DISREGARDED DIVERSITY AND ECOLOGICAL POTENTIALS Review Article

Perkinsozoa, a well-known marine protozoan flagellateparasite group, newly identified in lacustrine systems:a review

Jean-Francois Mangot • Didier Debroas •

Isabelle Domaizon

Received: 19 August 2009 / Accepted: 12 April 2010 / Published online: 16 May 2010

� Springer Science+Business Media B.V. 2010

Abstract The recurrent detection of parasitic zoo-

spores among aquatic heterotrophic flagellates (HFs)

has recently modified our view of how the microbial

loop is organized, and called into question the role of

eukaryotic parasites in the aquatic trophic food web.

The Perkinsozoa group, already known to play a

significant role as parasite in marine systems, is of

special interest here, since it has recently been

detected in several lakes by constructing clone

libraries. In marine systems, this group is known to

consist solely of intracellular parasites of molluscs or

phytoplanktonic species, but their hosts in freshwater

environments are still unknown, and little is yet

known about their functional importance in plank-

tonic systems. This review summarizes the main

information currently available about Perkinsozoa

through a description of their phylogenetic position,

their life cycles, and regulatory factors, and the

consideration of the specificities of their hosts in

marine systems, and the few data recently acquired in

lakes.

Keywords Perkinsozoa � Eukaryotic parasites �Marine and lacustrine systems

Introduction

Numerous molecular studies have recently character-

ized picoplanktonic assemblages by amplifying and

sequencing the gene coding for 18S rRNA gene, both

in marine and freshwater systems (Dıez et al., 2001;

Moreira & Lopez-Garcıa, 2002; Lefranc et al., 2005;

Lepere et al., 2006, 2008; Lefevre et al., 2008). These

data have called into question the role of eukaryotic

parasites in aquatic systems. More precisely, the

importance of putative parasites within small eukary-

otes has made it clear that the concept of a microbial

loop within which heterotrophic flagellates (HFs)

being thought to be mainly bacterivorous (Azam

et al., 1983; Sanders et al., 1989) does not adequately

describe the various interactions within the microbial

food web. The presence of parasitic zoospores among

HFs has led us to envisage greater taxonomic and

functional heterogeneity among these heterotrophs,

Guest editors: T. Sime-Ngando & N. Niquil / Disregarded

Microbial Diversity and Ecological Potentials in Aquatic

Systems

J.-F. Mangot (&) � I. Domaizon

INRA – UMR 42 CARRTEL, Centre Alpin de Recherche

sur les Reseaux Trophiques des Ecosystemes Limniques,

Thonon-les-bains Cedex 74203, France

e-mail: jean-francois.mangot@wanadoo.fr

J.-F. Mangot � D. Debroas

LMGE, Laboratoire ‘‘Microorganismes: Genome &

Environnement’’, UMR CNRS 6023, Campus des

Cezeaux, 24, av. des Landais, Aubiere Cedex 63177,

France

123

Hydrobiologia (2011) 659:37–48

DOI 10.1007/s10750-010-0268-x

particularly if parasitism is taken into account.

Parasitism is indeed a model of interaction, which

increases the complexity of the trophic network by

extending food chains, increasing connectance, and

the efficiency of transfers; particularly as these

parasites have relatively complex life cycles, and

are known to infect organisms of various trophic

levels (Arias-Gonzales & Morand, 2006).

Most aquatic organisms are known to contain

intracellular symbionts (viruses, archaea, bacteria,

fungi, and other eukaryotes parasites) (Canter &

Lund, 1969; Cole, 1982; Embley et al., 1992;

Holfeld, 1998; Erard-Le Denn et al., 2000; Brussaard,

2004; Park et al., 2004). Also, while viral parasitism

on bacterioplankton in aquatic systems has been well

documented for the last 10 years (Fuhrman, 1999;

Wommack & Colwell, 2000; Bettarel et al., 2003,

2004; Weinbauer, 2004), studies focusing on eukary-

otic parasites have generally been overlooked. Prob-

ably because little is yet known about the identity and

diversity of these parasites in aquatic systems,

eukaryotic parasitism is often poorly taken into

account in functional models (Arias-Gonzales &

Morand, 2006; Lafferty et al., 2006). However, some

significant regulating effects have been reported in

the literature, and have highlighted the significant

impact of parasitism on algal community control in

marine systems (Johansson & Coats, 2002; Park

et al., 2002; Ibelings et al., 2004; Kagami et al., 2004,

2010). For instance, Syndiniales parasites are able to

infect marine dinoflagellates, which are responsible

for toxic red tides, also known as harmful algal

blooms (HAB), which can cause illness and even

human death (Zingone & Enevoldsen, 2000). Cham-

bouvet et al. (2008) recently revealed that the dino-

flagellate parasitoid successions in a natural estuary

are correlated to the rapid development of four major

species of phytoplanktonic dinoflagellate populations

(Heterocapsa rotundata, Scrippsiella trochoidea,

Alexandrium minutum, and Heterocapsa triquetra).

