Cryptogamie, Algal., 1999, 20 (3): 209-222
209
Generic characters of the simplest cyanoprokaryotes
Cyanobium, Cyanobacterium and Synechococcus
Jift’ KOMAREK”,
JiH KOPECK$
& Vladislav
CEPAK
a University of South Bohemia, Faculty of Biological
Sciences, Braniiovsti
31,
37005 Ceske’ BudfTjovice, Czech Republic; [email protected]
b Czech Academy of Sciences, Institute of Microbiology,
Opatovicky’ mlyn,
37981 TYeboii, Czech Republic
’ Masaryk University, Faculty of Science, Dept. of Plant Physiology and Anatomy,
KotWska
2, 61137 Bmo, Czech Republic
(Received
I June 1997, accepted
20 June 1999)
Abstract - The cytomorphological features (cell morphology, type of cell division, cell structure,
structure of photosynthetic apparatus) were studied in the type strains of the cyanoprokaryotic
genera Cyanobium and Cyanobacterium, and in the reference strain of the traditional genus
Synechococcus (Synechococcus PCC 6301; = “‘Anacystis nidulans” sensu auct.). They were
originally described by Rippka & Cohen-Bazire, based on the mean DNA-base composition
(moles % G + C) and on the resistance to various cyanophages. The phenotypic diacritical
characters were found to coincide well with the molecular markers, and thus, the genera Cyanobium
and Cyanobacterium are acceptable also according to the traditional (botanical) taxonomic criteria.
The integrated molecular, cytomorphological
and ecophysiological approaches to the solution of
taxonomic problems in cyanobacteria are therefore inevitable for taxonomic evaluation, from the
methodological point of view. The lists of species within the revised genera Cyanobium and
Cyanobacterium are reviewed. 0 ADAC / Elsevier, Paris
classification I Cyanobacteria I Cyanobacterium I Cyanobium
pigments / Synechococcus 1 taxonomy / unicellular genera
I cyanoprokaryotes
I cytology I
R&urn6 - Les caracteristiques cytomorphologiques
(morphologie de la cellule, type de division
cellulaire, structure cellulaire, structure de l’appareil photosynthetique) ont Cte &dies chez la
souche type des genres cyanoprocaryotiques Cyanobium et Cyanobacterium, ainsi que chez la
souche de reference du genre traditionnel Synechococcus (Synechococcus PCC 6301 ; = N Anacystis nidulans >> sensu auct.). Ces genres ont Cte d&its originellement par Rippka & CohenBazire, sur la base de la composition moyenne en bases du DNA (% moles G + C) et sur la
resistance a des cyanophages varies. 11 a Cte montre que les caracteres phenotypiques distinctifs
comcidaient bien avec les marqueurs moleculaires, en consequence, les genres Cyanobium et
Cyanobacterium sont acceptables aussi selon les criteres taxinomiques traditionnels (botaniques).
L’integration
des approches moleculaires, cytomorphologiques
and Ccophysiologiques est done
inevitable pour la solution des problemes taxinomiques chez les cyanobacteries. Les listes des
espbces des genres revises Cyunobium et Cyanobacterium ont ete examinees. (Traduit par la
Redaction.) 0 ADAC / Elsevier, Paris
classification I Cyanobacteria I Cyanobacterium I Cyanobium
genres unicellulaires
/ pigments / Synechococcus I taxinomie
I cyanoprocaryotes
I cytologic 1
This paper is dedicated to the memory of Prof. Dr Pierre Bourrelly and Prof. Dr Roger Y. Stanier.
210
J. Kom&rek, J. KopeckJi & V. Cep&
INTRODUCTION
The traditional cyanoprokaryotic
(Cyanophycean, Cyanobacterial) genus Synechococcus Nageli 1849 lacks mucilage, lives as solitary cells (several species as
picoplanktic organisms), or in aggregated clusters, but never forms delimited, gelatinous
colonies. The cells are slightly or distinctly elongated (oval to rod-like) and divide only
cross-wise, in one and the same plane in successive generations. From this genus, the
genus Cyunofhece was separated on the basis of serious cytomorphological (KomSrek,
1976) and ultrastructural
(Komarek & Cepiik, 1998) features. In 1983, Rippka &
Cohen-Bazire defined two other genera, which correspond morphologically with the
original Synechococcus-type, namely Cyanobium and Cyanobacterium, on the basis of
different mean DNA-base composition and sensitivity to various cyanophages.
