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Chapter 9
Microbial Sporulation
and Germination
introduction
Microorganisms that are important in food normally divide by binary fission (or elongation as in
nonseptate molds). In addition, molds, some yeasts, and some bacteria can form spores. In molds
and yeasts, sporulation is associated with reproduction (and multiplication), whereas in bacteria it is
a process of survival in an unfavorable environment. In molds and yeasts, sporulation can occur by
sexual and asexual reproduction, and sexual reproduction provides a basis for strain improvement
for those that are used industrially. In bacteria, sporulation occurs through differentiation, and it
provides a means to retain viability in a harsh environment. Among the spores, bacterial spores
have special significance in foods because of their resistance to many processing and preservation
treatments used in food. Compared with bacterial spores, mold and yeast spores are less resistant
to such treatments. Spore formation in molds, yeasts, and bacteria is briefly discussed here.
Mold Spores
Molds form spores by both asexual and sexual reproduction and, on this basis, are classified as perfect or imperfect molds, respectively. 1 Molds form large numbers of asexual spores and, depending
on the type, can form conidia, sporangiospores, and arthrospores. Conidia are produced on special
fertile hyphae called conidiophores (Figure 9.1). Among the important molds in food, Aspergillus
and Penicillium species form conidia (see Figure 28.1, Chapter 28). Sporangiospores are formed
in a sack (sporangium) at the tip of a fertile hypha (sporangiospores). Mucor and Rhizopus species
are examples of molds that form sporangiospores. Arthrospores, formed by the segmentation of
a hypha, are produced by Geotrichum. An asexual spore in a suitable environment germinates to
form a hypha and resumes growth to produce the thallus. Sexual spores form from the union of
the tips of two hyphae, two gametes, or two cells. However, among the molds important in food,
sexual reproduction is rarely observed. Some examples include Mucor and Neurospora.
Chapter 9
Microbial Sporulation
and Germination
introduction
Microorganisms that are important in food normally divide by binary fission (or elongation as in
nonseptate molds). In addition, molds, some yeasts, and some bacteria can form spores. In molds
and yeasts, sporulation is associated with reproduction (and multiplication), whereas in bacteria it is
a process of survival in an unfavorable environment. In molds and yeasts, sporulation can occur by
sexual and asexual reproduction, and sexual reproduction provides a basis for strain improvement
for those that are used industrially. In bacteria, sporulation occurs through differentiation, and it
provides a means to retain viability in a harsh environment. Among the spores, bacterial spores
have special significance in foods because of their resistance to many processing and preservation
treatments used in food. Compared with bacterial spores, mold and yeast spores are less resistant
to such treatments. Spore formation in molds, yeasts, and bacteria is briefly discussed here.
Mold Spores
Molds form spores by both asexual and sexual reproduction and, on this basis, are classified as perfect or imperfect molds, respectively. 1 Molds form large numbers of asexual spores and, depending
on the type, can form conidia, sporangiospores, and arthrospores. Conidia are produced on special
fertile hyphae called conidiophores (Figure 9.1). Among the important molds in food, Aspergillus
and Penicillium species form conidia (see Figure 28.1, Chapter 28). Sporangiospores are formed
in a sack (sporangium) at the tip of a fertile hypha (sporangiospores). Mucor and Rhizopus species
are examples of molds that form sporangiospores. Arthrospores, formed by the segmentation of
a hypha, are produced by Geotrichum. An asexual spore in a suitable environment germinates to
form a hypha and resumes growth to produce the thallus. Sexual spores form from the union of
the tips of two hyphae, two gametes, or two cells. However, among the molds important in food,
sexual reproduction is rarely observed. Some examples include Mucor and Neurospora.