the lateral branches spread. However, in the case of deep soil
plowing, the roots reach 40 cm in depth and the plant tolerates drought. Therefore, land which has a deep surface soil
layer and good drainage should be suitable for cultivating
cucurbitaceous yugao. Due to the fact that the southern part
of Tochigi Prefecture is covered by soil of the Kanto loam
layer, which has good drainage and a light weight, cucurbitaceous yugao roots can grow well there. As this is an
inland area, the temperature tends to be higher and evening
rain showers often occur in midsummer, thus providing the
necessary temperature and rainfall required for growing
cucurbitaceous yugao. Due in part to the suitable soil and
weather conditions, the cultivation of cucurbitaceous yugao
became popular in the area.
Mature fruits of the cucurbitaceous yugao which have
reached the size mentioned above are harvested in the early
morning from July to August. Harvested fruits are immediately set on a lathe-like machine; after removing the skin
with the edge of a blade, the pulp is then peeled to produce a
long, thin belt (3 cm in width, 3 to 4 mm in thickness, 2 m
in length). The peeled fruit belts are then hung on a pole
outside or inside a hothouse to dry. Most farmers start to
harvest the fruits before dawn in order to finish the harvesting early and allow more time for drying. In order to
avoid the oxidation-browning of kanpyo, dried kanpyo belts
are normally fumigated with sulfur dioxide prior to packing.
7.5.2 New Aspects on Nitrifying
Microorganisms
Nitrification is a process that is performed by
ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing
bacteria (NOB). Ammonia oxidation is the first step of
nitrification. Since the presence of ammonia-oxidizing
archaea (AOA) was confirmed in 2005, these organisms
are always found to be present in various natural environments, and it is clear that the contribution of AOA to nitrification is very large.
We here describe the new findings and topics regarding
nitrifying microorganisms that were clarified in Japanese soil
environments over the past decade; we present studies that
target soil, compost, and coastal soil environments.
In non-cultivated soil, Onodera et al. (2010) revealed the
seasonal variation of the vertical distribution and nitrification
activity of the AOA and AOB in temperate forest soil. They
suggested that AOB contributed to the net nitrification of the
top layer of such soil.
Fujii et al. (2010) investigated the annual fluctuations in
the abundance of AOB and AOA living in paddy field soil
and the number of bacteria in both groups. A difference in
the seasonal variation was shown. They suggested that in
Japanese paddy field soil there was difference in the
succession of abundances between the amoA genes of AOB
and AOA.
Hayatsu et al. (2017) isolated an acid-adapted AOB from
acidic agricultural soil. This strain, TAO100, belongs to the
Gammaproteobacteria class, and the optimum pH for its
growth was found to be pH 5.0–7.5. However, TAO100
survived under highly acidic conditions (down to pH 2) by
forming agglomerates and was not halophilic phenotypically. The authors proposed TAO100 as a novel species of a
new genus, Candidatus Nitorosoglobus terrae.
Yamamoto et al. (2010) investigated the relative diversity
and abundance of AOB and AOA in cattle manure composting. They revealed a change in AOB community structure during composting by denaturing gradient gel
electrophoresis analysis and real-time PCR. The results
showed that both AOB and AOA played active roles in
nitrification in the composting system.
Yamamoto et al. (2011) also analyzed the dynamics of an
archaeal community during composting. Their results
revealed that the methanogenic archaea and AOA may be
the dominant microorganisms in the composting process. In
their analysis of the archaeal amoA gene, the dominant amoA
gene sequence showed 99% homology with Candidatus
Nitrososphaera gargensis. These results suggest that in the
composting procedure, AOA, may play a role in ammonia
oxidation in spite of the high ammonia concentration.
Nakagawa and Takahashi (2015) isolated AOB that were
tolerant to high ammonia concentration from composted
cattle manure. The isolated strain belongs to the genus
Nitrosomonas and grew at a high ammonium concentration
of 1000 mM. The authors proposed a provisional taxonomic
assignment of Nitrosomonas stercoris and registered the
strain as a new species.
Ando et al. (2009) investigated the number of bacteria
and nitrification activity in the bottom sand of an eelgrass
zone in Tanoura Bay, Shizuoka, Japan. They observed a
seasonal change in the abundance of AOA and AOB derived
from the sand. These results suggest that these microorganisms contributed to nitrification in the sediment of the
eelgrass zone.
Matsutani et al. (2011) highly enriched a new marine
ammonia-oxidizing crenarchaeote from the coastal sand of
the eelgrass zone. This strain (NM25) belonged to Candidatus Nitrosopumilus and grew in an ammonium concentration of 15 mM in a medium, and showed the existence of
AOA adapted to an environment with a high ammonium
concentration.
