Article

Massive occurrence of heterotrophic filaments in acidified lakes: seasonal dynamics and composition

FEMS Microbiology Ecology (impact factor: 3.41). 01/2006; 46(3):281 - 294. DOI:10.1016/S0168-6496(03)00201-0 pp.281 - 294

ABSTRACT We documented permanent presence of heterotrophic filaments in three acidified lakes (pH<5) in the Bohemian Forest. Due to acidification, crustacean zooplankton were absent in all but one lake. In terms of carbon flow, microorganisms were thus almost exclusive players in the pelagic food webs. Variety of extremely long (>100 μm) heterotrophic filaments occurred in the lakes. The filaments usually accounted for >50% of total heterotrophic microbial biomass in the pelagic zone (medians of the total biomass: 82–108 μg C l−1), except for anoxic bottom layers and for episodic appearance of Daphnia longispina in one lake. Seasonal filament formation was mainly induced and maintained by grazing of mixotrophic flagellates (Dinobryon spp.) on small unicellular bacteria in the absence of cladoceran filtration. The filaments were less active than unicellular suspended bacteria. Fluorescence in situ hybridisation revealed that usually <50% of total bacteria were targeted with oligonucleotide probes for Eubacteria.

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Keywords

acidified lakes
 
anoxic bottom layers
 
Bohemian Forest
 
carbon flow
 
cladoceran filtration
 
Daphnia longispina
 
Dinobryon spp
 
heterotrophic filaments
 
lakes
 
mixotrophic flagellates
 
pelagic food webs
 
pelagic zone
 
situ hybridisation
 
small unicellular bacteria
 
terms
 
total biomass
 
total heterotrophic microbial biomass
 
unicellular