lect

Chytridomycota

Literature: Zoosporic Fungi in Teaching and Research for illustrations of many genera.

Good internet link: http://zoosporic-fungi.dmc.maine.edu/

Kingdom Fungi

Phylum Chytridiomycota: Chitin+ and glucan; single posterior whiplash flagellum; single cell or coenocytic hypha

Importance: Primary invaders and decomposers of organic materials including chitin, keratin, cellulose, and hemicelluose

Features

Holocarpic-eucarpic

Monocentric (one center of activity) - Polycentric (more than one center- rhizomycelium).

Endobiotic, epibiotic, and interbiotic

Zoospore characteristics: MLC (microbody lipid complex), ruposome, side-body complex, nuclear cap (see pg. 93, figure 4-7 in Alexopoulos)

Classification of Chytridiomycota:

Order	Spizellomycetales	Chytridiales	Monoblepharidales	Neocallimastigales	Blastocladiales
habitat	In soil; seldom strictly aquatic	Mainly fresh water; soil as well; some marine	Aquatic; foamy mycelium	Obligate anaerobes in the rumen, hindgut, or caecum of various herbivores	Saprobes and parasites on variety of substrates; several are facultative anaerobes
Holocarpic/eucarpic		both		Posteriorly multiflagellate
Mono/polycentric	monocentric	Monocentric to polycentric	Monocentric to mycelial	both	Both and mycelial
rhizoids	blunt tip	Tapered tips	?
Lipid boides	Several	Single and lateral	Several		Several but associated with side body complex
ribosomes	dispersed	Packed in center with membrane	Aggregated around nucelus		Associated with nucleus
ruposomes	absent	Present	present	?	absent
nucleus	Associated with kinetosome	separated	Separated; striated disc with kinetosome		Associated with nucleus
Nuclear cap	Absent	Absent	Absent	Absent	Present
Side body complex	absent	absent	absent	Absent	Present
Sexual reproduction	?	Isogamous;Synchytrium endobioticum causes black wart disease of potatoes	Oogamous; assumed zygotic meiosis	?	Isogamous, anisogamous; sporic meiosis

Blastocladiales

Function of side body complex (microboides fused between lipid bodies and lipid bodies that are fused with a mitochrondion and in association with it because of the basal membrane (see Figure 2-19 of handout; and 9-19 to show a schematic diagram.

These fungi have no carbohydrate reserves but rely on lipids for stored energy.

Microbodies are of two types perioxisomes that are involved in glycolate metabolism and glyoxyzomes that are involved in photorespiration.

In Allomyces, Acetyl Co-A is produced in the sidebody complex and is converted to succinate by the enzymes located in the glyoxyzomes. Succinate is transported to the mitochrondion where it is further metabolized with ATP being produced. Since the mitochrondion is closely associated with the flagellar apparatus, the flagellar motion is caused by the release of energy at its base.

Life cycle o f Allomyces (see figure 4-17, pg. 109 in Alexopoulos)

Example of anisogamy and isomorphic alternation of generations (male and female gametes identical except for size; gametothallus and sporothallus with identical morphology); therefore an example of sporic meiosis

Resistant meiosporangia on sporothallus; mitosporangia on gametothallus.Female gametangia colorless; female gametes are colorless and sluggish; contain no alpha-carotene

Male gametangia appear orange-colored; male gametes orange are very active, swim in arcs interspersed with a jerky movement; contain alpha-carotene

Sexual reproduction is caused by an epigenetic effect since both male and females are produced on a haploid gametothallus

How do male gametes find female gametes.

Female gametes produce a hormone that is a bicyclic sesquiterpenediol (see fing 10-3 of handout); it has been called sirenin.

Acetyl Co-A produced in the side body complex is converted to farensyl pyrophosphae which in turn is converted to sirenin.

Because of the use of Acetyl-Co-A to form sirenin, the female gametes are not active; there is not as much ATP available in the mitchrondrin for flagellar motion.

However, the males are active and swim in arcs; apparently the male gametes have membrane positive receptors that respond to sirenin concentration. The response is to cut down on the length of the arc in the swimming of the male gametes. As the male gamete near the high concentration of sirenin, the arcs disappear; however the jerks become more abundant. Thus the male gametes are very erratic and active near the female gametes and this reponse insures syngamy.

Coelomomyces

Life Cycle: see figure 4-20 on pg. 115 in Alexopoulos.

Obligate parasite of mosquito larvae and various flies. Whisler at U. of W determined life cycle.

Heteroecious and Isomorphic Alternation of Generations with anisogamous syngamy.

Flagellated zygote attracted to and infects mosquito larva; develops sporothallus in mosquito larva; resistant sporangia are produced towards out epidethelium of larva; larva dies, resistant sporangia released; when conditions are correct, the RS produce meiospores that are attracted to and infect the copepod (Cyclops vernalis); gametothallus produced within the copepod, releases gametes and zygote production outside of copepod. Zygote attracted to mosquito larva.

Monoblepharidales

Foamy cytoplasm

Unique because it is oogamous. Has an oogonium with attached antheridium. Antherozoid attracted to Oogonium where it fertilizes the uninucleate female protoplast (the egg); zygote is formed witin the oogonium and travels out of oogonium and sits on top of oogonium. There it is converted to an Oospore.

See pictures on web page at Maine and in your textbook (pgs. 119-120).