In our study, we describe the phenotypic and structural features of the type
strains of two Rippka & Cohen-Bazire’s genera (which were not yet studied) and their
Synechococcus-strain
PCC 6301, which is not the type species of this genus (it is
S. elongatus), but was used by Rippka & Cohen-Bazire as an available example of the
characteristic Synechococcus species for comparison. Important differences in cell
structure and in morphological variation were found between them, corresponding well to
the intergeneric characters commonly used in the traditional taxonomy of simple
cyanoprokaryotes.
METHODS
Cultivation
The following strains were used from the Pasteur Culture Collection (PCC):
Synechococcus PCC 6301, Cyunobium PCC 6307 (= UTEX 1548), and Cyanobacterium
PCC 7202 (= CCAP 1479/2a). The strains were cultured in suspension in Erlenmayer
flasks in the medium ‘28 >>after Zehnder (Staub, 1961), under a normal day light regime
in January 1997, at a temperature of 20-23 “C. The both strains of Cyunobium and
Cyanobacterium are designated as the generic type strains in Rippka & Cohen-Bazire
(1983) (according to the bacteriological Code), the strain of Synechococcus as “the typical
reference-strain”. The designation of the strain Synechococcus PCC 6301 as “typical” is
problematic from a nomenclatural point of view, since it does not belong to the type
species Synechococcus elongatus (Nageli) Nageli 1849, which must provide the type of
the genus name Synechococcus (ICBN Art. 10.1) despite the fact that no original strain
of S. elongatus has been preserved. However, the main aim of this study is the comparison
of the intergeneric features based on strains just selected by Rippka & Cohen-Bazire
(1983). Morphology was studied under the light microscope Leitz-Dialux 22. The cell
division was studied on the agar plates (with 2 % agar) under the same culture conditions.
Ultrastructure
The samples were fixed with 2.5 % glutaraldehyde, washed with 0.1 M
cacodylate buffer and transferred into agar. Postfixation was done with 2 % 0~0, in the
same buffer and washed again with cacodylate buffer with glucose after 4 h. The acetone
Generic characters of the simplest cyanoprokaryotes
211
row was used for dehydration. The sections were contrasted by a concentrated
uranylacetate solution in 50 % ethanol, followed by an aqueoussolution of Pb-citrate.
Pigments
The chromatographic system consistsof a Beckman Model 420 gradient liquid
chromatograph (Beckman Instruments) equipped with a Waters 991 photodiode array
detector (Millipore). All solventswere HPLC grade and obtained from Sigma. Spherisorb
ODS-1 non-endcapped liquid chromatographic column (5 pm particle size,
250 mm x 4.6 mm LD) was from Altech. The mobile phase gradient was employed
according to Gilmore & Yamamoto (1991) and consistsof two isocratic and two linear
gradient parts asfollows: the mobile phaseA was run isocratically within the first 4 min,
followed by a 2.5 min linear gradient to the 100 % mobile phaseB. After the next 6 min,
an isocratic step was followed for 2 min by a linear gradient back to the 100 % mobile
phase A. Solvent mixtures were: (A) Acetonitrile:Methanol:Tris buffer 0.1 M pH 8
(79:8.7:3.3); (B) Methanol:Hexane (4:l). The column was re-equilibrated between
individual sampleswith mobile phaseA, for a minimum of 6 min. The flow rate for all
separationswas 2 mlmin-‘. The volume of the sampleinjection loop was 20 fl.
Pigments were extracted at room temperature, under dim laboratory light. The
cyanobacterial cell-biomass obtained by centrifugation at 6000 RPM for 15 min was
resuspendedin 0.25 ml 100 % cold acetone. The appropriate amount of glassbeadswas
addedto this sediment together with several mg of MgCO,, and disintegrated for 3 min
at room temperature with intenseVortex mixing. The homogenisatewas allowed to stay
for 5 min, centrifuged, and the resulting supernatantsaved into calibrated test tube. The
pellets of cells were re-extracted to ensure complete extraction. The supematant was
pooled and then filtered through 0.2 pm Sartorius filters. The extracts were analysed
immediately by HPLC. No pigment degradation was observed.
