Prokaryotic picoplankton dynamics in a warm-monomictic saline lake: temporal and spatial variation in structure and composition

Abstract

The prokaryotic picoplankton (PPP) composition was studied in the tropical high-altitude saline Lake Alchichica, Mexico, using fluorescence in situ hybridization. Thetemporal dynamics of the PPP followed the annual hydrodynamics of this warm-monomictic lake. The abundance of both the autotrophic (APP) and heterotrophic(HPP) functional groups of PPP increased during the mixing period to reachmaximum values at the beginning of the stratification period, when the highesthybridization percentages for the domain Bacteria were also registered. The increasein PPP was most likely related to the availability of nutrients soon after the start ofthe mixing period. Throughout the rest of the stratification, APP and HPP decreasedsignificantly together with the hybridization percentages, mostly related to theexhaustion of nutrients in the mixing zone. In spite of being oligosaline, the prokar-yotic composition of Lake Alchichica was more typical of fresh than of saltier waterbodies. During the mixing period, the Pcy and Planctomycetes (PLA) formed the mainbacterioplankton fraction. Meanwhile throughout the stratification period PLA,Betaproteobacteria (BET) and Gammaproteobacteria (GAM) were the most abun-dant groups in the epilimnion and metalimnion. The domain Archaea (ARCH), BET,GAM, Paracoccus the principal denitrifier of the Alphaproteobacteria and sulphate-reducing bacteria were dominant in the oxycline and hypolimnion in associationwith dissolved oxygen depletion and the nutrient enrichment of the deeper strata.KEYWORDS: prokaryoplankton; warm-monomictic; oligosaline; tropical high-altitude