Identification of a cellulolytic active fungal strain, isolated from a cigarette waste microenvironment, showing preference for growth on cellulose acetate
Date
2020-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Globally, environmental pollution such as greenhouse gases and microplastics are ubiquitous
throughout nature. Long-term negative environmental effects and bioaccumulation of
anthropogenic compounds within the food-chain is widely reported. Cigarette filters are the
single most littered item with over 4 trillion smoked cigarette filters entering the environment
every year. Studies estimate that over 66 % of smokers incorrectly dispose of their cigarette
filters culminating to a total annual of 750 million kg of pollution. The fate of an incorrectly
discarded cigarette filter causes damage in two major manners. Firstly, a smoked cigarette filter
acts as a vector for a myriad of toxic compounds and heavy metals. Secondly, cigarette filters
are made of 15 000 or more cellulose acetate fibers linked together by glycerol triacetate.
Throughout the degradation process, these toxic compounds and microscopic cellulose acetate
fibers leach into the environment. Cigarette filters mostly enter the environment through
sewerage and drain water systems that enter into the ocean. Consequently, chemically derived
cellulose has been reported covering over 2 billion km2 of the ocean seabed contributing to the
microplastic deep sea sink and marine microplastic epidemic. Research on cigarette filter
degradation indicates that after five years, depending on the environment, the total mass loss
can range between 50 – 80 %. Estimates suggest that a cigarette filter can remain within the
environment for up to ten years. The continual deposition of cigarette filters within the
environment highlights the necessity for recycling solutions and effective waste management
of cigarette filters.
A cigarette bin could serve as a genetically resourceful environment, where the microbial
community partake in a synergistic process for the degradation of cigarette filters. This study
centers around a cigarette bin that was theorized to be inhabited by micro-organisms capable
of efficiently degrading cigarette filters. The bacterial community within the cigarette bin was
previously investigated using 16S small subunit rRNA metagenomic sequencing, as well as a
metagenomic library. The aim of this project was to investigate the cigarette bin for cultivatable
fungal isolates and select an isolate for in vitro enzyme analysis using para-nitrophenyl-linked
substrates that mirrors the catabolic pathway of cellulose acetate. Four fungal isolates were
cultivated from the cigarette bin and designated I1, I2, I3, and I4. Phylogenetic inference for
the four isolates identified as Mucor circinelloides f. circinelloides (I1, I2, and I3) and
Fusarium proliferatum (I4). The four isolates were screened via multiple functional plate-based
screening recipes for the selection of a candidate isolate for in vitro enzyme analysis. The
candidate isolate selected was Fusarium proliferatum due to the successful screening and
observed genetic adaptability towards carboxymethyl cellulose. The in vitro enzyme analysis
of Fusarium proliferatum indicated a β-glucosidase activity of 115.7 nkat/mg of protein
towards 4–nitrophenyl–β–D–glucopyranoside and acetyl esterase activity of 157.9 nkat/mg of
protein towards 4–nitrophenyl acetate. These preliminary results infer the potential
applications of Fusarium proliferatum for the remediation of cigarette filter pollution.
Valorization of cigarette filters within a fungal-based biorefinery using Fusarium proliferatum
could generate bioethanol and other high-value products.
Description
Thesis (MScAgric)--Stellenbosch University, 2020.
Keywords
Cigarette filters -- Pollution, Greenhouse gases, Filters and filtration -- Environmental aspects, Cellulose acetate, Enzymes -- Analysis, Greenhouse effect, Atmospheric, UCTD