THE RUMEN ANAEROBIC FUNGI : COLONIZERS OF PLANT FIBRE

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Submitted on 1 Jan 1979

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THE RUMEN ANAEROBIC FUNGI : COLONIZERS OF PLANT FIBRE

T. Bauchop

To cite this version:

T. Bauchop. THE RUMEN ANAEROBIC FUNGI : COLONIZERS OF PLANT FIBRE. Annales de

Recherches Vétérinaires, INRA Editions, 1979, 10 (2-3), pp.246-248. �hal-00901141�

THE RUMEN ANAEROBIC FUNGI : COLONIZERS OF PLANT FIBRE

T. BAUCHOP

Applied Biochemistry Division, DSIR, Palmerston North, New Zealand.

Large

numbers of anaerobic

phycomyce-

tous

fungi

^colonize

plant fragments

^{in the}

rumen of cattle and

sheep feeding

^{on fibrous}

diets

(Bauchop, 1979a,

b). The

magnitude

^of

this rumen flora has so far been overlooked

(Orpin,

^{1977). It} has been routine

practice

ⁱⁿ

microbiological

^{studies to strain rumen con-}

tents and discard the « solids » fraction. It is within the « solids » fraction that the rumen

anaerobic

fungi

^{are to be found.}

Digestion

of cellulose and related

plant

fibrous materials

by

^rumen microbes is central to ruminant nutrition.

By

^{means of}

scanning

electron

microscopy

(SEM) details were

sought

^{of the}

micro-organisms

^associated

with fibrous

plant fragments

^{in the rumen.}

Methods of

preparation

^of

samples

^{for SEM}

examination are described elsewhere (Bau-

chop,

^1979b).

In each

study

where animals consumed

high

amounts of

fibre, large

numbers of

fungi

^were

found attached to stem

fragments

^{taken at}

randon from rumen contents of

sheep

^or

cattle.

Highest populations

^{were found with}

stalky,

^fibrous

diets,

e.g. chaffed lucerne

(Medicago

^{sativa L.) in}

sheep (fig. 1),

^and meadow

hay

in cattle

(fig.

^2).

High popula-

tions of

fungi

^{were also}

present

^{in the rumen} of animals

grazing stalky

pastures : ^{in cattle}

feeding

^{on pasture of}

predominantly perennial

ryegrass (Lolium perenne

L.),

and in

sheep grazing

pure

perennial

ryegrass. Lower popu- lations of

fungi

^were present ^{in the rumen of}

sheep grazing stalky,

pure lotus (Lotus

pedun-

culatus L.l. ).

Anaerobic

fungi

^{were not} detected in rumen contents of

sheep grazing soft, leafy diets,

low in

fibre,

e.g.

continously grazed

pasture ^that had no

opportunity

^to

develop

^{stalks or see-}

dheads,

^or pure stands of young

lucerne,

^red clover (Trifolium pratense L.l ^or white clover ITrifolium _repens L.l. /.

Fungi principally

^{colonized stems. In}

legu-

mes, colonization was

mainly

^at

regions

^of

epi-

dermal

damage.

With grasses

fungi

^were

found

chiefly

^on the inside surface of the hol- low stems. Leaves were colonized

principally

in area close to vascular bundles. Stomatal

invasion,

^{found in some} leaf

samples,

^{was of}

minor

significance.

Details of

fungal

colonization of feed mate- rials were

investigated.

^{Pieces of stem or}

leaf, suspended

ⁱⁿ

nylon bags

^{in the rumen of cattle}

or

sheep

fed fibrous

diets,

^were colonized

rapidly by fungal

zoospores.

Following

^attach-

ment of _zoospores to

plant surfaces, flagellae

detached within a few minutes.

By

^{2-3 h}

large

numbers of

fungi

^were attached. Invasion

by fungal hyphae

^was demonstrated most

readily

in leaf. In

experiments

with wheat straw

leaf, by

³

h, hyphae

^were detected in

mesophyll

^tis-

sue.

