Cyanobacteria produce toxins that attack various organs
such as the liver (hepatotoxins) and nervous system
(neurotoxins) and less dangerous toxins that can affect the
skin or cause gastroenteritis. The toxins are usually released
at the time of death and cell lysis*. Neurotoxins are alkaloids,
and some of them are closely related to the paralytic toxin
(saxitoxin). Hepatotoxins or microcystins are heptapeptides
with more than 50 types that have been described. The best
known is microcystin-LR which can retain its activity for
several weeks after release into the environment (Box 15.2).
There are about forty species of cyanobacteria producing
various toxins. The neurotoxins are produced by the genera
Anabaena, Aphanizomenon, and Oscillatoria. Concerning
hepatotoxins, they are also synthesized by these three genera
plus Microcystis, Nodularia, and Nostoc. The species most
often involved in the formation of algal blooms in freshwater are Anabaena flosaquae, Aphanizomenon flosaquae,
Microcystis aeruginosa, and Planktothrix agardhii (Box 15.2).
Microcystis aeruginosa is a potentially toxic cyanobacteria present in freshwater (lakes, ponds, rivers) where
it can develop important blooms. This organism synthesizes
hepatotoxins, microcystins, which can lead to fish (threat to
aquaculture) and birds’ death. These toxins also pose a risk
to human health because they cause liver disorders and
skin problems. In Brazil in 1996, renal dialysis done with
badly purified water caused 60 deaths due to these toxins.
The prevalence of Microcystis aeruginosa in France is not
well known in the absence of specific environmental studies,
but problems associated with the proliferation of these
cyanobacteria have been reported in many countries
(UK, Finland, Australia, USA, China, etc.).
15.2.4 Fungi
Fungi are classified in their own kingdom (cf. Sects. 5.5.3 and
7.14.3). They are heterotrophic eukaryotic organisms that
acquire their nutrients by absorption. They secrete powerful
enzymes that digest their food externally. They have body
structures and modes of reproduction unlike those of any
other organism. Fungi can be unicellular or multicellular.
A typical fungus consists of thin filaments called hyphae*.
Hyphae can branch repeatedly forming a feeding network
called mycelium*. Most fungi, including the molds and
mushrooms, are multicellular but yeasts are unicellular. The
fungal cells are composed of a core in which we find the
chromosomes. Fungi are divided roughly into two main groups,
the “macro-fungi” (or macrofungi) and “micro-fungi” (or microfungi). A hundred species of microfungi can cause infections
in humans, infections called mycoses. These species are differentiated into primary pathogens, that is to say, can infect healthy
individuals, or opportunistic agents infecting individuals that
can be vulnerable for various reasons including a weakening
of their immune system. These agents are classified according
to their morphology and some molecular markers. The main
genera that have pathogenic species are Aspergillus, Candida,
Epidermophyton, Microsporum, Trichophyton (fungi
ascomycetes), and Cryptococcus (fungi basidiomycetes).
Fungal infections (mycoses) can be divided according
to the severity of symptoms into two broad categories, superficial and systemic infections. Superficial infections affecting
the skin, the hair, and the nails are due to dermatophytes.
Systemic fungal infections occur when fungi get into the
bloodstream and colonize organs including the lungs and
even the central nervous system. These infections are often
associated with immunodeficiency. The incidence of fungal
infections is increasing due to the increase in diabetes, AIDS,
and treatments requiring the use of immunosuppressive
drugs. Aspergillosis, candidiasis, and cryptococcosis are
among the main human mycoses, and microfungi responsible
for these infections belong, respectively, to the genera Aspergillus, Candida, and Cryptococcus.
Aspergillus fumigatus is a filamentous fungus and is the
principal agent of aspergillosis. It produces cleistothecium,
closed ascocarps with asci scattered rather than gathered in a
hymenium. This fungus is found in the environment and
plays a role in the recycling of organic matter. Its spores
are in frequent contact with humans and may migrate into
the respiratory tract to the pulmonary alveoli, where they can
cause severe disease in immunocompromised patients.
The bronchopulmonary aspergillosis can progress to abscess
formation. Invasive aspergillosis is characterized by blood
spread, and the outcome is often fatal.
Box 15.2 (continued)
strain (M. aeruginosa PCC7806) and its nontoxic
mutant, seem to suggest that microcystins may have
pleiotropic actions in the cellular metabolism.
To conclude, freshwater cyanobacteria are the
focus of many studies aiming to better understand
why they proliferate in these ecosystems, what are
the health risks associated with these blooms, and
what is the functional role of cyanotoxins. The interest
for these microorganisms for the scientific community,
but also for managers of aquatic systems as well as for
health authorities, is increasing, in conjunction with
the increase in the number of ecosystems displaying
cyanobacterial blooms in the last 30 years. This
increase was linked to local and global changes and,
in particular, to the pollution of many freshwater
ecosystems by nutrients, especially phosphorus.
In addition, very recent works also suggested that
more global pressures, such as global warming, could
contribute to the development of cyanobacterial blooms
in freshwater ecosystems (Paerl and Huisman 2009).
