly Pelagovorticella natans and Vorticella aqua-dulcis complex) and scuticociliates (Cyclidium glaucoma) often numerically dominated the ciliate assemblage; their growth was not significantly affected by the sample transplantation to a different layer. However, ciliates typical for well established thermocline/oxycline below 26 m, mixotrophic Euplotes cf. daidaleos and Pelagothrix sp., grew significantly  better being exposed at the upper metalimnion layer with considerable photosynthesis-active radiation (PAR) even though below 1 %. Among bacteria (EUB probe) found in ciliate vacuoles, significant feeding selection against Alfa-Proteobacteria (including genus Paracoccus) was proven typically in the oxycline (comparing to the water layer bacterial group composition), meanwhile in hypolimnion, supposing symbiotic sulphate-reducing bacteria (SBR) were observed in the present haptorids (Phialina sp., Pelagolacrymaria sp.). Archaea were observed in strictly anaerobic ciliates (e.g., Caenomorpha sp., Isocyclidium globosum) however, not dominating. Episymbionts of I. globosum have not been identified, yet, but they were stained with bacterial probe (EUB). Possible nucleus symbionts visualised in the samples should be studied in following research. Generally, a selective behaviour of ciliates was confirmed throughout the transition layer ? metalimnion - with both PAR and dissolved oxygen gradients; within the mixed water column, a selection was not apparent.