Zoosporic fungi: Chytridiomycota Kingdom Fungi

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Zoosporic fungi Chytridiomycota Kingdom Fungi
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• Chytridiomycota Zygomycota
• sometimes referred to as lower fungi
• formerly classified in the Phycomycetes algal
  fungi
• thought to have evolved from algae via the loss
  of
• chloroplast no longer excepted theory
• Chytridiomycota and the rest of Kingdom Fungi
  are
• more closely related to animals via protozoan
• ancestor (e.g., choanoflagellates)

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A
SCOMYCOTA
C
ROWN
F
UNGI
B
ASIDIOMYCOTA
G
LOMALES (ZYGOMYCOTA)
KINGDOM
F
UNGI
ZYGOMYCOTA
(M
UCORALES
,
E
NTOMOPHTHORALES
, T
RICHOMYCETES
)
B
LASTOCLADIALES
)
(CHYTRIDIOMYCOTA
M
ONOBLEPHARIDALES
(
CHYTRIDIOMYCOTA
)
C
HYTRIDIALES
, N
EOCALLIMASTIGALES
,
S
PIZELLOMYCETALES
(
CHYTRIDIOMYCOTA
)

M
ICROSPORIDIA ?
O
UTGROUPS
(C
HOANOFLAGELLATES, METAZOA)
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Chytridiomycota

• General characteristics
• only flagellated members of the Kingdom
  Fungi
• chitin cell walls
• flattened mitochondrial cristae
• AAA lysine biosynthesis
• ergosterol
• glycogen

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• Ecology
• aquatic terrestrial
• most species are saprobes
• some parasites of protists, invertebrates, fungi
  plants
• some anaerobic species in the rumen of
  herbivores
• recently discovered pathogen of amphibians

www.fdrproject.org/pages/disease.htm
Batrachochytrium dendrobatidis
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• Thallus and life history diversity
• holocarpic - entire thallus converted into a
  sporangium
• eucarpic - portions of thallus converted into
  sporangia
• development of vegetative thallus

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• unicellular - may produce rhizoids that mainly
• serve to anchor thallus rhizoids lack nuclei
• filamentous - coenocytic mycelium septa may
  form
• at base of reproductive structures

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• endobiotic - living entirely within the cells of
  their hosts
• epibiotic - producing sporangia on the surface
  of either
• a living host or dead organic

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• Flagellated stages of life cycle
• zoospores - asexual reproduction
• planogametes - sexual reproduction (not all
  species)
• both zoospores planogametes possess a single,
• posterior whiplash flagellum

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• Asexual reproduction
• initiates with zoosporangium filled with
  protoplasm
• and many nuclei
• protoplasm of zoosporangium is incorporated into
• numerous zoospores may involve vesicle formation
  
• zoospores are released, swim, encyst, then
  germinate
• to produce a thallus

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• operculate zoosporangia form a well-defined
  circular cap,
• operculum, through which the zoospores emerge
• inoperculate zoosporangia discharge zoospores
  through
• a discharge tube, formed when papilla dissolves
• most known species possess inoperculate
  zoosporangia

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• Sexual reproduction
• Modes of sexual reproduction
• Planogametic copulation (three forms)
• isogamous
• anisogamous
• nonmotile egg fert. by a motile antherozoid
• Gametangial copulation
• tranfer of protoplast from one gametangium to
  another
• Somatogamy
• fusion between rhizoidal filaments

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• Life cycles
• haplobiontic - one free living thallus
• haploid (haplobiontic-haploid)
• diploid (haplobiontic-diploid)
• diplobiontic - alternation of generation
  haploid thallus
• alternates with a diploid thallus
• Chytridiomycota - examples of both
• haplobiontic-haploid (e.g., Chytridium) zygotic
  meiosis
• diplobiontic (e.g., Allomyces) sporangial meiosis

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• Zoospores
• cornerstone of ordinal classification
• five zoospore types
• basis for ordinal groupings
• single whiplash flagellum, rarely polyflagellate
  cells
• attached and directed posteriorly

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Zoospores (cont.)

• organelles
• mitochondria, microbodies, endoplasmic reticulum,
  and
• one to many lipid bodies located in specific
  regions
• some possess microbody-lipid globule complex
  (MLC)
• gamma particle
• unique to chytrid zoospores
• small membrane-bound organelle containing an
• electron-opaque, cup-shaped inclusion
• protein storage (?)

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• Flagellar apparatus
• flagellum
• kinetosome
• (basal body, flagellated centriole)
• dormant kinetosome
• (nonfunctional centriole or nfc)
• flagellar roots

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• Microbody-lipid globule complex
• (MLC)
• assemblage of organelles
• lipid bodies in association with
• microbodies
• mitochondria
• membrane cisternae
• or rumposomes
• not all chytrids have well
• organized MLC
• functions in utilization of stored
• lipid and regulation of calcium

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Orders of Chytridiomycota Chytridiales Spizellomy
cetales Blastocladiales Monoblepharidales Neocalli
mastigales
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Chytridiales true mycelium lacking rhizoids or
rhizomycelium present in some species
Blyttiomyces
Chytridium
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Spizellomycetales mainly isolated from soil some
are parasites of other fungi and algae
Piromyces
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Blastocladiales most advanced group (?) mycelial,
highly organized zoospores, male and female
gametangia, diplobiontic
Allomyces
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Monoblepharidales oogamous anisogamous
reproduction Foamy mycelium
Monoblepharella
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Neocallimastigales advanced group obligate
anaerobes in rumen hindgut of herbivores
zoospores uni- to polyflagellated
Neocallimastix
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Life Cycles to Review Blastocladiales (pages
109) Allomyces macrogynus
alternate generations, anisogamy
Monoblepharidales (page 119)
Monoblepharis polymorpha nonmotile
egg Chytridiales (page 105) Chytriomyces
hyalinus rhizoidal somatangy
operculate Rhizophidium couchii
gametangial inoperculate