Subsequent fungal proliferation

^resulted

in

development

^{of an} extensive rhizoid («

mycelium ? ). Development

^of

sporangia

commenced at c. 12 h and

by

^{c. 24 h had}

grown to mature size. The

fungal life-cycle

recommenced with release of zoospores from

sporangia.

Development

^of

fungal

^{rhizoid was obser-}

ved in

plant fragments,

^{both in rumen}

digesta

and in anaerobic cultures.

Evidence for extensive

digestion

^of

plant

material

by fungi

^has been obtained in cultu-

res. With wheat straw leaf the extent of rhi- zoid

development corresponded closely

^with

areas of extensive

digestion (fig.

^3).

Fungal

cellulase was demonstrated in cultures contai-

ning strips

of filter paper. The rumen

phycomycetes

grew ^as distinct colonies and the paper ^was

digested

^{in the area} of colonial

development. Degradation

^{of the hard}

fibre, sisal,

^{also was obtained in culture.}

Gut anaerobic

phycomycetous fungi

^have

now been found to occur in several herbivo-

rous animals

consuming high

fibre diets. Simi- lar

fungi

^were found attached to

plant

^mate- rials from the rumen of feral red

deer,

^reindeer

and

impala.

Six

species

^of

macropod

^marsu-

pials,

^the

kangaroo tribe,

also had similar

fungi

attached to

plant fragments

^{obtained from}

their ruminant-like stomachs. In two

examples

of herbivores

possessing

^a

major

fermentation in the hind gut, the horse and the African ele-

phant, large

numbers of anaerobic

fungi

^were

found

colonizing plant

material in fresh faecal

samples. Fungi

from both of these latter sour- ces were cultured

anaerobically.

There has been considerable confusion con-

cerning

^the

life-cycle

^{of the anaerobic}

phycomycetes

^{in the} rumen ; this has ^now been resolved. It must be

appreciated

^that

these

fungi

^attach

rapidly, invade,

^and

develop

on solid substratum.

Eventually they

^{are found}

attached to the

fibrous, refractory plant

^frac-

tions that turn over

slowly

^{in the} rumen,

although they

also invade associated softer

plant

tissues: The most fibrous diets suppor- ted the

greatest populations

^of

fungi.

^The

fungi

^{are not} found in the rumen of

sheep ingesting mainly soft, leafy, plants

^{as the tur-}

nover time of such materials is too

short ;

^the

complete life-cycles

^{of the}

fungi require

^{c. 24}

h.

The

quantity

^of

fungal

^rhizoid

tissues,

and their

enzymic activities,

^{holds the}

key

^{to asses-}

sing

^the

importance

^{of these}

fungi

^{in the}

rumen

fermentation. However,

^{the extent of}

attachment, colonization,

and

growth

^on

fibrous

plant fragments suggests

^a

significant

role in fibre

digestion

^{in the} rumen,

perhaps

^as

initial colonizers in

ligno-cellulose digestion.

Moreover,

the broad distribution of anaerobic

fungi

ⁱⁿ

widely differing

herbivores indicates that

they

^{are well}

adapted

^{to the}

gut

^environ-

ment and suggests ^that

they

^are

important.

Acknowledgements

I am indebted to Dr R.T.J. Clarke for discus- sion.

References

BAUCHOP T., 1979a. Rumen Anaerobic Fungi. Abstr. Ann. Mtg. ^{Amer. Soc.} Microbiol. (in press).

BAUCHOP T., 1979b. Rumen Anaerobic Fungi ^of Cattle and Sheep. Appl. Enivron. Microbiol. 37 (in press).

ORPIN C.G., 1977. The Occurrence of Chitin in the Cell Walls of the Rumen Organisms Neocallimastix fron-

talis, Piromonas communis and Sphaeromonas communis. J. gen. Microbiol. 99, 215-218.