On the basis of such examples, it is obvious that

planktonic food web models must now take the role

of eukaryotic parasites into account (Arias-Gonzales

& Morand, 2006; Lafferty et al., 2006, 2008).

Parasitic interactions increase the complexity of the

trophic network both through direct effects (host–cell

mortality, parasitic zoospores used as a resource by

grazers) and indirect impacts (cascade effects on the

competition between phytoplanktonic species, and on

the redistribution and recycling of organic matter

after cell lysis) that modify connectance and the

efficiency of transfers (Kagami et al., 2004, 2010;

Arias-Gonzales & Morand, 2006).

In aquatic ecosystems, three major eukaryotic

lineages are known to include potentially parasitic

organisms. Organisms belonging to the fungal group

of Chytridiomycota are known mainly as eukaryotic

parasites of phytoplankton (Goldstein, 1960; Canter

& Lund, 1969; Ibelings et al., 2004). Some para-

sites have also been reported within the Cercozoa

(Rhizaria phyla), in which a handful of taxa are

parasites of diatoms (Cavalier-Smith & Chao, 2003).

However, alveolates exhibit the most considerable

diversity of known eukaryotic parasites, including

various morphologically distinctive parasites among

the three traditional phyla of Ciliophora, Dinoflagel-

lata, and Apicomplexa (Cavalier-Smith, 1993) and

the newly included Chromerida (Moore et al., 2008;

Obornık et al., 2009). Parasitic activities of alveolates

have been reported in a wide range of ecosystems

(soil, aquatic, etc.). In order to begin with, apicom-

plexans (ex-sporozoan) and ciliates are major para-

sites of marine and terrestrial populations

(crustaceans, fish, or mammals), and can cause

extensive health and economic damage to human

populations, particularly those in the developing

world (Hakimi & Deitsch, 2007). Leaving aside

these two alveolates phyla, Dinoflagellata constitute

the main source of aquatic parasites (Blastodiniales,

Syndiniales). Among them, Syndiniales constitute an

atypical order of dinoflagellates, consisting of well-

known and exclusively marine parasites (Hematodi-

nium spp., Amoebophrya spp.), which display a host-

specific infection strategy (Groisillier et al., 2006;

Chambouvet et al., 2008; Guillou et al., 2008).

Finally, Chromera velia, a newly cultured photosyn-

thetic symbiont of the stony coral Plesiastrea purpu-

rea, constitutes the latest symbiotic alveolates defined

until now (Moore et al., 2008). Based on the available

sequences, chromerids may form a sister group to the

parasitic apicomplexans and predatory colpodellids

rather than the photoautotrophic dinoflagellates

(Moore et al., 2008; Obornık et al., 2009), and its

discovery allows to speculate on the origin of

symbiosis and parasitism among the Alveolata.

The Perkinsozoa group, a sister-group of the

dinoflagellates (also known as perkinsids or perkins-

eans), is structured around two well-known marine

38 Hydrobiologia (2011) 659:37–48

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parasites, Perkinsus marinus (Mackin et al., 1950)

and Parvilucifera infectans (Noren et al., 1999)

(Fig. 1). Perkinsids are intracellular parasites that

form a relatively close sister lineage to generally free-

living dinoflagellates (Noren et al., 1999; Leander &

Keeling, 2003). Little is known about Perkinsozoa

diversity, especially in freshwater, and this consti-

tutes a real handicap for attempts to understand the

role of parasites in aquatic systems more precisely.

Since the middle of the 2000s, based on recent

descriptive studies (Lefranc et al., 2005; Richards

et al., 2005; Lefevre et al., 2007; Lepere et al., 2008)

attempts have been made to characterize the compo-

sition of the picoeukaryotic population (\5 lm) in

several lakes using cloning–sequencing approaches.