Nucleoids
Nucleoids were contrasted by DAPI-staining according to Zachleder & Cep&
(1987). A drop of suspensionwas put on a slide and drop of DAPI solution in
concentration of lpgmin-’ in buffer S was added. The preparationswere examined with
an epifluorescencemicroscope JENALUMAR (Carl Zeiss Jena). The fluorescenceof the
DAPI-DNA-complex was excited by light from an HBO-202W mercury vapour lamp and
using an UG-1 (UV-transmitting) excitation filter and a 450 nm suppressionfilter.
RESULTS
Morphology
All three strainsbelong to the simplest cyanoprokaryotic organisms,living as
solitary, oval to cylindrical cells. They form homogeneoussuspensionin culture and
intensemucilage production was not registered.Cell division is always by binary fission,
which proceedsperpendicularly to the longer cell axis, and occurs in the sameplane in
successivegenerations. In Cyanobacterium stanieri and SynechococcusPCC 6301 the
J. Komtiek, J. Kopecky & V. Cepak
212
asymmetrical cell division of elongatedcells occurs under the suboptimalconditions. This
elongation of cells accompaniedby unequal division was not observedin the Cyanobium
PCC 6307. The main cell forms and size limits of all three strains are included in
Figs l-3 and Tab. 1.
Figs l-3. Morphology of cells of studied strains. Fig. 1. Cyanobacterium stanieri, strainPCC7202.
Fig. 2. Cyanobium gracile, strainPCC6307. Fig. 3. Synechococcus strainPCC 6301.-Orig.
Tab. 1. Characteristics
of thetype (or reference)strainsfrom thePasteurCultureCollection(PCC).
GC
(moles %)
F’CC 6301
Syneckococcus
56
Positive
hosting to
cyanopkages
AS-1M
AS-1
Cell
dimensions
1.2-3 x
H.61
pm
Cell division
SpUl~l hiCd
Tkylokoid
pattm
Involution
cells
Nucleoids
(mqkol.)
96 PE
Cell
form
peripheral
filamentous
band-like
14.4
rod-like
peripheral
ilTeglllLXI
band-like
6.4
oval
irregular
lengthwise
shortly
filamentous
ilEglllEU
granular
net-like
17.8
widely
oval to
rod-like
curved
(asymmetrical)
SP.
PCC 6307
(UTEX 1548)
Cyanobium
gracile
PCC 7202
(CCAP 147912a
Cyanobacterium
stanieri
66-71
39
0.4-2.4 x
fo.25XI.4
pn
SM-I
SM-2
SplIWiCd
3.7-X2(15)
x symmehical
1.7-3.4 pm
(asymmetical)
to
Generic characters ‘of the simplest cyanoprokaryotes
213
Cell structure
Distinct qualitative differences were found between the Synechococcus PCC
6301 + Cyanobium PCC 6307 strains, and Cyanobacterium PCC 7202. While thylakoids
are situated distinctly peripherally in the SynechococcusKyanobium
cluster (Figs 4-9),
they are situated irregularly and densely lengthwise in Cyanobacterium (Figs 10-14). In
thylakoid arrangement only the quantitative differences were recorded under different
cultivation conditions, depending on the age of culture, or on the age of cells in one and
the same strain. The basic thylakoid arrangement always remained identical in various
strains studied and correspond to similar types of simple cyanoprokaryotes
(see, e.g.
Gantt & Conti, 1969; Komarek & Ccpak, 1998).
In
nucleoid
structures,
(Figs 15-18)
the
close
similarity
in
SynechococcusKyanobium
cluster also exists, where nucleoids are in the form of
elongated bands. In Cyanobacterium, they form massive, irregular-granular to net-like
patterns in the cell center, which are well comparable with other morphologically
analogous strains KOVACIK
1986/4 (CCALA) (Fig. 18) and SAG 88.79 (Cepak et al.,
1991, fig. 1 lot. cit.) of Cyanothece cedrorum.
Pigments
The phycobilin composition (red cells, PC:PE ratio) was used several times for
characterization of various cyanobacterial taxonomic units (e.g. in Waterbury & Rippka,
1989; Waterbury et al., 1986; and others). No distinct differences in PC and PE contents
exist in type strains of three genera studied (Tab. 2). Phycoerythrin is always present, the
lowest values were found in Cyanobium gracile (Tab. 1). However, the red species in
Cyanobium-cluster
are also known, and the PUPE ratio can be considered at least as
strain- and species-specific only.
