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Chemical composition of some Lichen species
occurring in the' N amib Desert,
South West Africa
J. J. Joubert!, P. L. Steyn 2, T. J. Britz 3 and D. C. J. Wessels 4
The protein content of three species of lichens from the Namib Desert was determined
by means of the conventional Kjeldahl technique. Of these, Parmelia hottentotta had
the higliest protein content (16,24%), followed by Omphalodium convolutum (14,42%)
and Teloschistes capensis (13,45%)~ Acid hydrolysis of thalli of the three species
yielded fructose, galactose and glucose as well as the amino sugar glucosamine. The
hydrolysate also contained a variety of amino acids.
A viva, 67 Beatrix Street, 0002 Pretoria.
Department of Microbiology and Plant Pathology, University of Pretoria, 0002 Pretoria.
Department of Microbiology, University of the Orange Free State, 9300 Bloemfontein.
Department of Botany, Umversity of the North, Private Bag X5090, 0700 Pietersburg.
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Die proteininhoud van drie ligeenspesies uit die N amib-woestyn is deur middel van die
konvensionele Kjeldahl-metode bepaal. Van die drie het Parmelia hottentotta die
hoogste proteien-inhoud gehad (16,24%), gevolg deur Omphalodium convolutum
(14,42%) en Teloschistes capensis (13,45%). Suurhidrolise van die drie spesies het
fruktose, galaktose, glukose en die "aminosuiker glukosamien opgelewer. Die hidrolisaat het ook 'n verskeidenheid amino sure bevat.
A considerable amount of work has been published on the chemical composition of
the extracellular products of lichens. The chemistry, structure, properties and distribution of these so-called ~chen substances have been treated in detail by Asahina &
Shibata (1954), Culberson (1969, 1970) and Culberson, Culberson & Johnson (1977).
Several studies have also appeared on the chemistry of carbohydrates, free amino acids
and other intraceUular products. Reference to these products has been made by
Huneck (1973), Mosbach (1973) and Hale (1974).
Huneck & Follmann (1971) reported on the occurrence of lichen substances in Teloschistes capensis (L.f.) Malme (salazinic acid, parietin) and Omphalodium convolutum Hue (norstictic acid, stictic acid, (+) - usnic acid). The findings of these and
other authors regarding the occurrence of lichen products in other species indigenous
to South West Africa are listed by Culberson (1970) and Culberson et al (1977).
Considerable lichen growth occurs in certain parts of the central and northern Namib
Desert. More information on their chemical composition seemed of interest in view
.of their role as primary producers of organic matter in such an arid environment. This
paper represents an effort to determine the total nitrogen content as well as the amino
acid and carbohydrate composition of three lichen species from the Namib .Desert.
Lichen material
All the lichens used in this investigation were obtained through the courtesy of th~.
Director, SWA Administration, Department of Nature Conservation and Tourism,
and collected by Mr. J. Jankowitz. Parmelia hottentotta Ach. (Plate 1) was f6und
approximately 35 km east of Henties Bay. Omphalodium convolutum (Plate 2) was
collected along the gravel road between Swakopmund anq Windhoek, approximately
15 km from Swakopmund. Teloschistes capensis (Plate 3) :was collected on the gravel
flats approximately 3 km north of Wlotzka's Baken.
The lichen material was thoroughly cleaned of adhering soil and rock particles.
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Plate I: Parmelia hOllentOtla Ach.
In its natural surrounding.
(Photo W. Giess )
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Plale 2: Ompha/odium COllrO/Ulum Hue.
In ilS nalural surrounding.
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Plate 3: Te/oschisles cilpellsis (L.L) Malme.
In its natural surrounding.
