Improved endoglucanase production and mycelial biomass of some ericoid fungi
Adeoyo et al. AMB Expr
Improved endoglucanase production and mycelial biomass of some ericoid fungi
O. R. Adeoyo 0
B. I. Pletschke 0
J. F. Dames 0
0 Department of Biochemistry and Microbiology, Rhodes University , P.O. Box 94, Grahamstown 6140 , South Africa
Fungal species associated with ericaceous plant roots produce a number of enzymes and other bio-active metabolites in order to enhance survival of their host plants in natural environments. This study focussed on endoglucanase production from root associated ericoid mycorrhizal and dark septate endophytic fungal isolates. Out of the five fungal isolates screened, Leohumicola sp. (ChemRU330/PPRI 13195) had the highest relative enzyme activity and was tested along with isolates belonging to Hyloscyphaceae (EdRU083/PPRI 17284) and Leotiomycetes (EdRU002/PPRI 17261) for endoglucanase production under different pH and nutritional conditions that included: carbon sources, nitrogen sources and metal ions, at an optimum temperature of 28 °C. An optimal of pH 5.0 produced enzyme activity of 3.99, 2.18 and 4.31 (U/mg protein) for isolates EdRU083, EdRU002 and Leohumicola sp. respectively. Increased enzyme activities and improved mycelial biomass production were obtained in the presence of supplements such as potassium, sodium, glucose, maltose, cellobiose, tryptone and peptone. While NaFe-EDTA and Co2+ inhibited enzyme activity. The potential role of these fungi as a source of novel enzymes is an ongoing objective of this study.
Endoglucanase; Ericoid; Endophytic fungi; Mycelial biomass
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Introduction
The soils of temperate, boreal forests and heathlands are
characteristically enriched with a large number of soil
microbes that include ericoid mycorrhizal (ERM) and
dark septate root endophytic (DSE) fungi. Roots of
ericaceous plants harbour these fungi, conferring
eco-physiological benefits to the host (Bizabani and Dames 2015).
A mutualistic association is usually formed between the
plant family Ericaceae and related fungal members
(Cairney and Meharg 2003). Ericoid mycorrhizas are
characterized by densely packed intracellular fungal coils that
are formed in the epidermal cells of the fine hair roots
of their host plant while establishing a loose hyphal
network outside of the hair roots (Smith and Read 2008).
These thin hyphal coils within the cortical cells serve as
interfaces for nutrient exchange between the symbionts
(Vohnik et al. 2009). The primary function of the ERM
fungus is to facilitate the utilisation of organic complexes
as a source of nutrients for their host plant and in return,
the fungus acquires photosynthetic carbon from the host
for the completion of their life cycle (Pearson and Read
1975). Hymenoscyphus ericae is a major ericoid
fungus that has been extensively investigated for its ability
to grow on a variety of complex organic substrates that
include carboxymethylcellulose (CMC) (Leake and Miles
1996). ECM associations enable host plants to survive in
soils characterized by impoverished nutrient status, e.g.
acidic, nitrogen and phosphorus deficient soils (Read
1996). The fungi selected for this study were isolated
from the host plants belonging to genus Erica. The genus
Erica is a large varied taxon containing approximately
850 species (Oliver 2000). DSE fungi are conidial or
sterile ascomycetes that colonize living plant roots without
causing apparent negative effects such as tissue
disorganization (Jumpponen and Trappe 1998). Several DSE
fungi have been found to form symbiotic relationships
with their host plant (Usuki and Narisawa 2007). DSE
colonization has been identified in about 600 plant
species which represent about 320 genera and 114 families
(Jumpponen and Trappe 1998).
Enzymes of microbial origin have high
biotechnological importance in the processing of food, manufacturing
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of detergents, pharmaceutical products and in
molecular biology (Falch 1991). Extracellular enzymes are
produced by ERM and DSE fungi during utilization of soil
organic matter facilitating the degradation of organic
substrates into simpler units. Under laboratory
conditions, these extracellular enzymes are produced in liquid
media and can be assayed to quantify the concentration
of enzyme produced per millilitre of the filtrate, per
minute. In order to assess endoglucanase production in vitro,
experimental liquid medium amended with 1% CMC is
often used. This mimics the natural pattern of
production where hydrolysis of cellulose occurs as a result of
the action of cellulolytic microorganisms in soil
(Doolotkeldieva and Bobusheva 2011). Cult (...truncated)