These types of occurrences can cause enormous economic
impact, and the ecological balance is affected by the
blooming of the dinoflagellates.
Unlike the toxic Alexandrium, resting Gymnodinium
catenatum has relatively resistant cell walls, making it
possible to examine fossil records in sediments. The analysis of
210
Pb-dated samples taken from Australian coastal
areas showed that the introduction of G. catenatum into
southern Tasmanian waters occurred around 1972
(Hallegraeff, 1998). Populations of G. catenatum have
been found in Australian ports since the 1990s. The
appearance of G. catenatum coincides with the start of
bulk woodchip exports from southern Tasmania to Japan.
The chemical structures of paralytic shellfish toxins
produced by geographically different populations of
G. catenatum are distinguishable from each other
(Oshima et al., 1993). Their structures are not affected
by temperature, salinity, or nitrate and phosphate concentrations in the culture medium. The major toxins, which
have the N-sulfocarbamoyl group as a substituent and
were produced by the species isolated in 1986 and
1988 from Tasmania, Japan, and the Galicia region of
Spain, were C1 to C4 toxins as well as gonyautoxins
5 and 6. Only the Australian population produced the
novel 13-deoxydecarbamoyl toxins.
Accumulated mutations in rDNA are known to
reflect the prolonged geographic isolation and independent evolution within the region. Genetic analyses of
the toxic dinoflagellates Alexandrium tamarense and
A. catenella were made based on rDNA sequences and
were applied to the interpretation of the biological invasion pathway. The small and large subunit rDNA
sequences show the genetic diversity of A. tamarense
and A. catenella living in Japanese coastal areas
(Scholin et al., 1995). One possible thought is that the
Eastern Asian species was contaminated with the Western European species prior to the 1970s, and diverse
populations taken at ports of call in the Asian region were
introduced into Australian waters via unloaded ballast
water around the 1970s.
Survivability of pathogenic Vibrio cholerae
in environments
Cholera is an epidemiologic syndrome caused by
V. cholerae. The pathogenesis is classified into two groups
based on the serogroups of O1 and O139 (Kaper et al.,
1995). Furthermore, V. cholerae O1 is classified into two
biotypes, classical and El Tor. The seventh pandemic of
cholera, caused by V. cholerae O1 of the El Tor biotype,
has been experienced since 1961 in locations around the
world.
V. cholerae can exist in metabolically inactive states
during which the cultivability of dormant cells declines
but remains alive. The cells in such a “viable but
nonculturable” state are thought to enhance survivability
under harsh conditions. As for the process of becoming
active following dormancy, a recent study on the germination of Bacillus subtilis spores suggests that cell wall
muropeptides released from growing cells serve as the signal molecules for the initiation of growth (Dworkin and
Shah, 2010).
V. cholerae of O1 and O139 serogroups were detected
in more than 93 % of ships (n ¼ 15 ships) calling at ports
in Chesapeake Bay, USA (Ruiz et al., 2000). The numbers of V. cholerae cells having the O1 and O139 antigens in seawater samples were orders of 10
5 and 10
4
colony-forming units (CFU) liter
À1 , respectively.
Although their percentages were approximately 1 %
compared with the total number of cells detected in the
seawater (n ¼ 7 ships), both serotypes had adhered onto
plankton samples. The results indicate that pathogenic
V. cholerae have continuously dispersed into coastal
areas with discharged ballast water, increasing the risk
of human infection with cholera.
Estimation of survivability of V. cholerae in Tokyo
Bay following discharge with ballast water
More than 5,900 overseas vessels have arrived in Tokyo
Bay in recent years. It is natural to assume that large
amounts of ballast water containing pathogenic
V. cholerae have been discharged in the area. Mimura
and Miwa (2013) counted the total population of
colony-forming marine vibrios in samples taken in
Tokyo Bay. The numbers of non-sucrose-metabolized
and sucrose-metabolized vibrio populations on
thiosulfate-citrate-bile salt-sucrose agar plates were less
than 10
4.0 and 10
2.0 CFU ml
À1
, respectively, for all of
the samples (n ¼ 6) (Figure 1). No population that could
make colonies at 37
C was obtained on the plates, and
the population of sucrose-metabolized marine vibrios
was less than 0.16 % of the total bacterial populations
for all of the samples taken in Tokyo Bay.
The estimation of survivability of V. cholerae after dispersal into the coastal area in Tokyo Bay was carried out
using Vibrio sp. as a substitute strain of the pathogenic
V. cholerae (Mimura and Miwa, 2013). The isolate used
in the experiment has physiological and biochemical similarities with those of the pathogen, i.e., they can grow in
37
C and metabolize sucrose as a carbon source
(Mimura et al., 2005). Seawater samples were taken from
Tokyo Bay from June 2009 to March 2010. When the cells
on orders of 10
3 and 10
4 CFU ml
À1 were added to raw seawater samples that had different numbers of native
populations of 10
3.5
–10
6.1 CFU ml
À1 (n ¼ 6 seawater
samples), it was confirmed that no Vibrio sp. cells
survived 2 weeks of incubation at given temperatures,
except in one instance. In the sample in which Vibrio
sp. cells survived, the number of surviving 10
1.6 CFU
ml
À1 out of the initially added 10
3.7 CFU ml
À1 was
obtained under competition with the native population of
MICROBIAL SURVIVABILITY
435
impact, and the ecological balance is affected by the
blooming of the dinoflagellates.