(Photo W. Giess)
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Amino acid and amino sugar assay
The fragmented thalli were washed in 0,5 M sodium phosphate butTer (pH 7,5) and
lyophilized. Ten mg of thallus material was hydrolyzed in 1 cm 3 6N HCI at 100°C
for 16 h in a sealed ampule. The solution was then evaporated to dryness in a rotary
flask evaporator and finally redissolved in 1 cm 3 distilled water. The pH was adjusted
to pH 8,0 with 5N NaOH. The solution was centrifuged and the clear supernatant
stored at 4°C. the solutions (0,1 cm3) were diluted with 0,9 cm 3 citrate butTer
(pH 2,2) and 0,2 cm 3 of this was used for assay on a Bio-Cal BC-200 automatic,
amino acid analyser. Resins used in the assay were of the Aminex polystyral base type
with a cross-linking of 7,5 to 8,0% divinylbenzene. The assay specifications were as.
1. Basic amino acids
Resin height
25 cm with internal diameter of 0,9 cm
Arninex AS, particle size 11,5-15,5 ~m
14 cm
- pH 5,28; 0,35N in Na ions and 0,2N NaOH
- 50°C
2. Neutral and acidic amino acids
60 cm with internal diameter of 0,9 cm
- Aminex A6, particle size 15,5-19,5 ~m
Resin height
- 54 cm
- A = pH 3,25; 0,2N in Na ions
B = pH 5,25; 0,2N in Na ions and 0,2N NaOH
- 50°C
An amino acid calibration mixture supplied by Beckman Instruments was used as
standard. This standard solution contained 1 cm 3 of 0,62N HCI with 2,50 ± 0,004
~mole of each amino acid. One cm 3 of this solution was diluted to five cm 3 and
0,2 cm 3 was applied to the colu~n, giving a final concentration of 0,1 ~mole. Due to
the low solubility of cystine it was only present in half the concentration. The amount
of each amino acid was determined by the width x height method as described in the
manual. During prolonged hydrolysis with 6N HCI, the amino sugars underwent
hydrolytic degradation. No attempt was made to correct for the hydrolytic loss of the
amino sugars or the corresponding increases in ammonia.
Analysis of the cell sugars
A modification of the method of Cato, Cummins and Smith (1970) was used for tl~e'
analysis of the cell sugars. Ten mg amounts of washed thal,li were hydrolyzed in 2 C~3'
of 2N H2S04 for two hours in a boiling water bath. When cooled, the acid walneutralized with solid barium hydroxide to a pH of 7,0. The~recipitate was removed by
centrifugation and the deposit washed with 2 cm 3 of distilled water. The supernatant
was evaporated in a water bath at 60°C. The dry residu~ was dissolved in 0,3 cm 3
distilled water. The solution at this step was clear of any remaining barium hydroxide.
One dimensional ascending thin layer chromatography wa~ performed on silica gel G
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according to Stahl (Type 60 - Merck). The solvent system ethyl acetate (65 cm 3) and
35 cm 3 isopropanol-water mixture (2:1) was used. (Akhrem & Kuznetsova, 1965).
The chromatograms were run for three hours at 5°C. Spots were visualized by
spraying with acetonic-aniline-phthalate (aniline 2,0 cm 3 ; phthalic acid 3,0 g; acetone
95 cm3 and 5 cm 3 water) followed by heating at !05°C for five minutes. One ul of
either hydrolysate of known standard was applied to the base line of chromatogram.
The relative amounts present have been arbitrarily graded as 3+, 2+, +, (+) or-,
according to the size and intensity of the spot obtained.
Nitrogen Content was determined by means of the conventional Kjeldahl method.
A conversion factor of 6,25 was used for calculating the crude protein content.
The crude protein content of the three investigated species is shown in Table 1. In all
three cases the crude protein content was unexpectedly high and compared favourably
with that of lucerne hay (17,1%) and was much higher than that of veld grass hay
(5,9%) (Van der Merwe, 1970)
According to Huneck (1973) the protein content of lichens varies between 1,6 and
11,4% of their dry weight. Some lichens, notably Peltigera canina growing in the
Himalayas may, however, contain as much as 21% protein (Subramanian &
Ramakrishnan, 1964). The range of amino acids found in the investigated liches was
similar to those found in other plants and micro~organisms, and none of the less
commonly occurring amino acids were detected. (See table 2). The highest
concentration of amino acid found was glutamic acid in the case of P. hottentotta.
