Från restbiomassa till protein: En studie om filamentösa svampar
Typ
Examensarbete på kandidatnivå
Bachelor Thesis
Bachelor Thesis
Program
Publicerad
2023
Författare
Bergstedt, William
Björnelf, Stina
Johansson, Cecilia
Rydberg, Cecilia
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
One of today’s greatest challenge is producing enough nutritious food for the growing population of the
world in a sustainable way. One solution could be the increased use of residual biomass. Forestry and
agriculture generate an estimated 140 gigatons of residual biomass annually globally. Some of these
residual streams can be valorized by filamentous fungi, which convert residual biomass into proteins
to produce food and animal feed. This Bachelor thesis aimed to contribute to a more sustainable
production of food by improving the growth of filamentous fungi on Spent Sulfur Liquor (SSL) with
two methods of Classical Strain Improvement (CSI) and investigated in whether fungi can grow on
other waste streams. Eight proprietary strains (mutants of CirkuleinTM) and Trichoderma reesei,
Aspergillus niger, Aspergillus nidulans and Myceliophthora thermophila were screened.
The original and mutated fungi were screened on different liquid media to determine the strains most
adapted to each media. The best strains, ranked by growth rate, were grown in shake flasks and their
dry biomass was measured. Fungi were also grown on solid media in petri dishes. Methods used for
strain development are Adaptive Laboratory Evolution (ALE) and UV mutagenesis, with the ambition
to mutate strains with a higher growth rate that can be used in large-scale industries.
The screening of the strains resulted in six strains being chosen for fermentation in shake flasks. The
largest growth, in terms of dry weight, was obtained from the strains grown on SSL. The ALE showed
a slight improvement in growth rate for one CirkuleinTM-strain while another remained unchanged.
The UV-mutagenesis resulted in a survival rate of 1-3% and one of the mutated colonies showed an
improved growth rate. The other replicates generally showed a lower growth rate than the control
groups.
From the screening on liquid media, it can be concluded that high-throughput screening is an effective
first thinning of available strains. However, fermentation in shake flasks is necessary to get a reliable
result since it ensures that the fungi are growing on the medium and not on the agar, for example.
Though the fungi grew best on SSL they also grew on the other side streams tested and it is therefore of
interest to continue investigating those. The fungi grew on two of the solid media, but their growth was
inhibited on the coffee grounds. UV mutagenesis is a method that can produce improved strains, though
a low survival rate is imperative to see change in a small sample size. ALE also procured improved
strains, however, some of the developed strains obtained an unchanged growth rate. For both of these
methods, further rounds of treatment would be necessary to obtain more efficient strains. Furthermore,
the concentrations of the SSL used in ALE should be assessed in further studies to optimize the strain
development