Cyanobacteriales (Gibbons and Murray 1978). Stanier et al. (1971) coined the name
cyanobacteria, and classification of cyanobacteria alongside the bacteria was considered as a truer representation of their phylogenic position. In 1977, Stanier and
Cohen-Bazire stated that the only logical taxonomic treatment of cyanobacteria was
to place them in the super kingdom Prokaryotae as a division, class, or order of
bacteria: the Cyanobacteria.
Traditional classifications are based upon morphological features of the organisms. The main morphological features used in classification of cyanobacteria are
growth form (unicellular, colonial, filamentous), shape of the colonies, shape of the
filaments, sheath (present or absent), cell differentiation (presence of heterocysts or
not), size and shape of vegetative cells, branching (present or absent), and combinations of these different characters.
Cyanobacteria include around 5 orders, 150 genera, and around 2000 species.
The five orders of cyanobacteria recognized in the classic botanical taxonomic
scheme are:
1. Chroococcales: These are the coccoid cells that are reproduced by binary fission
or budding. The representative genera are Aphanocapsa, Aphanothece,
Gloeocapsa, Merismopedia, Microcystis, Synechococcus, Synechocystis, etc.
2. Pleurocapsales: These are coccoid cell aggregates, or pseudo-filaments in
nature that are reproduced by baeocytes; Chroococcidiopsis and Pleurocapsa
are the representative genera of this order.
3. Oscillatoriales: They have uniseriate filaments, without heterocysts or akinetes
for example Lyngbya, Leptolyngbya, Microcoleus, Oscillatoria, Phormidium,
Planktothrix, etc.
4. Nostocales: Characteristics of this order are filamentous cyanobacteria that divide
in only one plane, with heterocysts, false branching in genera such as Scytonema,
Anabaena, Aphanizomenon, Calothrix, Cylindrospermopsis, Nostoc, Scytonema,
Tolypothrix, etc.
5. Stigonematales: Stigonematales divide in more than one plane with true
branching and multiseriate forms with specialized cells known as heterocysts.
Mastigocladus and Stigonema are the representative genera of this group.
The classical conventions used in the classification of cyanobacteria frequently
proved unsatisfactory, and a symptom of this undesirable stage of affairs is that
conventional taxonomy frequently appears to have been ignored by physiologists
and biochemists (Whitton 1969). Because, they are morphological simple and occur
in polymorphism which aggravated the problem of identification of the organisms
based on morphological characters and sometimes variations (polymorphism) in
response to changes in environmental conditions. Recent trends on classification of
cyanobacteria are based on its dynamic characters, physiological properties, fatty
acid composition, presence of pigments, isozymes, genome size, deoxyribonucleic
acid base composition, sequence-specific deoxy ribonucleases, DNA-DNA hybridization, etc (Figs. 16.1 and 16.2).
16 Cyanobacteria: The Eco-Friendly Tool for the Treatment of Industrial Wastewaters
391
cyanobacteria, and classification of cyanobacteria alongside the bacteria was considered as a truer representation of their phylogenic position. In 1977, Stanier and
Cohen-Bazire stated that the only logical taxonomic treatment of cyanobacteria was
to place them in the super kingdom Prokaryotae as a division, class, or order of
bacteria: the Cyanobacteria.
Traditional classifications are based upon morphological features of the organisms. The main morphological features used in classification of cyanobacteria are
growth form (unicellular, colonial, filamentous), shape of the colonies, shape of the
filaments, sheath (present or absent), cell differentiation (presence of heterocysts or
not), size and shape of vegetative cells, branching (present or absent), and combinations of these different characters.
Cyanobacteria include around 5 orders, 150 genera, and around 2000 species.
The five orders of cyanobacteria recognized in the classic botanical taxonomic
scheme are:
1. Chroococcales: These are the coccoid cells that are reproduced by binary fission
or budding. The representative genera are Aphanocapsa, Aphanothece,
Gloeocapsa, Merismopedia, Microcystis, Synechococcus, Synechocystis, etc.
2. Pleurocapsales: These are coccoid cell aggregates, or pseudo-filaments in
nature that are reproduced by baeocytes; Chroococcidiopsis and Pleurocapsa
are the representative genera of this order.
3. Oscillatoriales: They have uniseriate filaments, without heterocysts or akinetes
for example Lyngbya, Leptolyngbya, Microcoleus, Oscillatoria, Phormidium,
Planktothrix, etc.
4. Nostocales: Characteristics of this order are filamentous cyanobacteria that divide
in only one plane, with heterocysts, false branching in genera such as Scytonema,
Anabaena, Aphanizomenon, Calothrix, Cylindrospermopsis, Nostoc, Scytonema,
Tolypothrix, etc.
5. Stigonematales: Stigonematales divide in more than one plane with true
branching and multiseriate forms with specialized cells known as heterocysts.
Mastigocladus and Stigonema are the representative genera of this group.
The classical conventions used in the classification of cyanobacteria frequently
proved unsatisfactory, and a symptom of this undesirable stage of affairs is that
conventional taxonomy frequently appears to have been ignored by physiologists
and biochemists (Whitton 1969). Because, they are morphological simple and occur
in polymorphism which aggravated the problem of identification of the organisms
based on morphological characters and sometimes variations (polymorphism) in
response to changes in environmental conditions. Recent trends on classification of
cyanobacteria are based on its dynamic characters, physiological properties, fatty
acid composition, presence of pigments, isozymes, genome size, deoxyribonucleic
acid base composition, sequence-specific deoxy ribonucleases, DNA-DNA hybridization, etc (Figs. 16.1 and 16.2).
16 Cyanobacteria: The Eco-Friendly Tool for the Treatment of Industrial Wastewaters
391