There was a notable absence of cystine, hydroxy-proline and ornithine in all three
species. The absence of D-, L- or meso-diaminopimelic acid is not unexpected as this
amino acid has so far only been found in bacterial cell walls. Unfortunately tryptophan
could not be resolved by the method used and no further attemps were made to
determine the tryptophan content of the lichen thalli.
The use of the factor of 6,25 for converting Kjeldahl nitrogen into protein content,
is subject to criticism, because no attempt was made to determine whether the ratio
between nitrogen from protein, free amino acids, nucleic acids or chlorophyll was
approximately the same as that from plant material of known cO,mposition.
The usefulness of a protein depends upon its digestibility as well as its biological
value. The biological value is determined by the number and kinds of amino acids
i present in the molecule: The nearer the food protein approaches the body proteins in
: amino acid make-up, the higher will be the. biological value. (McDonald, Edwards &
j Greenhalgh, 1973). According to data on the essential amino acid composition of
. proteins for n~n-ruminants (NRC, 1973), O. convolutum was low in methionine/
; cystine, lysine, histidine and i-leucine; P. hottentotta was low in histidine, while
T. capensis was low in histidine and phenylalanine/tyrosine. Unfortunately tryptophan, which is, an essential amino acid for non-ruminants, was not assayed. The uses
of lichens by man as an, emergency ration and as part of his daily diet has i?een
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discussed by Richardson (1977). As the chances are remote that the lichen growth of
the area will be used as a food source by non-ruminant mammals no further consideration was given to this aspect.
In ruminant diets the amino acid composition is of less impo'rtance than the total
protein and carbohydrate content. The use of lichens as a food source by vertebrates
has been summarized by Richardson (1975) and Richardson & Young (1977). It'was
mentioned by Richardson (1975) that lichens preferred by reindeer were not those with
the highest protein content but the ones which contained a high proportion of complex carbohydrates. He also stated that a deer requires the equivalent of about 2 kg
of dry lichen daily. To obtain that amount an animal browses about 12 m2 of lichen
which amounts to approximately 2160 m2 of pasture every 180 days. Because of
the slow growth of lichens a particular lichen range is not ready for regrazing for 2-5
years after modest grazing. This period increases to 10-15 years after intense grazing
(Richardson, 1975).
It seems that the lichen fields of the Namib Desert are utilized by animals (springbuck
in particular) as a supplementary food source, especially during prolonged drought
periods inland (sightings by D.C.J.W.; CoetzeeI, 1978 and Loutit 2 , 1979
personal communications). The existence of such an association will hardly be
surprising in view of the universal occurrence of such relations.
Wessels, Wessels & Holzapfel (1979) reported on the relationship between two lichenfeeding Coleoptera species and Teloschistes capensis in the Namib Desert., The vast
literature that exists on such relationships has been extensively reviewed 'by Gerson
(1973) and Gerson & Seaward (1977). According to Gerson & Seaward (1977) insects, mites and mollusc constitute important components of the terrestrial fauna and
are the main lichen grazers while the Protozoa, Rotifera and Tardigrada 'belong to the
aquatic lichen-feeding fauna. The report of Wessels et al (1979) is unique in the sense
that it is the first report on the existence of such an association between members of
the terrestrial fauna and lichens from an arid region.
As no tests for digestibility were carried out nor the true protein or carbohydrate
content determined, conclusions can not be drawn regarding the usefulness of these
lichen species as a food source for animals. In view of the relationships that exist
between lichens and animals of the Namib Desert, it is intended to pursue this
aspect further, concentrating on insect-lichen relationships as research has already
been completed.
Other low-molecular compounds, such as carbohydrates are reported to be abundant:
in lichens (Aspinall, Hirst& Warburton, 1955; Lindberg, Misiorny & Wachtmeist~r,
1953). The carbohydrates and amino sugars that could be, detected in the three inyi~ti­
gated species are shown in Table 3. No attempt was madelto investigate the occtfrrence
of polyols or polyol glycosides for which lichens are n~ted. Glucose, fructose and
I Mr. F. Coetzee; Nature Conservation and Tourism, P.O. Box 51, 9000 Swakopmund.