Ishii (2017) enriched AM1 strains from the coastal sand
in an eelgrass zone and examined their physiological characteristics; the AM1 were non-marine cold-adapted NOB
belonging to the genus Nitrotoga. The abundance of AM1
increased to about 80% of the total bacterial population, and
AM1 was the only detectable NOB in the bacterial
7 Kanto-Koushinetsu Region
267
plowing, the roots reach 40 cm in depth and the plant tolerates drought. Therefore, land which has a deep surface soil
layer and good drainage should be suitable for cultivating
cucurbitaceous yugao. Due to the fact that the southern part
of Tochigi Prefecture is covered by soil of the Kanto loam
layer, which has good drainage and a light weight, cucurbitaceous yugao roots can grow well there. As this is an
inland area, the temperature tends to be higher and evening
rain showers often occur in midsummer, thus providing the
necessary temperature and rainfall required for growing
cucurbitaceous yugao. Due in part to the suitable soil and
weather conditions, the cultivation of cucurbitaceous yugao
became popular in the area.
Mature fruits of the cucurbitaceous yugao which have
reached the size mentioned above are harvested in the early
morning from July to August. Harvested fruits are immediately set on a lathe-like machine; after removing the skin
with the edge of a blade, the pulp is then peeled to produce a
long, thin belt (3 cm in width, 3 to 4 mm in thickness, 2 m
in length). The peeled fruit belts are then hung on a pole
outside or inside a hothouse to dry. Most farmers start to
harvest the fruits before dawn in order to finish the harvesting early and allow more time for drying. In order to
avoid the oxidation-browning of kanpyo, dried kanpyo belts
are normally fumigated with sulfur dioxide prior to packing.
7.5.2 New Aspects on Nitrifying
Microorganisms
Nitrification is a process that is performed by
ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing
bacteria (NOB). Ammonia oxidation is the first step of
nitrification. Since the presence of ammonia-oxidizing
archaea (AOA) was confirmed in 2005, these organisms
are always found to be present in various natural environments, and it is clear that the contribution of AOA to nitrification is very large.
We here describe the new findings and topics regarding
nitrifying microorganisms that were clarified in Japanese soil
environments over the past decade; we present studies that
target soil, compost, and coastal soil environments.
In non-cultivated soil, Onodera et al. (2010) revealed the
seasonal variation of the vertical distribution and nitrification
activity of the AOA and AOB in temperate forest soil. They
suggested that AOB contributed to the net nitrification of the
top layer of such soil.
Fujii et al. (2010) investigated the annual fluctuations in
the abundance of AOB and AOA living in paddy field soil
and the number of bacteria in both groups. A difference in
the seasonal variation was shown. They suggested that in
Japanese paddy field soil there was difference in the
succession of abundances between the amoA genes of AOB
and AOA.
Hayatsu et al. (2017) isolated an acid-adapted AOB from
acidic agricultural soil. This strain, TAO100, belongs to the
Gammaproteobacteria class, and the optimum pH for its
growth was found to be pH 5.0–7.5. However, TAO100
survived under highly acidic conditions (down to pH 2) by
forming agglomerates and was not halophilic phenotypically. The authors proposed TAO100 as a novel species of a
new genus, Candidatus Nitorosoglobus terrae.
Yamamoto et al. (2010) investigated the relative diversity
and abundance of AOB and AOA in cattle manure composting. They revealed a change in AOB community structure during composting by denaturing gradient gel
electrophoresis analysis and real-time PCR. The results
showed that both AOB and AOA played active roles in
nitrification in the composting system.
Yamamoto et al. (2011) also analyzed the dynamics of an
archaeal community during composting. Their results
revealed that the methanogenic archaea and AOA may be
the dominant microorganisms in the composting process. In
their analysis of the archaeal amoA gene, the dominant amoA
gene sequence showed 99% homology with Candidatus
Nitrososphaera gargensis. These results suggest that in the
composting procedure, AOA, may play a role in ammonia
oxidation in spite of the high ammonia concentration.
Nakagawa and Takahashi (2015) isolated AOB that were
tolerant to high ammonia concentration from composted
cattle manure. The isolated strain belongs to the genus
Nitrosomonas and grew at a high ammonium concentration
of 1000 mM. The authors proposed a provisional taxonomic
assignment of Nitrosomonas stercoris and registered the
strain as a new species.
Ando et al. (2009) investigated the number of bacteria
and nitrification activity in the bottom sand of an eelgrass
zone in Tanoura Bay, Shizuoka, Japan. They observed a
seasonal change in the abundance of AOA and AOB derived
from the sand. These results suggest that these microorganisms contributed to nitrification in the sediment of the
eelgrass zone.
Matsutani et al. (2011) highly enriched a new marine
ammonia-oxidizing crenarchaeote from the coastal sand of
the eelgrass zone. This strain (NM25) belonged to Candidatus Nitrosopumilus and grew in an ammonium concentration of 15 mM in a medium, and showed the existence of
AOA adapted to an environment with a high ammonium
concentration.
Ishii (2017) enriched AM1 strains from the coastal sand
in an eelgrass zone and examined their physiological characteristics; the AM1 were non-marine cold-adapted NOB
belonging to the genus Nitrotoga. The abundance of AM1
increased to about 80% of the total bacterial population, and
AM1 was the only detectable NOB in the bacterial
7 Kanto-Koushinetsu Region
267