A somewhat different situation occurs in carotenoid composition (Fig. 19). In all
strains distinct peaks were found indicating zeaxanthin and a-carotene (Fig. 19,3 and 5);
the lowest peak of the first one (3) in Cyanobacterium stanieri has a rather quantitative
character. However, further carotenoids (1, 2) were examined, from which no. 2 appeared
in quantity in Synechococcus PCC 6301, but in traces in both other strains. The
unidentified carotenoid (2) had distinct peaks in Cyanobium and Synechococcus, but it is
completely lacking in Cyanobacterium (Fig. 19, arrow). This qualitative absence represents a greater divergence of Cyanobacterium PCC 7202 from two other strains.
DISCUSSION
AND TAXONOMIC
CONCLUSIONS
Our results indicate agreement between cytomorphological
and molecular
features of the simplest unicellular cyanobacteria (see also Komarek, 1996). The genera
Cyanobium, Cyanobacterium and Synechococcus are distinguishable on a molecular basis
and are acceptable also based on the phenotypic characters. Even though our results can
not be generalized, they illustrate the coincidence of molecular and phenotype characters
of different cyanobacterial types. The combination of molecular, cytomorphological and
ecophysiological approaches to solve problems in cyanobacterial taxonomy is therefore
necessary.
The cytomorphological characters can be used to a certain degree in keys for the
identification of cyanobacteria of this type. In three species, which correspond morpho-
J. Komtiek,
214
J. Kopecky & V. Cep&
6
8
Figs 4-9. Fine sections of cells in species with parietal thylakoids. Figs 4-7. Cyanobium gracile
(Figs 5-6 = cell division, Fig. 7 = cross-section). Figs 8-9. Synechococcus strain PCC 6301
(Fig. 8 = cross-section). k = carboxysomes, p = polyphosphates, t = thylakoids, w = cell wall.
Generic characters of the simplest cyanoprokaryotes
215
Figs l&14. Fine sections of cells of fZyunobucterium stanieri. Fig. 10. Cell after division lengthwisesection. Figs 11-13. Tangential sections. Fig. 14. Detail of cell protoplast from
Fig. 11with lengthwise oriented thylakoids and easily remarkable phycobilisomes.
k = carboxysomes,
p = polyphosphates,
t;= thylakoids,w = cell wall.
logically to the genus Cyanobium (C. gracile, Synechococcus virga-rosea Chang, and
Synechococcus sp. div. sensuWaterbury et al., 1986), the limits were found between
59-70 % mol G/C (Rippka & Cohen-Bazire, 1983; Chang, 1980; Waterbury et al, 1986).
The single known exception is C. rubescens,in which only 36 % mol. G/C was found
according to Chang (1980), but all other characters correspond completely with other
Cyanobium species, particularly with C. virga-rosea. The combination of various
evaluation methods is therefore inevitable for cyanobacterial taxonomic revisions.
216
J. Komtiek,
t
1516 10 pm
I
J. Kopeck? & V. Cep&
I
4
17-18 10 pm
Figs 15-18. Nucleoid structure in studied strains. All species are documented by identical phcLaos,
from which u represents the view from optical microscope, b after DAPI staining with characteristic
nucleoid structure. Fig. 15. Cyanobium gracile strain PCC 6307. Fig. 16. Synechococcus strain PCC
6301. Fig. 17. Cyanobacterium stanieri strain PCC 7202. Fig. 18. Cyanobacterium cedrorum strain
KOVACIK
1986/4 (CCALA).
Generic characteqs of the simplest cyanoprokaryotes
217
Tab. 2. Contents of phycocyanin (PC), allophycocyanin (APC) and phycoerythrin
studied strains. The percentage counted according to Bennett & Bogorad (1973).
PC
mg.rn-’
Cyanobacterium
APC
II
(PE) in three
PE
2 PBP
%
IngIn-
%
mgm-’
%
0.0068
60.8
0.0024
21.4
0.0020
17.8
0.0112
0.0271
82.6
0.0036
11.0
0.0021
6.4
0.0328
0.0193
64.8
0.0062
20.8
0.0043
14.4
0.0298
PCC 7202
Cyanobium
PCC 6307
Synechococcus
PCC 6301
Cyanobacterium
PCC 7202
0.18 -
Synechococcus
PCC 6301
Cyanobium
PCC 6307
4
4
4
0.16
0.14 1
i! 0.12 3
G 0.10 8
z 0.08 2
E: 0.06 3
0.04 -
3
J-+AJJ
L-.&AL
1
0.00
0
2
4
6
810
120
2
i
I
I
I
I
I
2
4
6
8
10
TIME
5
.J!
