• Microbial plant bioprocessing - what can

    From ScienceDaily@1:317/3 to All on Mon Sep 20 21:30:46 2021
    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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