may not possess anaerobic fungi such as swine
and poultry (Gruninger et al. 2014). To use the
treated substrate, pressing, drying, and sterilization procedures would be necessary. Palatability and energy/cost studies would be
needed to determine if such an approach is
practically feasible.
The application of anaerobic fungi as probiotics for ruminants has been studied in buffalo (Paul et al. 2004; Saxena et al. 2010), buffalo
calves (Paul et al. 2011; Tripathi et al. 2007), and
Holstein-Friesian calves (Dey et al. 2004). In the
latter study, the control group was not fed with
fungus-free medium or inactivated fungal culture; thus the results of this study are inconclusive. In all other studies, adequate control diets
were applied. Diets directly supplemented with
anaerobic fungal cultures improved the rumen
fermentation characteristics (pH, volatile fatty
acids, and nitrogen content) and enhanced the
ruminal microbial population and CAZyme
activities. As a consequence, increased animal
growth rate, digestibility of nutrients, and
nitrogen retention was observed. In lactating
buffalos, administration of anaerobic fungi
also increased milk fat by up to 6% (Saxena
et al. 2010).
The effect of administration of anaerobic
fungal cultures (Orpinomyces sp.) and enzymes
on ruminal digestion was studied also in sheep
(Lee et al. 2000). Fungal enzymes (hydrolases
produced by Orpinomyces sp.) did not influence fermentation parameters. In contrast, a
significant positive response was obtained
with administration of a live fungal culture.
Collectively, these studies indicate that anaerobic fungi can be used as a probiotic to enhance
diet digestibility leading to higher production.
Nevertheless, this approach must take account
of economic considerations and the need to
repeatedly administrate oral-dosages of anaerobic fungi to maintain the desired response
(Ribeiro et al. 2017).
B. Bioethanol Production with Anaerobic
Fungi
Bioethanol production has increased dramatically over the last two decades (Balat and Balat
2009), and there is a critical need to transition
from “first-generation” bioethanol derived
from sugar cane and maize to “second-generation” fuels derived from lignocellulosic residues (Mood et al. 2013). The bioethanol
process consists of four stages: pretreatment,
enzymatic hydrolysis, fermentation, and distillation (Aditiya et al. 2016). Most bioethanol is
commercially produced by fermentations
involving adapted or genetically modified
strains of Saccharomyces cerevisiae, Zymomonas mobilis, and Escherichia coli (Yang et al.
2007) that cannot natively degrade lignocellulose. The limiting factor in the production of
bioethanol from second generation crops is the
initial release of fermentable sugars from the
recalcitrant lignocellulosic biomass (Dashtban
et al. 2009). This is commonly overcome by the
application of costly mechanical and/or chemical pretreatments such as milling, alkaline or
acid hydrolysis, ionic liquid pretreatment or
steam explosion (Sharma et al. 2017). The
unique ability of anaerobic fungi to infiltrate
and enzymatically degrade untreated lignocellulosic substrates makes them attractive candidates for alternative microbial conversion of
plant biomass prior to bioethanol production.
For example, Anaeromyces robustus and Neocallimastix californiae have been employed in a
batch fermentation to drive growth of Saccharomyces cerevisiae by the release of sugars generated by fungal hydrolysis of lignocellulose
(Henske et al. 2018b). Additionally, Pecoramyces ruminantium has been used in a
saccharification-fermentation approach for
hydrolysis of different alkaline pretreated lignocellulosic substrates prior to ethanol production by Escherichia coli (Ranganathan et al.
2017). Yields of ethanol were (approximately
one third) lower than that achieved after using
commercial enzyme cocktails but the authors
conclude that their approach is potentially
more cost-effective than enzyme technology,
and yields are potentially optimizable through
the use of selected/modified strains and
enhanced process design (Ranganathan et al.
2017).