Unlike the toxic Alexandrium, resting Gymnodinium
catenatum has relatively resistant cell walls, making it
possible to examine fossil records in sediments. The analysis of
210
Pb-dated samples taken from Australian coastal
areas showed that the introduction of G. catenatum into
southern Tasmanian waters occurred around 1972
(Hallegraeff, 1998). Populations of G. catenatum have
been found in Australian ports since the 1990s. The
appearance of G. catenatum coincides with the start of
bulk woodchip exports from southern Tasmania to Japan.
The chemical structures of paralytic shellfish toxins
produced by geographically different populations of
G. catenatum are distinguishable from each other
(Oshima et al., 1993). Their structures are not affected
by temperature, salinity, or nitrate and phosphate concentrations in the culture medium. The major toxins, which
have the N-sulfocarbamoyl group as a substituent and
were produced by the species isolated in 1986 and
1988 from Tasmania, Japan, and the Galicia region of
Spain, were C1 to C4 toxins as well as gonyautoxins
5 and 6. Only the Australian population produced the
novel 13-deoxydecarbamoyl toxins.
Accumulated mutations in rDNA are known to
reflect the prolonged geographic isolation and independent evolution within the region. Genetic analyses of
the toxic dinoflagellates Alexandrium tamarense and
A. catenella were made based on rDNA sequences and
were applied to the interpretation of the biological invasion pathway. The small and large subunit rDNA
sequences show the genetic diversity of A. tamarense
and A. catenella living in Japanese coastal areas
(Scholin et al., 1995). One possible thought is that the
Eastern Asian species was contaminated with the Western European species prior to the 1970s, and diverse
populations taken at ports of call in the Asian region were
introduced into Australian waters via unloaded ballast
water around the 1970s.
Survivability of pathogenic Vibrio cholerae
in environments
Cholera is an epidemiologic syndrome caused by
V. cholerae. The pathogenesis is classified into two groups
based on the serogroups of O1 and O139 (Kaper et al.,
1995). Furthermore, V. cholerae O1 is classified into two
biotypes, classical and El Tor. The seventh pandemic of
cholera, caused by V. cholerae O1 of the El Tor biotype,
has been experienced since 1961 in locations around the
world.
V. cholerae can exist in metabolically inactive states
during which the cultivability of dormant cells declines
but remains alive. The cells in such a “viable but
nonculturable” state are thought to enhance survivability
under harsh conditions. As for the process of becoming
active following dormancy, a recent study on the germination of Bacillus subtilis spores suggests that cell wall
muropeptides released from growing cells serve as the signal molecules for the initiation of growth (Dworkin and
Shah, 2010).
V. cholerae of O1 and O139 serogroups were detected
in more than 93 % of ships (n ¼ 15 ships) calling at ports
in Chesapeake Bay, USA (Ruiz et al., 2000). The numbers of V. cholerae cells having the O1 and O139 antigens in seawater samples were orders of 10
5 and 10
4
colony-forming units (CFU) liter
À1 , respectively.
Although their percentages were approximately 1 %
compared with the total number of cells detected in the
seawater (n ¼ 7 ships), both serotypes had adhered onto
plankton samples. The results indicate that pathogenic
V. cholerae have continuously dispersed into coastal
areas with discharged ballast water, increasing the risk
of human infection with cholera.
Estimation of survivability of V. cholerae in Tokyo
Bay following discharge with ballast water
More than 5,900 overseas vessels have arrived in Tokyo
Bay in recent years. It is natural to assume that large
amounts of ballast water containing pathogenic
V. cholerae have been discharged in the area. Mimura
and Miwa (2013) counted the total population of
colony-forming marine vibrios in samples taken in
Tokyo Bay. The numbers of non-sucrose-metabolized
and sucrose-metabolized vibrio populations on
thiosulfate-citrate-bile salt-sucrose agar plates were less
than 10
4.0 and 10
2.0 CFU ml
À1
, respectively, for all of
the samples (n ¼ 6) (Figure 1). No population that could
make colonies at 37
C was obtained on the plates, and
the population of sucrose-metabolized marine vibrios
was less than 0.16 % of the total bacterial populations
for all of the samples taken in Tokyo Bay.
The estimation of survivability of V. cholerae after dispersal into the coastal area in Tokyo Bay was carried out
using Vibrio sp. as a substitute strain of the pathogenic
V. cholerae (Mimura and Miwa, 2013). The isolate used
in the experiment has physiological and biochemical similarities with those of the pathogen, i.e., they can grow in
37
C and metabolize sucrose as a carbon source
(Mimura et al., 2005). Seawater samples were taken from
Tokyo Bay from June 2009 to March 2010. When the cells
on orders of 10
3 and 10
4 CFU ml
À1 were added to raw seawater samples that had different numbers of native
populations of 10
3.5
–10
6.1 CFU ml
À1 (n ¼ 6 seawater
samples), it was confirmed that no Vibrio sp. cells
survived 2 weeks of incubation at given temperatures,
except in one instance. In the sample in which Vibrio
sp. cells survived, the number of surviving 10
1.6 CFU
ml
À1 out of the initially added 10
3.7 CFU ml
À1 was
obtained under competition with the native population of
MICROBIAL SURVIVABILITY
435