3
5
I
120
2
1
I
I
I
I
I
2
4
6
8
10
12
[min]
Fig. 19. Pigment composition in studied strains: 1-2 = unidentified
4 = chlorophyll a, 5 = a-carotene.
carotenoids, 3 = zeaxanthine,
and both the genera Cyanobium and
by Rippka & Cohen-Bazire (1983), are
also definableby the combined cyto orphological and nucleoid structural characters.The
strict0
218
J. Komtiek, J. Kopecky & V. Cep&
results suggest closer relationships between Synechococcus
and Cyanobium (with the
identical thylakoid arrangement), while the genus Cyanobacterium
is evidently more
distant from them in respect to cell structure (particularly in thylakoid arrangements)and
severalother criteria (carotenoids, nucleoid structure). The diagnostic featuresof all these
three genera are included in Tab. 3, but they must be confirmed by sequencingmethods.
Tab.3. Characteristics
of the generaSynechococcus, Cyanobiun
Genus
GC
(moles %)*
(36)
Cell form
Cell dimensions
W)
Type of
perpendicular
binary jission
symmetric,
pinching
parietal
irregular
band-like
symmetric or
asymmetric,
cleavage
parietal
filamentous
band-like
lengthwise
irregular to irregular
shortly
granular
filamentous net-like
54.5-71
oval to short
rod-like with
rounded ends
(0.4)14(4.5)
0.2-3(6 ?)
Synechococcus
41-56
cylindrical
1.2-28(68)
(0.4)16(7)
Cyanobacterium
39-41
cylindrical to
widely oval
(2)3.4-12(30)
2-7(20)
Cyanobium
and Cyanobacterium.
x
x
x symmetric or
asymmetric,
cleavage
Thylakoid
pattern
Involution
cells
Nucleoids*
to
* Derivedfrom the type speciesandseveralknown strains published by Chang (1980), Waterbury
et al. (1986)andWaterbury& Rippka(1989).
A problem concerning the typification arisesfor taxonomic treatment. Because
the type speciesof the genera Cyanobium (C. gracile) and Cyanobacterium
(C. stanieri)
were validly publishedunder the bacteriological Code, thesenamesare treated asvalidly
published at the sametime under the botanical Code (ICBN, Art. 45.5). The type strains
of the genera Cyanobium and Cyanobacterium
can therefore be used for typification in
our study, but the samemethod was impossiblein the caseof Synechococcus. This genus
was describedby Nageli in 1849, and the type strain doesnot exist. Moreover, we did not
find any characteristic strain of the type speciesS. elongatus in world collections. Rippka
& Cohen-Bazire (1983) usedtherefore for comparisonthe “reference strain PCC 6301”,
formerly known as “Anacystis nidulans”.
It is difficult to define the generic ultrastructural
characters of the whole genus Synechococcus
on the basis of our results, but the
intergeneric differences between that type and both genera Cyanobium and particularly
Cyanobacterium
are well recognized.
It is probable that further investigations will yield some data intermediate
between the defined genera, particularly in molecular characters (G/C ratio), pigment
contents, and ecophysiological characters. However, several known features seemto be
stable to such a degree that differentiation on the generic level is acceptable (thylakoid
position, type of cell division).
The application of newly defined generic criteria (Tab. 3) justifies the taxonomic
revision of all species originally described under the generic name Synechococcus.
Therefore, we summarize all the Cyanobium and Cyanobacterium
species,describedup
to now, in which the corresponding ultrastructural and/or morphological (phenotype)
characterswere recognized, into the following list (someof them recombinedfrom other
genera).
Generic character$ of the simplest cyanoprokaryotes
219
The1 genus Cyanobium
All species corresponding o the diagnostic features of the genus Cyanobium
defined above should be included in is genus. Several of them have not been studied yet
in culture and their cytology and bi chemical characters must be determined. Transfer
into the genus Cyanobium for seve al species is acceptable because their phenotypic
appearance corresponds fully with
e generic diagnosis. The corresponding nomenclatural transfers should provide a basi for further investigations for the following species
and are necessary for the monogra hit review of coccal cyanoprokaryotes
(figs and
descriptions in Komarek & Anagno 1 tidis, 1998). Description is added only for the type
species, C. gracile.