2 Mrs. B. Loutit; c/o The Senior Game Ranger, Ugabmond, Skeleton <I:oast Park, Private Bag 5001, 9000
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galactose are known constituents of lichens after chemical hydrolysis. Doubtful
amounts of lactose could only be detected in O. convolutum. GalaCtosamine is a
known constituent of many polysaccharides, yet was not detected in any of the three
specimens analysed. Ribose was included as standiud but contrary to expectations it
was not detected. This can only be explained in-that the concentration may have been
too low to be detected.
No attempt was made to investigate the occurrence of extraceliular lichen substances.
These substances are mostly weak phenolic compounds and their physiological role
has been the subject of considerable speculation. Huneck (1973) and Mosbach (1973)
respectively discussed the nature and biosynthesis of such extracellular substances
while reference to their economic uses and possible ecological role was made by
Richardson (1975) and Vartia (1973).
TABLE I: Crude protein content of three species of Namib Desert Lichens.
% crude protein
Omphalodium convolutum
Parmelia hottentotta
Teloschistes capensis
TABLE 2: Quantitative amino acid analysis of three species of r-/amib Desert Lichens expressed as ~mol
per 10 mg of dried material.
Amino Acid
Alanine ....................
Arginine ....................
Aspartic Acid ................
Cystine ....................
Diaminopimelic Acid ..........
Glutamic Acid ...............
Glycine ....................
Histidine ....................
Hydroxyproline ..............
Leucine ....................
Lysine .....................
Methionine ..................
,Ornithine ...................
! Phenylalanine ................
Proline ......................
Serine .....................
Threonine ..................
yypt?phan .................
. Tyrosme ...................
Valine .....................
Ammonia ...................
0,25 '
2,60 I
Not assayed
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TABLE 3: Qualitative amino sugar and carbohydrate analysis of three species of Namib Desert Lichens.
Amino sugars and
Glucosamine ............... .
Galactosamine .............. .
Arabinose .................
Fructose ..................
Glucose ...................
Mannose ..................
Rhamnose .................
Galactose ..................
Lactose ................... .
Maltose ................... .
+ present in small amounts; + + present in intermediate amounts; + + + present in appreciable amounts;
(+) doubtful; - absent.
The thalli of three lichen species collected from the Namib Desert (Omphalodium
convolutum, Parmelia hottentotta and Teloschistes capensis) were analyse,d for their
crude protein content, amino acid composition of the proteins and the sugar composition of the carbohydrates.
The crude protein content, calculated from the total nitrogen content as determined
by means of the conventional Kjeldahl method, was found to be unexpectedly high in
all three cases (14,42% for O. convolutum, 16,24% for P. hottentotta and 13,45%
for the T. capensis.) The amino acid composition of the thallus proteins was determined by means of an automatic amino acid analyser after acid hydrolysis. The range
of amino acids found was similar to those found in higher plants and micro-organisms,
and none of the less commonly occurring amino acids was d~tected. The highest concentration of amino acid found was that of glutamate in P. hottento tta. Ther~ was
a notable absence in all three cases of cystine, hydroxy-proline and ornithine. The
digestibility of the thalli by ruminants as well as non-ruminants was not determined
accordingly, no conclusions could be drawn regarding the usefulness of the lichen
thalli as a food source.
Carbohydrates were analysed. by acid hydrolysis and thin layer chromatography.
Fructose and glucosamine were detected in all three species, the former in appresJable
amounts. Glucose was detected in only two of the three bases, whereas galactose and
lactose were found in only one species.
Reference has also been made to the role of lichens
the area.
Plates of the three lichen species are presented.
afood source for animals in
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The authors are indebted to the Director, SWA Administration Department of Nature
Conservation and Tourism for supplying the material and to their respective institutions for financial assistance.
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