last for several years in in vitro transfers (Bauchop and Mountfort 1981; Li et al. 2016).
Microbial consortia dominated by species
of Clostridia in syntrophic relationship with
methanogenic archaea are relatively ineffective
at degrading recalcitrant lignocellulosic substrates (Bauchop and Mountfort 1981; Irvine
and Stewart 1991; Joblin et al. 1989). In contrast, stable co-cultures of anaerobic fungi and
methanogens may offer faster rates of biogas
production and reduced hydraulic retention
times; both significant advantages for commercial biogas production. However, our understanding of the role and survival of anaerobic
fungi in conventional biogas processes is limited, and scale-up techniques have not yet been
realized. Nonetheless, fungus-methanogen coculture offers the possibility of consolidated
bioprocessing, using a single platform for the
complete deconstruction of lignocellulose and
its conversion to biogas. Hence this area of
research is likely to receive increasing attention
in the future.
IV. Current and Future Opportunities
for Exploitation
Beyond basic science research, the anaerobic
fungi have been attracting attention for their
translational potential to a wealth of industries
from bio-based processing to animal health and
welfare and beyond. Novel technologies based
on engineered anaerobic fungal strains and/or
processing strategies have seen a number of
intellectual property filings worldwide, as discussed below. We further provide a brief overview for exploitation of unknown secondary
metabolites and membrane proteins sourced
from anaerobic fungi, which are useful to biobased chemical production and strain engineering.
A. Potential Source of Commodity via
Secondary Metabolites
Anaerobic fungi perform mixed acid fermentation for energy generation and thus produce
formate, acetate, lactate, ethanol, CO 2 , and
hydrogen during the conversion of plant biomass (Mountfort and Orpin 1994). They are
able to effectively degrade lignocellulosic biomass (Seppa ¨la ¨ et al. 2017) and thus could help
to exploit such abundant and cheap substrates
for organic acid production. Several studies
indicate the potential of anaerobic fungi to produce organic acids (Dollhofer et al. 2018;
Nkemka et al. 2015), but the yield, the concentration, and the productivity need to be determined to decide if their utilization could be an
economical approach to produce platform
chemicals (Sauer et al. 2008). Furthermore,
anaerobic fungi survive in a highly complex
ecosystem alongside numerous bacteria,
methanogenic archaea, and protozoa. To thrive
in this competitive environment, it is likely
that they produce secondary metabolites to
boost their chances for survival. Progress in
integrated-omics (Hillman et al. 2017) combined with the screening of a diverse set of
anaerobic fungal isolates could thus potentially
deliver a plethora of novel natural products for
biotechnological use.
B. Characterization and Metabolic Engineering
with Membrane Proteins
Current biotechnology uses easily engineered
microorganisms, such as Saccharomyces cerevisiae, to convert lignocellulosic biomass into a
wide range of fuels and chemicals. A major
limitation is the poor ability of yeast to efficiently co-utilize glucose and xylose, the second
most abundant sugar in plant biomass (Yang
et al. 2007). As discussed in Sect. II.B, exogenous enzymes and pathways have been engineered into yeast that permit the conversion of
xylose into ethanol, but poor xylose uptake into
the cells remains a severe bottleneck (Young
et al. 2011). Therefore, membrane proteins
such as transporters for underutilized sugars
that can be used to bolster transport in yeast
are highly sought after (recently reviewed in
Hara et al. (2017)). Primary sequence analyses
of a dataset comprising >60,000 transcripts
sourced from three strains of anaerobic
fungi suggest that besides biomass-degrading
17 The Biotechnological Potential of Anaerobic Gut Fungi
427
Microbial consortia dominated by species
of Clostridia in syntrophic relationship with
methanogenic archaea are relatively ineffective
at degrading recalcitrant lignocellulosic substrates (Bauchop and Mountfort 1981; Irvine
and Stewart 1991; Joblin et al. 1989). In contrast, stable co-cultures of anaerobic fungi and
methanogens may offer faster rates of biogas
production and reduced hydraulic retention
times; both significant advantages for commercial biogas production. However, our understanding of the role and survival of anaerobic
fungi in conventional biogas processes is limited, and scale-up techniques have not yet been
realized. Nonetheless, fungus-methanogen coculture offers the possibility of consolidated
bioprocessing, using a single platform for the
complete deconstruction of lignocellulose and
its conversion to biogas. Hence this area of
research is likely to receive increasing attention
in the future.
IV. Current and Future Opportunities
for Exploitation
Beyond basic science research, the anaerobic
fungi have been attracting attention for their
translational potential to a wealth of industries
from bio-based processing to animal health and
welfare and beyond. Novel technologies based
on engineered anaerobic fungal strains and/or
processing strategies have seen a number of
intellectual property filings worldwide, as discussed below. We further provide a brief overview for exploitation of unknown secondary
metabolites and membrane proteins sourced
from anaerobic fungi, which are useful to biobased chemical production and strain engineering.
A. Potential Source of Commodity via
Secondary Metabolites
Anaerobic fungi perform mixed acid fermentation for energy generation and thus produce
formate, acetate, lactate, ethanol, CO 2 , and
hydrogen during the conversion of plant biomass (Mountfort and Orpin 1994). They are
able to effectively degrade lignocellulosic biomass (Seppa ¨la ¨ et al. 2017) and thus could help
to exploit such abundant and cheap substrates
for organic acid production. Several studies
indicate the potential of anaerobic fungi to produce organic acids (Dollhofer et al. 2018;
Nkemka et al. 2015), but the yield, the concentration, and the productivity need to be determined to decide if their utilization could be an
economical approach to produce platform
chemicals (Sauer et al. 2008). Furthermore,
anaerobic fungi survive in a highly complex
ecosystem alongside numerous bacteria,
methanogenic archaea, and protozoa. To thrive
in this competitive environment, it is likely
that they produce secondary metabolites to
boost their chances for survival. Progress in
integrated-omics (Hillman et al. 2017) combined with the screening of a diverse set of
anaerobic fungal isolates could thus potentially
deliver a plethora of novel natural products for
biotechnological use.
B. Characterization and Metabolic Engineering
with Membrane Proteins
Current biotechnology uses easily engineered
microorganisms, such as Saccharomyces cerevisiae, to convert lignocellulosic biomass into a
wide range of fuels and chemicals. A major
limitation is the poor ability of yeast to efficiently co-utilize glucose and xylose, the second
most abundant sugar in plant biomass (Yang
et al. 2007). As discussed in Sect. II.B, exogenous enzymes and pathways have been engineered into yeast that permit the conversion of
xylose into ethanol, but poor xylose uptake into
the cells remains a severe bottleneck (Young
et al. 2011). Therefore, membrane proteins
such as transporters for underutilized sugars
that can be used to bolster transport in yeast
are highly sought after (recently reviewed in
Hara et al. (2017)). Primary sequence analyses
of a dataset comprising >60,000 transcripts
sourced from three strains of anaerobic
fungi suggest that besides biomass-degrading
17 The Biotechnological Potential of Anaerobic Gut Fungi
427