Prokaryotic Dynamics in the Meromictic Coastal Lake Faro (Sicily, Italy)

Carmela Raffa,Angelina Lo Giudice,Luigi Michaud,Marc Strous,Carmen Rizzo,Emilio De Domenico,Marilena Sanfilippo

doi:10.3390/d11030037

Abstract

Lake Faro, in the North-Eastern corner of Sicily (Italy), shows the typical stratification of a meromictic tempered basin, with a clear identification of the mixolimnion and the monimolimnion, separated by an interfacial chemocline. In this study, an annual-scaled study on the space-time distribution of the microbial communities in water samples of Lake Faro was performed by both ARISA (Amplified Ribosomal Intergenic Spacer Analysis) and CARD-FISH (Catalyzed Reporter Deposition-Fluorescence In Situ Hybridization) approaches. A correlation between microbial parameters and both environmental variables (i.e., temperature, pH, dissolved oxygen, redox potential, salinity, chlorophyll-a) and mixing conditions was highlighted, with an evident seasonal variability. The most significative differences were detected by ARISA between the mixolimnion and the monimolimnion, and between Spring and Autumn, by considering layer and season as a factor, respectively.

Highlights

Among ecosystems of scientific interest, meromictic lakes represent complex and quite rare systems with peculiar characteristics that make them optimal candidates as study models in microbial ecology
Oxic and anoxic layers of Lake Faro differed in several hydrological parameters
Dissolved oxygen (Figure 2a) and redox potential (Figure 2b) profiles showed that the interface between oxic and anoxic layers was located at a depth ranging from 12 to 24 m in the period between March and December

Summary

Introduction

Among ecosystems of scientific interest, meromictic lakes represent complex and quite rare systems with peculiar characteristics that make them optimal candidates as study models in microbial ecology. Meromictic lakes are characterized by a stratification of the water column into an upper oxygenic layer (namely the mixolimnion), a bottom anoxygenic layer (namely the monimolimnion), and a transition zone, the chemocline, that separates the former zones [1,2,3]. The metabolic diversity of prokaryotes allows the exploitation of the entire chemical gradient of the water column [7], with huge blooms that often occur around the chemocline [8]. This latter represents a barrier for microbial dispersion as it separates different functional microbial groups [9]. Cyanobacteria are abundant in oxic layers [4,10], anaerobic phototrophic bacteria are generally associated with the chemocline, and sulfur bacteria can predominate within anoxic layers [11,12,13]

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