Microbial population dynamics and diversity during a bloom of the marine coccolithophorid Emiliania huxleyi (Haptophyta)

Abstract

Several previous studies have shown that Emiliania huxleyi blooms and terminations have been succeeded by an increase in large virus-like particles (LVLP), strongly suggesting the bloom collapse was caused by viral lysis. However, due to methodological limitations, knowledge of how such blooms affect the rest of the microbial community is limited. In the current study we induced a bloom of E. huxleyi in seawater enclosures and applied methods enabling us to describe the algae, bacteria and virus communities with greater resolution than has been done previously. The development of the dominating algal, viral and bacterial populations in the nutrient-amended seawater enclosures was followed by flow cytometry (FCM). Light microscopy (LM), PCR-denaturing gradient gel electrophoresis (PCR-DGGE) and pulsed-field gel electrophoresis (PFGE) were used to describe the changes in community composition in greater detail. The algal community was dominated by E. huxleyi until termination of the bloom by viral lysis. After bloom termination the additional algal populations present in the enclosures increased in abundance. A marked increase in viruses other than the one infecting E. huxleyi was also observed. Total bacterial number and community composition were also greatly influenced by the bloom and its collapse. KEY WORDS: Diversity · Emiliania huxleyi · Microbial community · Viral lysisResale or republication not permitted without written consent of the publisher

Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel

“…It had switched from E. huxleyi domination (Station 1) to a mixture of autotrophic dino£agellates (550 mm), nanophytoplankton, cryptophytes and picoeukaryotes, whose concentrations were all higher inside the high re£ectance area suggesting that virus-induced E. huxleyi lysis had triggered a rapid succession of the phytoplankton community. Castberg et al (2001) reached a similar conclusion using Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom W.H. Wilson et al 375 molecular methods (denaturing gradient gel electrophoresis) where they demonstrated that a new eukaryote community developed following the virus-induced demise of an E. huxleyi bloom during a seawater mesocosm experiment.…”

“…Although such conclusions from similar data sets are not new (Bratbak et al, 1993Brussaard et al, 1996;Castberg et al, 2001), there have been no reports of E. huxleyi-speci¢c viruses being isolated and maintained in culture from E. huxleyi blooms. Bratbak et al (1996) reported the initial isolation of a virus by plaque assay, however they were unable to propagate it further for characterization.…”

“…This further supports the prediction made by Wilson et al (in press) who discussed that viruses would play a much more important role towards the end of a bloom when virus concentrations would reach a threshold level required to cause termination of that bloom. Indeed, numerous mesocosm studies have been conducted where high concentrations of LVLPs have been observed following the demise of the E. huxleyi population (Bratbak et al, 1993;Castberg et al, 2001). It is di¤cult to measure such termination at sea since it is not often logistically possible to be on a ship throughout the progression of a bloom.…”

Pilot study of an EST approach of the coccolithophorid Emiliania huxleyi during a virus infection

“…Several studies have investigated the role of viruses in controlling the bloom development of E. huxleyi (Bratbak et al, 1993, Brussaard et al, 1996, Castberg et al, 2001, Jaquet et al, 2002, Wilson et al, 1998, 2002a, 2002b. It became evident from these investigations that viruses are intrinsically linked to the decline of E. huxleyi blooms.…”

Abundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay

“…During the stationary phase, the cells are generally covered by several layers of coccoliths and the distal ones are released into the water column when new ones are produced (Paasche, 2002). This phase is often associated with the decay of the bloom, when high abundance of E. huxleyi coincides with those of viruses, enhancing viral infection and bloom termination (Catsberg et al, 2001;Jacquet et al, 2002). The persistence of coccolithophorid blooms after nutrient exhaustion is haphazard and patchy in natural environments.…”