How Mushrooms Use Plant Fibers for Growth

Greg Howard
22nd April, 2024

Image Source: Natural Science News, 2024

Key Findings

Researchers at Wageningen University found that the common mushroom can fully utilize lignin, not just degrade it
The mushroom converts lignin into its own biomass, challenging previous beliefs about fungi's role in carbon cycling
This discovery could impact our understanding of soil carbon storage and climate change predictions

Understanding the role of fungi in the carbon cycle is crucial, particularly as we face climatic challenges that demand a deeper knowledge of carbon storage and release in ecosystems. Soil, a significant carbon sink, harbors complex interactions between microorganisms and organic matter that influence carbon storage^[2]. A recent study by researchers at Wageningen University & Research^[1] has shed new light on the capabilities of fungi, particularly Agaricus bisporus, the common mushroom, in processing plant biomass, specifically lignin, a component previously thought to be only partially utilized by fungi. Lignin, an organic polymer found in plant cell walls, provides plants with rigidity and resistance to degradation. It is known to be a tough molecule for microorganisms to break down and utilize^[3]. The conventional view has been that fungi, particularly saprotrophic fungi which feed on dead or decaying organic matter, primarily metabolize carbohydrates from plant biomass, breaking down lignin only to a limited extent without fully utilizing it for growth. This understanding has implications for industries such as paper production and biofuel generation, where lignin removal and processing are critical steps^[3]. The study by Wageningen University & Research challenges this view by demonstrating that Agaricus bisporus can do more than just degrade lignin; it can also metabolize it, incorporating lignin into its own biomass. To prove this, the researchers used a form of lignin labeled with 13C, a non-radioactive form of carbon that can be tracked through metabolic processes. They observed that the fungus not only broke down the lignin but also used it to build fungal structures, converting it into proteinogenic amino acids, the building blocks of proteins. The concept of carbon use efficiency (CUE), which is the efficiency with which organisms convert absorbed organic carbon into their own biomass, was central to this study. Previous research has highlighted the importance of microbial CUE in determining soil organic carbon (SOC) storage and its variation across the globe^[2]. The researchers found that Agaricus bisporus had a lignin CUE of 0.14 (g/g), meaning that for every gram of lignin carbon consumed, 0.14 grams were converted into fungal biomass. This demonstrates that lignin is not only a structural challenge to be overcome but also a potential source of carbon for growth. The implications of this discovery are significant for our understanding of carbon cycling. If fungi can metabolize lignin more extensively than previously thought, this could change how we view their role in the carbon cycle. Fungi might be more influential in carbon sequestration and release than we realized, which could affect predictions of SOC feedback in response to climate change^[2]. Furthermore, the methods used by fungi to deconstruct lignocellulose are diverse and involve various enzymes^[4]. The study's findings suggest that the fungal metabolic pathways that convert lignin into cellular building blocks are complex and potentially involve aromatic ring-cleaved intermediates. This aligns with previous research showing that a range of organisms, including bacteria and white-rot fungi, possess mechanisms to break down lignocellulose^[4]^[5]. The Wageningen University & Research study adds to this body of knowledge by highlighting the metabolic value of lignin for fungi, suggesting that fungi can utilize lignin in ways similar to other components of plant biomass. In conclusion, the research from Wageningen University & Research not only challenges the existing paradigm that fungi primarily metabolize carbohydrates but also positions lignin as a valuable carbon source for fungal growth. This breakthrough could have far-reaching implications for our understanding of terrestrial carbon dynamics and the potential biotechnological applications of fungi in biomass conversion and the development of sustainable production processes.

Biochem Plant Science Mycology