- Cyanobium gracile Rippka and Cohen-Bazire, 1983, Ann. Microbial. (Inst. Pasteur)
134B: 32; type species (Figs lb, 2A)j Cells solitary, cyanoprokaryotic, without mucilage,
shortly oval, pale blue-green, with homogeneous content, 0.4-2.4 x 0.2-0.4 pm, dividing
transversely, with parietal thylakoids GC-content = 70 % mol. (Description according to
the type strain PCC 6307; camp. Ri pka & Cohen-Bazire, Zoc. cit., p. 32.)
b
- Cyanobium amethystinum
(Co land) comb. nov.; [basionym: Synechococcus
amethystinus Copeland, 1936, Ann. .I: Acad. Sci. 36: 51; syn.: Cyanothece amethystina
(Copeland) Kom&-ek, 1976, Arch. PT otistenk. 118: 1481.
- Cyanobium bacillare (Butcher)
omb. nov.; [basionym: Synechococcus bacillaris
Butcher, 1952, J. Max Biol. Assoc. .K. 3 1: 1891.
- Cyanobium diatomicola (Geitler) omb. nov.; [basionym: Synechococcus diatomicola
Geitler, 1953, dsterr. bot. Ztschr. 110, 3: 3011.
- Cyanobium eximium (Copeland) comb. nov.; [basionym: Synechococcus eximius
Copeland, 1936, Ann. N.I: Acad. ci. 36: 50; syn.: Cyanothece eximia (Copeland)
Komarek, 1976, Arch. Protistenk. 118: 1481.
- Cyanobium gaarderi (Alvik) corn . nov.; [basionym: Synechococcus gaarderi Alvik,
1934, Bergens Mus. &b. 1934, nat. r,I 6: 40; syn.: Cyanothece gaarderi (Alvik) Komarek,
1976, Arch. Protistenk. 118: 1481.
- Cyanobium oceanicum (Hall et Cl us) comb. nov.; [basionym: Synechococcus oceanicus Hall et Claus, 1965, Revista Bio . 5 (l-2): 651.
- Cyanobium parvum (Migula) co b. nov.; [basionym: Synechococcus parvus Migula,
1906, Crypt. Germ., Austr., Helvet., xs. 26-27 (Alg.): 123; syn.: Synechococcus minutus
i
W. West, 1912, Roy. Irish Acad. 31:,40
(cited from Komarek, 1976)].
- Cyanobium plancticum (Drews et I.) comb. nov.; [basionym: Synechococcus plancticus Drews et al., 1961, Arch. Mikro iol. 39: 1131.
- Cyanobium roseum (Copeland) c mb. nov.; [basionym: Synechococcus roseus Copeland, 1936, Ann. N.Z Acad. Sci. 36” 51; syn.: Cyanothece rosea (Copeland) Komarek,
1976, Arch. Protistenk. 118: 1481.
- Cyanobium rubescens (Chang)
omb. nov.; [basionym: Synechococcus rubescens
Chang, 1980, Schweiz. Ztschr. Hyd Ti 1. 42(2): 221.
- Cyanobium virga-rosea (Chang)
Chang, 1980, Schweiz. Ztschr.
Numerous other
by various authors evidently
belong to the genus
of cyanobacteria
recently (e.g., by
220
J. Komtiek, J. Kopecky & V. Cep&k
The genus Cyanobacterium
The tbylakoid arrangement in Cyanobacterium stanieri is distinct to such a
degree that the taxonomic separation of this genus can not be questioned. The genus
Cyanobacterium is characterized by oval to cylindrical cells, which divide by binary
fission in two equal parts, or rarely (under stressingconditions) asymmetrically. Their cell
content is not differentiated in centro- and chromatoplasmic regions, but it is finely,
irregularly and indistinctly striated. This striation results from the lengthwise position of
thylakoids, which was proved in the type strain (PCC 7202); however, similar features
were describedalso in various other species(e.g., in Cyanothece cedrorum, strainsSAG
88.79 [Kom&rek & Cep& 19981and Kovahk 198614[Cepak et al., 19911).The strain
RF/l from paddy fields in Taiwan, describedby Chou & Huang (1991) asSynechococcus
sp. evidently belongs in this genus as a special species.The following known species
belong to this genus (figs and descriptions seein Komarek & Anagnostidis, 1998):
- Cyanobacterium stanieri Rippka and Cohen-Bazire, 1983, Ann. Microbial. (Inst.
