Hydrogenosome, Pairing Anaerobic Fungi and H2-Utilizing Microorganisms Based on Metabolic Ties to Facilitate Biomass Utilization

Abstract

Anaerobic fungi, though low in abundance in rumen, play an important role in the degradation of forage for herbivores. When only anaerobic fungi exist in the fermentation system, the continuous accumulation of metabolites (e.g., hydrogen (H2) and formate) generated from their special metabolic organelles—the hydrogenosome—inhibits the enzymatic reactions in the hydrogenosome and reduces the activity of the anaerobic fungi. However, due to interspecific H2 transfer, H2 produced by the hydrogenosome can be used by other microorganisms to form valued bioproducts. This symbiotic interaction between anaerobic fungi and other microorganisms can be used to improve the nutritional value of animal feeds and produce value-added products that are normally in low concentrations in the fermentation system. Because of the important role in the generation and further utilization of H2, the study of the hydrogensome is increasingly becoming an important part of the development of anaerobic fungi as model organisms that can effectively improve the utilization value of roughage. Here, we summarize and discuss the classification and the process of biomass degradation of anaerobic fungi and the metabolism and function of anaerobic fungal hydrogensome, with a focus on the potential role of the hydrogensome in the efficient utilization of biomass.

Molecular identification of anaerobic fungi isolated from buffalo rumen with their growth rate, cellulase enzyme activity, and fermentation products characteristics

“…At high concentrations, one of the substances toxic to fungi in the medium is hydrogen. This was in accordance with Saye et al (2021) and Ma et al (2022), who reported that the accumulation of hydrogen could inhibit the metabolism of rumen anaerobic fungi, while Li et al (2021) also discovered that it hinders the performance of the hydrogenase enzyme. Hydrogenase is one of the important enzymes in the fungal hydrogenosome, which plays a role in the metabolism of carbohydrates to form energy (ATP) for fungi (Leger et al 2013;Ma et al 2022).…”

“…Moreover, another substance that can inhibit the growth of fungi was the accumulation of formic acid (Ma et al 2022). According to Joblin and Naylor (1993), formic acid is a strong inhibitor for the growth of anaerobic fungi, which is produced through the fermentation process by anaerobic fungi together with acetate, lactate, ethanol, and CO2 (Cheng et al 2013;Hess et al 2020;Panahi et al 2022).…”

“…Li et al (2017) also stated that the energy source is brought into the cell before being used, and the cellobiose will be carried into fungal cells via the cellodextrin transporter (CDT) and converted into glucose by the β-glucosidase. The glucose in fungal cells will pass through the glycolysis stage to produce ATP and other fermentation products (Boxma et al 2004) when it is introduced into the cytoplasm by glucose transporters (Ma et al 2022).…”

“…They can produce enzymes to degrade fibers such as cellulase, hemicellulase, as well as xylanase (Ho et al 1996), and also penetrate feed particles using rhizoids (Ho and Barr 1995;Kittelmann et al 2012;Solomon et al 2016). Anaerobic fungi can produce xylanase, mannanase, galactanase, exoglucanase, endoglucanase and βglucosidase wich plays an important role for feed fiber degradation (Chen et al 2012;Youssef et al 2013;Wang et al 2014;Ma et al 2022). These fungi also produce lignocellulase enzymes to degrade feed cell walls and generate acetate, formate, lactate, ethanol, H2, and CO2 as fermentation products (Gruninger et al 2014).…”

Anaerobic Fungi Isolated From Bactrian Camel Rumen Contents Have Strong Lignocellulosic Bioconversion Potential

“…Anaerobic fungi in the rumen are exposed to higher concentrations of methane than anaerobic fungi in feces, which also explains higher hydrogen production by isolates from rumen contents. The rumen environment promotes the production of metabolites of hydrogenosome in anaerobic fungi, and this feature is preserved even in the anaerobic fungi isolated from the in vitro rumen fermentation system ( Ma et al, 2022 ). In our study, although fungi from different sources share the same fermentation conditions (temperature and substrate types) in the in vitro system, strains isolated from rumen contents had higher hydrogen production than those from feces.…”