The recurrent detection of sequences of putative

parasites in these studies explains the new interest in

this group of eukaryotic parasites in lacustrine

systems where their presence had hitherto been

unknown. We propose to review the main informa-

tion available about this phylogenetic group in both

marine and freshwater systems.

The phylogenetic position of Perkinsozoa phyla

among the lineage of alveolates

Perkinsids have mainly been studied in marine

environments (Mackin et al., 1950; Noren et al.,

1999; Park et al., 2002, 2004, 2006; Casas et al.,

Fig. 1 Phylogenetic tree showing the position of each clades

of Perkinsozoa among the alveolates based on their small

subunit ribosomal RNA (SSU rRNA) sequences. The names of

the lakes in which sequences were identified are indicated with

their access number. Numbers at branch nodes indicate

significant bootstrap confidence values in percent (BV

[90%). The tree was constructed (maximum parsimony

criteria), and the BVs for terminal nodes were calculated both

using the ARB software package (Ludwig et al., 2004)

Hydrobiologia (2011) 659:37–48 39

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2008). Although there is now strong evidence that

perkinsozoans constitute a sister group of dinoflagel-

lates (Moore et al., 2008), their systematic position

has long been controversial. They have been alterna-

tively linked to Apicomplexa or to Dinoflagellata

(Coss et al., 2001; Brugerolle, 2002). Initially, the

classification of organisms within this genus was

based on a variety of morphological criteria, espe-

cially at the ultrastructural scale. The debate about

their phylogenetic position is illustrated by the

example of Perkinsus marinus, the best-known

parasite in this group. Initially described as a fungus

named Dermocystidium marinus by Mackin et al.

(1950), on the basis of the observation of the position

of the nucleus close to the cell wall and the presence

of a centrally located endosome, a subsequent

reexamination of its morphological features led to

its being transferred to the protozoan phylum Laby-

rinthomorpha, and designated as Labyrinthomixa

marina (Mackin & Ray, 1966). The evaluation of

zoospore ultrastructure by Levine (1978) led to a

further reconsideration of the phylogenetic position

of Perkinsus marinus and the establishment of a new

Perkinsean taxon in the protozoan phylum Apicom-

plexa. Indeed, zoospores of this species differ from

those of all other apicomplexans in having a mastig-

oneme-bearing anterior flagellum, and having an

atypical conoid apparatus on the apical complex

structure. More recently, studies based on morpho-

logical observations and phylogenetic analyses of

alveolate DNA sequences, and especially actin gene

sequences (Reece et al., 1997; Siddall et al., 1997),

led to their exclusion from the phylum Apicomplexa,

and the conclusion that Perkinsus was related to the

dinoflagellates. However, on the basis of ultrastruc-

tural features and phylogenetic studies of the 18S

rRNA sequence of a new parasitic species, Parvilu-

cifera infectans, Noren et al. (1999) established a new

phylum, Perkinsozoa, within the Alveolata. However,

the apparent widespread serological affinity between

Perkinsus marinus and diverse parasitic dinoflagel-

lates suggested a closer phylogenetic link to the

syndinean dinoflagellate lineage (Bushek et al.,

2002). This newly established phylum is assumed to

be entirely parasitic (Moreira & Lopez-Garcıa, 2002),

and it consists of two freshwater clades as defined by

Lepere et al. (2008) by applying the criteria of Zwart

et al. (2002). According to these authors, an envi-

ronmental clade comprises at least two sequences that

are at least 95% identical and originate from at least

two different aquatic sites. Thus, we have defined two

clades inside the phylum of Perkinsozoa (named

clade 1 and clade 2), each structured around two

marine species of parasites, Perkinsus marinus (par-

asite of molluscs) and Parvilucifera infectans (para-

site of dinoflagellates) (Fig. 1). Indeed, in order to

determine the phylogenetic affiliation of perkinsozo-

an species reported here with other congeneric

species, a phylogenetic analysis thanks to ARB

software was performed (Ludwig et al., 2004). The

rooted tree identified two clades highly supported by

bootstrap value (BV) of 99% (Fig. 1). Among the

second clade of Perkinsozoa named clade 2, Parvilu-

cifera infectans with other environmental sequences

reported here constituted a higher-order clade with a

strong BV (98%). Perkinsus marinus, often consid-

ered as part of the Perkinsozoa clade 1, seems to form

only an additional branch apart of this clade which is

constituted by environmental sequences supported by

a strong BV (100%).