Another limitation to the production of
bioethanol from lignocellulosic biomass is the
inability of many ethanol-producing yeasts to
424
V. Flad et al.
and poultry (Gruninger et al. 2014). To use the
treated substrate, pressing, drying, and sterilization procedures would be necessary. Palatability and energy/cost studies would be
needed to determine if such an approach is
practically feasible.
The application of anaerobic fungi as probiotics for ruminants has been studied in buffalo (Paul et al. 2004; Saxena et al. 2010), buffalo
calves (Paul et al. 2011; Tripathi et al. 2007), and
Holstein-Friesian calves (Dey et al. 2004). In the
latter study, the control group was not fed with
fungus-free medium or inactivated fungal culture; thus the results of this study are inconclusive. In all other studies, adequate control diets
were applied. Diets directly supplemented with
anaerobic fungal cultures improved the rumen
fermentation characteristics (pH, volatile fatty
acids, and nitrogen content) and enhanced the
ruminal microbial population and CAZyme
activities. As a consequence, increased animal
growth rate, digestibility of nutrients, and
nitrogen retention was observed. In lactating
buffalos, administration of anaerobic fungi
also increased milk fat by up to 6% (Saxena
et al. 2010).
The effect of administration of anaerobic
fungal cultures (Orpinomyces sp.) and enzymes
on ruminal digestion was studied also in sheep
(Lee et al. 2000). Fungal enzymes (hydrolases
produced by Orpinomyces sp.) did not influence fermentation parameters. In contrast, a
significant positive response was obtained
with administration of a live fungal culture.
Collectively, these studies indicate that anaerobic fungi can be used as a probiotic to enhance
diet digestibility leading to higher production.
Nevertheless, this approach must take account
of economic considerations and the need to
repeatedly administrate oral-dosages of anaerobic fungi to maintain the desired response
(Ribeiro et al. 2017).
B. Bioethanol Production with Anaerobic
Fungi
Bioethanol production has increased dramatically over the last two decades (Balat and Balat
2009), and there is a critical need to transition
from “first-generation” bioethanol derived
from sugar cane and maize to “second-generation” fuels derived from lignocellulosic residues (Mood et al. 2013). The bioethanol
process consists of four stages: pretreatment,
enzymatic hydrolysis, fermentation, and distillation (Aditiya et al. 2016). Most bioethanol is
commercially produced by fermentations
involving adapted or genetically modified
strains of Saccharomyces cerevisiae, Zymomonas mobilis, and Escherichia coli (Yang et al.
2007) that cannot natively degrade lignocellulose. The limiting factor in the production of
bioethanol from second generation crops is the
initial release of fermentable sugars from the
recalcitrant lignocellulosic biomass (Dashtban
et al. 2009). This is commonly overcome by the
application of costly mechanical and/or chemical pretreatments such as milling, alkaline or
acid hydrolysis, ionic liquid pretreatment or
steam explosion (Sharma et al. 2017). The
unique ability of anaerobic fungi to infiltrate
and enzymatically degrade untreated lignocellulosic substrates makes them attractive candidates for alternative microbial conversion of
plant biomass prior to bioethanol production.
For example, Anaeromyces robustus and Neocallimastix californiae have been employed in a
batch fermentation to drive growth of Saccharomyces cerevisiae by the release of sugars generated by fungal hydrolysis of lignocellulose
(Henske et al. 2018b). Additionally, Pecoramyces ruminantium has been used in a
saccharification-fermentation approach for
hydrolysis of different alkaline pretreated lignocellulosic substrates prior to ethanol production by Escherichia coli (Ranganathan et al.
2017). Yields of ethanol were (approximately
one third) lower than that achieved after using
commercial enzyme cocktails but the authors
conclude that their approach is potentially
more cost-effective than enzyme technology,
and yields are potentially optimizable through
the use of selected/modified strains and
enhanced process design (Ranganathan et al.
2017).
Another limitation to the production of
bioethanol from lignocellulosic biomass is the
inability of many ethanol-producing yeasts to
424
V. Flad et al.