These fungi grow as saprophytes, parasites, or both by using specific proteolytic, glycolytic, or lipolytic enzymes to extracellularly break down substrates and to absorb the products of digestion through the fungal cell envelope. The fungal cell wall gives shape and form, protects against mechanical injury, prevents osmotic lysis, and provides passive protection against the ingress of potentially harmful macromolecules. Filamentous Fungi and Filamentous Bacteria Fungi are different from the Actinomycetes, a group of prokaryotic filamentous bacteria having peptidoglycans in their cell walls and an absence of nuclear membranes and organelles, but the two groups of microorganisms are usually considered together in texts. Hyphal wall and yeast cell wall polysaccharide synthetases are active at sites where growth is occurring and inactive when no growth is occurring.
Morphogenesis is a balance between wall synthesis and wall lysis.
Asexual Reproduction Asexual reproduction occurs via division of nuclei by mitosis. With the absence of meiosis, other mechanisms associated with the nuclear cycle result in recombination of hereditary properties and genetic variation. The molds, for example, are a large group of microscopic fungi that include many of the economically important plant parasites, allergenic species, and opportunistic pathogens of humans and other animals. They are characterized by filamentous, vegetative cells called hyphae. The septum, however, still provides for cytoplasmic communication, including intercellular migration of nuclei.