Perkinsozoa in marine systems: a natural cause

of diseases in oyster cultures and of toxic

dinoflagellate proliferations

Perkinsus spp. are known to be parasites of molluscs.

These hosts are easily sampled in situ, moreover,

problems involving infected molluscs have an eco-

nomic impact as many of these species are commer-

cialized; consequently Perkinsus spp. are the most

studied perkinsozoan species. Recently, an assay tool

based on a polymerase chain reaction coupled with

restriction fragment length polymorphism (PCR–

RFLP) of the rRNA internal-transcribed spacers (ITS

region) has made it possible to target these parasites.

This methodology was validated to discriminate

between the various Perkinsus species (P. marinus,

P. olseni, P. mediterraneus, and P. chesapeaki), to

provide rapid identification, and the final goal was to

prevent recurrent diseases (Abollo et al., 2006).

Perkinsus marinus is a well-known agent of the

disease known as ‘‘Dermo’’, which is the main cause

of mortality of bivalve molluscs in American coastal

waters. The eastern oyster, Crassostrea virginica, and

the Pacific oyster, Crassostrea cortenziensis, are both

parasited by Perkinsus marinus, along the Gulf of

Mexico and Atlantic coast of North America

40 Hydrobiologia (2011) 659:37–48

123

(Burreson et al., 1994; Soniat, 1996), and along the

Pacific coast of Mexico, respectively (Caceres-Martı-

nez et al., 2008). In European coastal waters, some

species of the Perkinsus genus are also able to infect

other bivalve hosts. This is the case of Perkinsus

mediterraneus, a parasite of the European flat oyster

Ostrea edulis (Casas et al., 2008), and P. atlanticus, a

parasite of the Portuguese clam Ruditapes decussatus

(Azevedo, 1989; Ordas & Figueras, 1998).

As illustrated by these examples, Perkinsus spe-

cies are very widely geographically distributed,

which partly reflects their host distribution (Fig. 2).

It seems that a variety of levels of host specificities

can be observed. Perkinsus marinus seems to solely

infect the oyster Crassostrea, while, the clam Rudi-

tapes decussatus known to be infected by P. atlan-

ticus in European waters can also be parasited by P.

qugwadi on the west coast of Canada (Blackbourn

et al., 1998).

Most of the Perkinsus spp. seem to be specific to

one type of bivalve (clams or oysters); however,

some of them are able to infect various types of host,

such as Perkinsus olseni which is a parasite of both

clams and abalones. Depending on its geographic

location, P. olseni, which is known to infect the

Spanish Ruditapes decussatus in Mediterranean

waters (Elandaloussi et al., 2009), elsewhere also

infects the Korean Venus clam Protothaca jedoensis

(Park et al., 2006) and the Australian abalone species,

Haliotis rubra and Haliotis laevigata (Lester et al.,

1990). Perkinsid infection of species other than

molluscs has been reported with the case of

P. chabelardi, a parasite of sardine eggs (Gestal

et al., 2006). The prevalence of P. marinus, P.

atlanticus, and P. olseni on their respective hosts are

highly variable, and can sometimes reach very high

values (up to 100%) (Burreson et al., 1994; Ngo &

Choi, 2004). Seasonal variations have been reported

by several authors (Ngo & Choi, 2004; Gullian-

Klanian et al., 2008); these changes in prevalence are

linked to various environmental factors (temperature,

salinity, phosphorous, silica variations, etc.).

The Perkinsozoa group also includes various

parasites of protistan species. Parvilucifera infectans

is known to infect 26 different microalgal species, 17

of which belong to 10 different dinoflagellate genera

(Park et al., 2004). The distribution of this parasite

extends from Australian to Norwegian seas, where

they commonly infect photosynthetic and heterotro-

phic dinoflagellates (Park et al., 2004) (Fig. 2).

Although the rare mortality rates estimated until

now were low (\0.2% of the host population per day,

Park et al. 2004), several authors suggest that

Parvilucifera infectans could have a significant

regulatory effect on its host, contributing to bloom

dissipation and controlling dinoflagellate populations

(Gisselson et al., 2002; Park et al., 2004).

