Given their internal cellular structure, sclerotia are believed to act in a manner similar
to artificial microbial carrier substrates.
Analyzing the composition of the microbial community inside sclerotia collected
from soil will enable us to evaluate the relationship between sclerotia and microorganisms in soil ecosystems. Furthermore, observing the colonization of autoclaved
sclerotia by microorganisms will enable us to investigate the attachment of microorganisms to sclerotia under controlled conditions in the absence of other biological
factors. These investigations are expected to provide insight that will facilitate the
design of novel carrier substrates. In addition, investigation of the carrying capacity
of sclerotia and the bacterial colonization rate will yield basic information that will
be useful for controlling the establishment of microbial agents in carrier substrates.
In this study, we reviewed studies designed to evaluate the effectiveness of
sclerotia as microbial carrier substrates by investigating the microbial community
inside sclerotia collected from soil and measuring the ability of bacteria to colonize
autoclaved sclerotia, with the goal of obtaining basic information that can be used to
design novel microbial carrier substrates. Using a culture method, we analyzed the
microbial communities inside four sclerotia collected from soil. In addition, we
tested the ability of eight bacterial species isolated from the inside of sclerotia to
recolonize autoclaved sclerotia.
4.2 Bacterial Habitat in Sclerotia Grains
Porous materials such as charcoal and ceramic balls are the major microbial carriers
used to maintain the activities of useful microbes in remediation of wastewater and
soils. Charcoal and ceramic balls are non-nutritional carriers, whereas crab shell is a
type of nutritional carrier, composed of chitin and chitosan.
The sclerotia grains discussed in this chapter are frequently found in acidic forest
soils. They appear as black spheres measuring 0.1 to 5 mm in diameter, with a
cellular structure (chamber diameter: 3–15 μm). Adjacent “cells” are connected via
septal pores ranging in size from 0.2 to 0.8 μm. As shown in Fig. 4.1, bacteria
harbored inside the cells of a sclerotium are commonly observed by scanning
electron microscopy. Assuming that the diameter of the sclerotium pictured in
Fig. 4.1 and the hollow part at its center are 1 mm and 0.6 mm, respectively, then
the space occupied by the sclerotial cells is calculated as about 0.41 mm
3 . Assuming
the volume of one sclerotial cell as 6 Â 6 Â 6 μm ¼ 216 μm
3 , we can calculate that
the sclerotium contains approximately 1.9 million (10
6 ) cells. Because around
10 bacteria can be observed in one cell, the number of bacteria inhabiting the
sclerotium grain can be estimated as 1 Â 10
7 .
4 Sclerotia Grains as Bacterial Carriers in Soil
65
to artificial microbial carrier substrates.
Analyzing the composition of the microbial community inside sclerotia collected
from soil will enable us to evaluate the relationship between sclerotia and microorganisms in soil ecosystems. Furthermore, observing the colonization of autoclaved
sclerotia by microorganisms will enable us to investigate the attachment of microorganisms to sclerotia under controlled conditions in the absence of other biological
factors. These investigations are expected to provide insight that will facilitate the
design of novel carrier substrates. In addition, investigation of the carrying capacity
of sclerotia and the bacterial colonization rate will yield basic information that will
be useful for controlling the establishment of microbial agents in carrier substrates.
In this study, we reviewed studies designed to evaluate the effectiveness of
sclerotia as microbial carrier substrates by investigating the microbial community
inside sclerotia collected from soil and measuring the ability of bacteria to colonize
autoclaved sclerotia, with the goal of obtaining basic information that can be used to
design novel microbial carrier substrates. Using a culture method, we analyzed the
microbial communities inside four sclerotia collected from soil. In addition, we
tested the ability of eight bacterial species isolated from the inside of sclerotia to
recolonize autoclaved sclerotia.
4.2 Bacterial Habitat in Sclerotia Grains
Porous materials such as charcoal and ceramic balls are the major microbial carriers
used to maintain the activities of useful microbes in remediation of wastewater and
soils. Charcoal and ceramic balls are non-nutritional carriers, whereas crab shell is a
type of nutritional carrier, composed of chitin and chitosan.
The sclerotia grains discussed in this chapter are frequently found in acidic forest
soils. They appear as black spheres measuring 0.1 to 5 mm in diameter, with a
cellular structure (chamber diameter: 3–15 μm). Adjacent “cells” are connected via
septal pores ranging in size from 0.2 to 0.8 μm. As shown in Fig. 4.1, bacteria
harbored inside the cells of a sclerotium are commonly observed by scanning
electron microscopy. Assuming that the diameter of the sclerotium pictured in
Fig. 4.1 and the hollow part at its center are 1 mm and 0.6 mm, respectively, then
the space occupied by the sclerotial cells is calculated as about 0.41 mm
3 . Assuming
the volume of one sclerotial cell as 6 Â 6 Â 6 μm ¼ 216 μm
3 , we can calculate that
the sclerotium contains approximately 1.9 million (10
6 ) cells. Because around
10 bacteria can be observed in one cell, the number of bacteria inhabiting the
sclerotium grain can be estimated as 1 Â 10
7 .
4 Sclerotia Grains as Bacterial Carriers in Soil
65