Pasteur) 134B: 32-33; type species(Fig. la, 3): Cells solitary or two together, rarely
aggregatedwithin very fine, formless mucilage, cylindrical or subcylindrical, blue-green,
more or lesswith homogeneouscontent, 3.7-5.2 (15) x 1.7-3.4 pm, dividing transversely,
symmetrically or asymmetrically, with densely and more or less parallelly arranged
thylakoids over the whole cell protoplast; GC = content 39 % mol. (Description according
to the type strain PCC 7202; camp. Rippka & CohenBazire, Zoc. cit., pp. 32-33.)
- Cyanobacterium cedrorum (Sauvageau) comb. nov.; [basionym: Synechococcus
cedrorum Sauvageau, 1892, Bull. Sot. Bot. France 14, ses. extraord. (CXV); syn.:
Cyanothece cedrorum (Sauvageau) Komarek, 1976, Arch. Protistenk. 118: 1491; this
specieswas transferred to the genusCyanobacterium in respectto the strainsKOVACIK
1986/4 and SAG 88.79 (Cepak et aE., 1991; Komarek & Cepak, 1998). However, the
identity of these strains with the original concept of C. cedrorum is not provable and
should be revised, if possible.
- Cyanobacterium crassiusculum (Skuja) comb. nov.; [basionym: Synechococcus
diachloros var. crassiusculusSkuja, 1956, Nova Acta Reg. Sot. Sci. upsal. 4, 16 (3): 48;
syn.: Cyanothece crassiuscula(Skuja) Komarek et Anagnostidis, 1995, Preslia 67: 191.
- Cyanobacterium diachloros (Skuja) comb. nov.; [basionym: Synechococcusdiachloros
Skuja, 1939, Acta Horti bot. Univ. latv. 11112:43, 1939; syn.: Cyanothece diachloros
(Skuja) Komarek, 1976, Arch. Protistenk. 118: 1491.
- Cyanobacterium minervae (Copeland) comb. nov.; [basionym: Synechococcusminervae Copeland, 1936, Ann. N.I: Acad. Sci. 36: 52; syn.: Cyanothece minervae (Copeland)
Komarek, 1976, Arch. Protistenk. 118: 1481.
- Cyanobacterium notatum (Skuja) comb. nav.; [basionym: Synechococcus notatus
Skuja, 1964, Nova Acta Reg. Sot. Sci. upsal., ser. 4, 18 (3): 23-24; syn.: Cyanothece
notata (Skuja) Komarek, 1976, Arch. Protistenk. 118: 1491.
The genus Cyanothece
The genus Cyanothece was separatedfrom Synechococcusmore than twenty
years ago (Komarek, 1976), but still recently proved its substantial specificity on the
generic level (mainly with respect to the cell-wall structure, thylakoid arrangement,and
nucleoid structure; Komarek & Cepak, 1998). However, only a few speciesfrom this
cluster, which were transferred into Cyanothece originally by Komarek (1976) belong to
this genus.Now, the genusCyanothececomprisesonly six well-defined specieswith more
Generic characters of the simplest cyanoprokaryotes
221
or lessnet-like keritomized protoplasts (Komtiek & Cep& 1998; Komtiek & Anagnostidis, 1998), while the other types with “lengthwise keritomized” (striated) protoplasts
evidently belong to the genus Cyanobacterium.
Acknowledgements.
We are particularly grateful to Dr Rosemarie Rippka (Paris) for the
providing the type strains from Pasteur Institute. We thank also Ing. Jana Nebes$ova PhD (Ceske
Budejovice) for the help in the study of the ultrastructural features of our strains, and Mrs Dana
Svehlova (l?ebofi) for the technical assistance. The study was realized at the Czech Academy of
Sciences, Institute of Botany, Dukelska 145, (32-37982 Eebon< Czech Republic, with the support
of the grant GACR no. 310/95/1191 (headed by Prof. Dr Jan Smarda DSc.).
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