Other species phylogenetically close to P infectans

have recently been isolated and studied. They include

Parvilucifera sinerae sp. nov., a perkinsid isolated

from a bloom of the toxic dinoflagellate Alexandrium

minutum in Mediterranean Sea (Figueroa et al.,

Fig. 2 Global distribution

of Perkinsus spp. (whiteellipsoidal symbol) and of

Parvilucifera spp. (grayellipsoidal symbol). Each

symbol notes locations

where infections have been

observed in molluscs or

phytoplanktonic organisms

Hydrobiologia (2011) 659:37–48 41

123

2008), and Parvilucifera prorocentri sp. nov., a novel

parasite found to infect the marine benthic dinofla-

gellate Prorocentrum fukuyoi (Leander & Hoppen-

rath, 2008). The pathogenicity of Perkinsus spp. has

been relatively thoroughly investigated and quanti-

fied, but this is not the case for Parvilucifera

spp. which constitute a newly described group of

parasites for which no quantitative prevalence data

are available.

Life cycle and regulatory factors of Perkinsozoa

phyla in aquatic systems

The life cycles of the three genera of perkinsids,

Perkinsus spp., Parvilucifera spp., and Cryptophagus

spp., display some common characteristics. For

instance, like chytrids, perkinsids have a free living

stage (a zoosporic flagellate) during their life cycle

(Figs. 3, 4). This infectious stage is characterized by

the presence of two flagella on the apical complex,

reminiscent of Apicomplexa (Fig. 5). The first steps

in the infection process have been studied in detail in

the case of Perkinsus spp., a parasite of molluscs, but

are less known for its two sister genera Parvilucifera

spp. and Cryptophagus spp. After the phagocyting of

Perkinsus trophozoites by host hemocytes (Fernan-

dez-Robledo et al., 2008), a pale appearance of the

digestive gland was observed, the mantle was

retracted, gonad development inhibited, growth

retarded, and eventually the hosts died (Mackin,

Fig. 3 Negative staining of the zoospore of Perkinsus sp.

isolated from Macoma balthica. Scale bar = 2 lm (from Coss

et al., 2001, p. 49) (� by the Society of Protozoologists, 2001.

With permission from Wiley-Blackwell)

Fig. 4 Free-living stage of Perkinsozoa clade 1 hybridized by

TSA–FISH (probe: PERKIN_01) observed by epifluorescence

microscopy. Scale bar = 10 lm

Fig. 5 Ultrastructure section of Perkinsus atlanticus zoospore,

showing the nucleus (N), mitochondrion (M), the plastid

(arrow), and the apical end (*) containing such apical complex

elements as rhoptries (R). Near the zoospores, some transverse

section of the flagella (F) Scale bar = 0.5 lm (from Teles-

Grilo et al., 2007, p. 164) (� Elsevier GmbH, 2007. With

permission from Elsevier Science)

42 Hydrobiologia (2011) 659:37–48

123

1951). The rest of the life cycle of Perkinsozoa shows

some similarities among the three genera, such as the

presence of a similar intracellular stage, the trophont.

Perkinsus spp. and Parvilucifera spp. trophonts

secrete a ‘‘sporangium’’ inside the host cell, within

which the sporozoites differentiate (Noren et al.,

1999; Coss et al., 2001), whereas Cryptophagus spp.

zoospores grow and directly divide within the host

cytoplasm and are not surrounded by a sporangium or

a cyst envelope (Brugerolle, 2002). Thanks to these

studies, a general life cycle scenario of perkinsids

parasites can now be proposed: After the adhesion of

the sporozoite to the host cell surface, the zoospore

penetrates into the host cytoplasm. The trophont then

grows within the host cytoplasm, and undergoes

multiple divisions either in sporangia (Perkinsus spp.

and Parvilucifera spp.) or within the host cytoplasm

(Cryptophagus spp.). After 4–5 successive nuclear

mitoses by schizogony, trophozoite/sporozoite differ-

entiation occurs, and buds onto the host cell surface

(Fig. 6). Sporozoites acquire flagella, micronemes

and other apical structures, and are then release

outside the host structure. Sometimes, a resting cyst-

like stage can occur during the trophozoite stage.

It seems likely that the development of populations

of Perkinsozoa parasites could be controlled by

various abiotic factors, notably temperature. Indeed,

the proliferation of all the Perkinsus species is

correlated with warm summer water temperatures

(above 20�C), which is when pathogenicity and the

associated mortality are the highest (Soudant et al.,

2005). The same authors report a slight, but signif-

icant, decrease in the percentage of viable cells

(PVC) after cold or heat treatments (-80, -20, and

40�C). Furthermore, temperature may have also an

impact on the development of the hosts of Perkinsus.