628
P. Lebaron et al.
such as the liver (hepatotoxins) and nervous system
(neurotoxins) and less dangerous toxins that can affect the
skin or cause gastroenteritis. The toxins are usually released
at the time of death and cell lysis*. Neurotoxins are alkaloids,
and some of them are closely related to the paralytic toxin
(saxitoxin). Hepatotoxins or microcystins are heptapeptides
with more than 50 types that have been described. The best
known is microcystin-LR which can retain its activity for
several weeks after release into the environment (Box 15.2).
There are about forty species of cyanobacteria producing
various toxins. The neurotoxins are produced by the genera
Anabaena, Aphanizomenon, and Oscillatoria. Concerning
hepatotoxins, they are also synthesized by these three genera
plus Microcystis, Nodularia, and Nostoc. The species most
often involved in the formation of algal blooms in freshwater are Anabaena flosaquae, Aphanizomenon flosaquae,
Microcystis aeruginosa, and Planktothrix agardhii (Box 15.2).
Microcystis aeruginosa is a potentially toxic cyanobacteria present in freshwater (lakes, ponds, rivers) where
it can develop important blooms. This organism synthesizes
hepatotoxins, microcystins, which can lead to fish (threat to
aquaculture) and birds’ death. These toxins also pose a risk
to human health because they cause liver disorders and
skin problems. In Brazil in 1996, renal dialysis done with
badly purified water caused 60 deaths due to these toxins.
The prevalence of Microcystis aeruginosa in France is not
well known in the absence of specific environmental studies,
but problems associated with the proliferation of these
cyanobacteria have been reported in many countries
(UK, Finland, Australia, USA, China, etc.).
15.2.4 Fungi
Fungi are classified in their own kingdom (cf. Sects. 5.5.3 and
7.14.3). They are heterotrophic eukaryotic organisms that
acquire their nutrients by absorption. They secrete powerful
enzymes that digest their food externally. They have body
structures and modes of reproduction unlike those of any
other organism. Fungi can be unicellular or multicellular.
A typical fungus consists of thin filaments called hyphae*.
Hyphae can branch repeatedly forming a feeding network
called mycelium*. Most fungi, including the molds and
mushrooms, are multicellular but yeasts are unicellular. The
fungal cells are composed of a core in which we find the
chromosomes. Fungi are divided roughly into two main groups,
the “macro-fungi” (or macrofungi) and “micro-fungi” (or microfungi). A hundred species of microfungi can cause infections
in humans, infections called mycoses. These species are differentiated into primary pathogens, that is to say, can infect healthy
individuals, or opportunistic agents infecting individuals that
can be vulnerable for various reasons including a weakening
of their immune system. These agents are classified according
to their morphology and some molecular markers. The main
genera that have pathogenic species are Aspergillus, Candida,
Epidermophyton, Microsporum, Trichophyton (fungi
ascomycetes), and Cryptococcus (fungi basidiomycetes).
Fungal infections (mycoses) can be divided according
to the severity of symptoms into two broad categories, superficial and systemic infections. Superficial infections affecting
the skin, the hair, and the nails are due to dermatophytes.
Systemic fungal infections occur when fungi get into the
bloodstream and colonize organs including the lungs and
even the central nervous system. These infections are often
associated with immunodeficiency. The incidence of fungal
infections is increasing due to the increase in diabetes, AIDS,
and treatments requiring the use of immunosuppressive
drugs. Aspergillosis, candidiasis, and cryptococcosis are
among the main human mycoses, and microfungi responsible
for these infections belong, respectively, to the genera Aspergillus, Candida, and Cryptococcus.
Aspergillus fumigatus is a filamentous fungus and is the
principal agent of aspergillosis. It produces cleistothecium,
closed ascocarps with asci scattered rather than gathered in a
hymenium. This fungus is found in the environment and
plays a role in the recycling of organic matter. Its spores
are in frequent contact with humans and may migrate into
the respiratory tract to the pulmonary alveoli, where they can
cause severe disease in immunocompromised patients.
The bronchopulmonary aspergillosis can progress to abscess
formation. Invasive aspergillosis is characterized by blood
spread, and the outcome is often fatal.
Box 15.2 (continued)
strain (M. aeruginosa PCC7806) and its nontoxic
mutant, seem to suggest that microcystins may have
pleiotropic actions in the cellular metabolism.
To conclude, freshwater cyanobacteria are the
focus of many studies aiming to better understand
why they proliferate in these ecosystems, what are
the health risks associated with these blooms, and
what is the functional role of cyanotoxins. The interest
for these microorganisms for the scientific community,
but also for managers of aquatic systems as well as for
health authorities, is increasing, in conjunction with
the increase in the number of ecosystems displaying
cyanobacterial blooms in the last 30 years. This
increase was linked to local and global changes and,
in particular, to the pollution of many freshwater
ecosystems by nutrients, especially phosphorus.
In addition, very recent works also suggested that
more global pressures, such as global warming, could
contribute to the development of cyanobacterial blooms
in freshwater ecosystems (Paerl and Huisman 2009).
628
P. Lebaron et al.