Microbial plant bioprocessing - what can we learn from the cow?

Date:
September 20, 2021
Source:
Stellenbosch University
Summary:
The most significant sources of organic waste in South Africa is
sugarcane bagasse (5.35 million metric tonnes), invasive plants
(11.30 million metric tonnes) and fruit wastes (1.3 billion
metric tonnes).

Microbiologists from Stellenbosch University are investigation
the use of mammalian rumen in the anaerobic digestive process to
break down or separate organic waste into its original building
blocks, from where it can subsequently be converted into various
high-value products -- just as a cow does with processing the
tough plant material into the basic building blocks upon which
the production of milk is based.



FULL STORY ==========================================================================
For billions of years, Nature has perfected ways of dealing with the
recycling of materials. Like a good housekeeper who saves as much as
she can, she knows how to avoid what is too much and too little.


==========================================================================
One of the best examples of this thrifty behaviour of Nature is the
evolution of ruminants: animals such as deer, goats, cows and antelope
have developed a unique digestive system, consisting of four different stomachs, to convert even the toughest grasses and leaves into nourishing
milk, wool and protein.

Remember, as a child, how one cringed at the idea of regurgitating your
own food to chew on it before it being swallowed again? Well, cows spend
about eight hours of their day doing exactly that, thereby assisting
their microbial community to process the raw plant food.

A cow is therefore a natural example of consolidated bioprocessing where cellulose (in plantmaterial) is hydrolysed and converted to various
products in a single vessel (the cow). So what can we learn from Nature,
and more specifically cows, when dealing with the 83 million metric tons
of agricultural, municipal and fruit waste produced in South Africa
every year? According to microbiologists at Stellenbosch University,
the concept of a biorefinery based on the four-stomach digestive system
of ruminants, may just be key to the establishment of simple and robust, small-scale biorefinery operations in South Africa and Africa.

Prof Emile van Zyl, distinguished professor in microbiology at SU,
says first- world countries have made significant progress over the
last few decades in the development of capital-intensive and advanced technologies to produce bioethanol from plant material. Yet, as long
as relatively cheap fossil fuels are around, the upscaling of these technologies remain commercially non-viable.

"South Africa and Africa cannot afford the huge capital costs of
large-scale cellulosic ethanol plants and the technological challenges associated with it," he explains.

That is why, in a recent review published in the journal Catalysis,
they propose the introduction of the rumen microbiome into anaerobic
digestion processes. Currently, mixed anaerobic microbial cultures are
used to break down organic matter to generate mostly biogas, and much
research is aimed at finding the most efficient microbes and identifying
the parameters for their optimal functioning. Yet, argue the researchers, mammalian ruminants have naturally evolved to perform anaerobic digestion
of plant material.

Furthermore, instead of producing biogas, they suggest supressing that
latter part of the digestion process and rather use microbial hosts to
produce industrial important organic acids, such as acetic, propionic,
butyric and valeric and caproic acids from agricultural wastes. Yeast biotechnology can also be employed for the conversion of malic acid
in grape and apple pomace to higher-value lactic, citric, fumaric and
succinic acids. For example, the current value of organic acids can vary
from about US$600 per metric ton for acetic acid to more than US$2000
per metric ton for carbon 4-6 carboxylic acids. With the rise in demand
for bioplastics, organic polymers such as polylactate reach values of
more than US$3500 per metric ton.

Prof Marinda Viljoen-Bloom, one of the co-authors, says while the
application of rumen microbes for the digestion of plant material is
not a new concept, it remains a challenge to replicate the complicated interactions found in ruminants in a bioreactor. In the Biofuels Research
Group at the Department of Microbiology, they are specifically looking at
ways to add value to South African waste streams: For his PhD, Dr Sesethu Njokweni explored the anaerobic production of volatile fatty acids from agricultural waste, while PhD student Annica Steyn is constructing a recombinant yeast strain that can effectively convert malic acid to higher-value organic acids.

Did you know? The most significant sources of organic waste in South
Africa is sugarcane bagasse (5.35 million metric tonnes), invasive plants (11.30 million metric tonnes) and fruit wastes (1.3 billion metric
tonnes). Microbiologists from Stellenbosch University are investigation
the use of mammalian rumen in the anaerobic digestive process to break
down or separate organic waste into its original building blocks, from
where it can subsequently be converted into various high-value products
-- just as a cow does with processing the tough plant material into the
basic building blocks upon which the production of milk is based.

========================================================================== Story Source: Materials provided by Stellenbosch_University. Original
written by Wiida Fourie-Basson. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Sesethu Gift Njokweni, Annica Steyn, Marelize Botes, Marinda
Viljoen-
Bloom, Willem Heber van Zyl. Potential Valorization of Organic Waste
Streams to Valuable Organic Acids through Microbial Conversion:
A South African Case Study. Catalysts, 2021; 11 (8): 964 DOI:
10.3390/ catal11080964 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210920121738.htm

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