The gonadal development of Ruditapes philippina-

rum appeared to be more efficient at higher temper-

ature (18�C, Delgado & Camacho, 2007). As a result,

temperature may have direct and indirect effects, on

the viability of Perkinsozoa species and the metab-

olism of their hosts, respectively. However, some of

them are more tolerant to variations in various

environmental factors. P. atlanticus is able to adapt

to very different culture media, salinity, and temper-

ature conditions, and its development seems to be

independent of density (Ordas & Figueras, 1998).

Detection and recent interest in the Perkinsozoa

phylum in lacustrine systems

The characterization of small-eukaryote diversity

(\5 lm) conducted in various lakes with differing

trophic status (Lefranc et al., 2005) has recently

revealed the presence of Perkinsozoa in freshwater

systems. This study showed that sequences affiliated to

Perkinsozoa can account for up to 60% of the clone

library (18S rRNA gene) obtained from the eutrophic

lake Aydat (summer sampling in the euphotic zone).

The sequences obtained for this lake were affiliated

with low similarities (86–90%) to Perkinsus marinus.

The unexpected qualitative importance of perkinsids

in lacustrine systems led to the emergence of numer-

ous questions about their functional roles in lacustrine

food webs. Several recent studies also dealing with the

Fig. 6 Light micrograph of the different live stages of cultured

Perkinsus mediterraneus cells in JL-ODRP-2F medium.

Trophozoites (T) showing a granular cytoplasm with a large

vacuole (v) and a prominent vacuoplast (vp). Perkinsusmediterraneus divides by schizogony, and schizonts (S) vary

in size. Scale bar: 20 lm (from Casas et al., 2008, p. 37) (� by

the International Society of Protistologists, 2008. With

permission from Wiley-Blackwell)

Hydrobiologia (2011) 659:37–48 43

123

characterization of lacustrine picoeukaryotic diversity

have confirmed the recurrent presence and importance

of this group. Perkinsozoa have been detected in two

geographically distinct, oligotrophic lakes, the Amer-

ican Lake George (euphotic zone) (Richards et al.,

2005) and the French Lake Pavin, respectively (oxic

and oxycline zones) (Lefevre et al., 2007, 2008). More

recently, Lepere et al. (2008) have reported their

presence in the 18S rRNA gene library of perkinsids

sequences in the epilimnion of Lake Bourget in spring

and summer, providing semi-quantitative information

about this group. In this mesotrophic system,

sequences of Perkinsozoa account for 15.2% of the

different OTUs obtained during the summer (August)

(29.2% of the clones), whereas in May, the proportion

was only about 5% of both sequences and clones. All

these perkinsid sequences obtained from sequencing in

various lacustrine systems can be divided to form two

clades of Perkinsozoa (named clade 1 and clade 2).

Recently, on the basis of these molecular data, specific

oligonucleotide probes have been designed to target

each clade of Perkinsozoa to quantify and estimate the

in situ dynamics of this group in Lake Bourget

(Mangot et al., 2009). The temporal dynamics of the

free-living stage (zoospore) of clade 1 and clade 2 of

Perkinsozoa (size fraction \5 lm), as analyzed by

epifluorescence microscopy and TSA-FISH (Fig. 4),

have all revealed an increase in abundance in summer

in the epilimnion of the Lake Bourget (up to 30% of all

eukaryotes targeted by the EUK1209R probe in July

and August), possibly corresponding to an infectious

peak. As already reported in marine systems (Soudant

et al., 2005), the dynamics of freshwater perkinsozo-

ans are strongly correlated to temperature (Lefranc

et al., 2005, Lefevre et al., 2007, 2008; Lepere et al.,

2008; Mangot et al., 2009). In Lake Bourget, the

dynamics of Perkinsozoa clade 1 coincide significantly

(RDA analysis, P \ 0.05) with the abundance pat-

terns of Peridinium and Ceratium (Dinoflagellates),

whereas the dynamics of Perkinsozoa clade 2 are

correlated to the presence of Dinobryon (Chrysophy-

ceae). Although some putative phytoplanktonic host–

Perkinsozoa links could be suggested on the basis of

this study, no definite association (host/parasite) was

demonstrated. Only one study has reported the pres-

ence of an algal-parasitic Perkinsozoa, Rastrimonas

subtilis gen. et sp. nov (Brugerolle, 2003) in freshwater

environments. This taxon was previously known as

Cryptophagus subtilis (Brugerolle, 2002), a parasite of

cryptophytes. The ultrastructure and life cycle of this

freshwater perkinsid have been studied using cultures

of the cryptophyte Chilomonas paramaecium, origi-

nally collected from a river. Because no genetic

characterization of this taxon was obtained by

sequencing, its affiliation to one of the two clades of

Perkinsozoa defined here is not possible. However, the

description of its ultrastructure given by Brugerolle

strongly supports the affiliation of R. subtilis to the

phylum of Perkinsozoa (Brugerolle, 2002).

