Abstract
Homo-acetogens are microbes that have the ability to grow on gaseous substrates such as H2/CO2/CO and produce acetic acid as the main product of their metabolism through a metabolic process called reductive acetogenesis. These acetogens are dispersed in nature and are found to grow in various biotopes on land, water and sediments. They are also commonly found in the gastro-intestinal track of herbivores that rely on a symbiotic relationship with microbes in order to breakdown lignocellulosic biomass to provide the animal with nutrients and energy. For this motive, the fermentation scheme that occurs in the rumen has been described equivalent to a consolidated bioprocessing fermentation for the production of bioproducts derived from livestock. This paper reviews current knowledge of homo-acetogenesis and its potential to improve efficiency in the rumen for production of bioproducts by replacing methanogens, the principal H2-scavengers in the rumen, thus serving as a form of carbon sink by deviating the formation of methane into bioproducts. In this review, we discuss the main strategies employed by the livestock industry to achieve methanogenesis inhibition, and also explore homo-acetogenic microorganisms and evaluate the members for potential traits and characteristics that may favor competitive advantage over methanogenesis, making them prospective candidates for competing with methanogens in ruminant animals.
Highlights
Introduction to HomoAcetogensHomo-acetogens are bacteria known for being capable to have a versatile metabolism for diverse substrate consumption, including the ability to grow on gaseous substrates using the acetyl-CoA pathway for fixing carbon dioxide (CO2 ) using hydrogen (H2 ) for synthesizing acetyl-CoA
We have investigated various homo-acetogens found in different habitats to study their growth characteristics and competitive relationship with hydrogenotrophic methanogens
We examined different environments for potential bioprospection of homo-acetogens
Summary
Homo-acetogens are bacteria known for being capable to have a versatile metabolism for diverse substrate consumption, including the ability to grow on gaseous substrates using the acetyl-CoA pathway for fixing carbon dioxide (CO2 ) using hydrogen (H2 ) for synthesizing acetyl-CoA. It is this pathway that defines an homo-acetogen and is called the Wood–Ljungdahl (WD) pathway, which has been studied over the years, especially for the direct fixation of CO2 by the acetyl-CoA synthase enzyme to produce acetate as the energy molecule [1]. The hexagons numbered from 1–7 represent enzymes involved in the fixation of H2 -CO2 in WL pathway; 1—formyl dehydrogenase, 2—formyl tetrahydrofolate synthase, 3—formyl tetrahydrofolate cyclohydrolase, 4—methylene tetrahydrofolate dehydrogenase, 5—ethylene tetrahydrofolate reductase, 6—methyl transferase, 7—carbon monoxide dehydrogenase/acetyl-CoA synthase
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