Conclusion

It is now obvious that eukaryotic parasitism, hitherto

generally overlooked in aquatic studies, could in fact

play a critical role in the functioning of these

ecosystems. For instance, the Perkinsozoa, a sister-

group of dinoflagellates, are a good example of

organisms that have generally been classified as

unidentified HFs, but which could affect planktonic

populations. These parasites have mainly been stud-

ied in marine environments, where they constitute

one of the main causes of mortality in some molluscs

(oysters, clams, abalones, etc.) and phytoplanktonic

species (especially, dinoflagellates) worldwide. Valu-

able knowledge has been acquired about the role of

some Perkinsozoa in marine systems, but very little

information is known about this parasite group in

freshwater systems. It is only recently, thanks to the

development of molecular techniques, that Perkinso-

zoa has been detected and quantified in lakes. Some

tools are now available that can target these groups

(notably specific oligonucleotide probes), but further

research is now needed to connect the potential

quantitative importance of these parasites to their

precise functional roles in lacustrine systems, notably

through cell–scale approaches. Isolating infected

hosts, coupled with molecular analysis (genome

amplification) of these single cells could reveal the

association between lacustrine perkinsids and their

hosts. The use of double staining (host/parasite) using

TSA–FISH would, in a second step, provide some

essential information about prevalence and host/

parasite in situ dynamics. A combination of conven-

tional methods (isolation, microscopic observations)

and molecular techniques should soon help elucidate

questions such as the diversity of Perkinsozoa in

lacustrine systems, their real function, and the

44 Hydrobiologia (2011) 659:37–48

123

identity of their hosts in this system, or even make it

possible to draw a parallel between their roles in

marine and in freshwater systems.

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Author Biographies

Jean-Francois Mangot is

a PhD student in lacustrine

microbial ecology at Blaise

Pascal (Clermont-Ferrand)

and Savoie Universities,

France. His PhD thesis

deals with the study of the

dynamics and the diversity

of potential eukaryotic par-

asite microorganisms in

lacustrine systems, espe-

cially the group of Perkin-

sozoa recently discovered in

freshwater ecosystems.

Didier Debroas is Profes-

sor at Blaise Pascal Univer-

sity in the fields of microbial

ecology and bioinformatics.

He began his scientific

career by studying the

microbial ecology of the

rumen ecosystem and he has

been working since 1993 on

the aquatic ecosystem. At

present, he is the leader of

the group ‘‘Environmental

Microbiology and Bioinfor-

matics’’ at the LMGE lab

(CNRS, Aubiere – http://

www.lmge.univ-bpclermont.fr). Currently, his main research

concerns (i) the taxonomic and functional diversities of lacus-

trine picoplankton and (ii) the community genetic potential of

these microorganisms. His research group is developing (i) some

methodologies for analysing diversity and functions at the cell

level (cell-sorting, metagenomics, etc.) and (ii) bioinformatic

tools for dealing with data sequences originated from massive

parallel sequencing.

Hydrobiologia (2011) 659:37–48 47

123

Isabelle Domaizon is

researcher at the hydrobio-

logical INRA center (CARR-

TEL, Thonon, France). She is

currently the leader of the

group ‘Biodiversity Func-

tioning Evolution of Lacus-

trine Ecosystem’. Her major

research interest deals with

the structure and functioning

of microbial food webs in

lakes; the general objective is

to identify the links between

the structure of planktonic

communities and the func-

tioning of lacustrine pelagic systems. The specific research

questions addressed concern (i) the diversity of microbial

eukaryotes, (ii) the trophic interactions and pathways within

microbial trophic networks and up to higher trophic levels, and (iii)

the regulatory factors involved in the dynamics, structure, diversity

and activity of planktonic micro-organisms.

48 Hydrobiologia (2011) 659:37–48

123