Anaerobic Fungi: Past, Present, and Future

Abstract

Anaerobic fungi (AF) play an essential role in feed conversion due to their potent fiber degrading enzymes and invasive growth. Much has been learned about this unusual fungal phylum since the paradigm shifting work of Colin Orpin in the 1970s, when he characterized the first AF. Molecular approaches targeting specific phylogenetic marker genes have facilitated taxonomic classification of AF, which had been previously been complicated by the complex life cycles and associated morphologies. Although we now have a much better understanding of their diversity, it is believed that there are still numerous genera of AF that remain to be described in gut ecosystems. Recent markergene based studies have shown that fungal diversity in the herbivore gut is much like the bacterial population, driven by host phylogeny, host genetics and diet. Since AF are major contributors to the degradation of plant material ingested by the host animal, it is understandable that there has been great interest in exploring the enzymatic repertoire of these microorganisms in order to establish a better understanding of how AF, and their enzymes, can be used to improve host health and performance, while simultaneously reducing the ecological footprint of the livestock industry. A detailed understanding of AF and their interaction with other gut microbes as well as the host animal is essential, especially when production of affordable high-quality protein and other animal-based products needs to meet the demands of an increasing human population. Such a mechanistic understanding, leading to more sustainable livestock practices, will be possible with recently developed-omics technologies that have already provided first insights into the different contributions of the fungal and bacterial population in the rumen during plant cell wall hydrolysis.

Early life dietary intervention in dairy calves results in a long-term reduction in methane emissions

“…As protozoa, rumen fungi are also involved in interspecies H 2 transfer with methanogens 64 . They also produce formate, another common substrate for methane synthesis, and might have a role in overall enteric methane emissions 65 . Similarly to bacteria and archaea, the fungal community structure differed between CONT and 3-NOP calves but no divergence in their abundance was detected.…”

Interactions between Anaerobic Fungi and Methanogens in the Rumen and Their Biotechnological Potential in Biogas Production from Lignocellulosic Materials

“…In 2007, anaerobic fungi were classified as an independent phylum called Neocallimastigomycota [ 23 ]. To date, the following eighteen genera of anaerobic fungi have been identified ( Table 1 ) according to their growth type, rhizoidal morphology, and number of zoospore flagellum [ 24 ]: Neocallimastix, Caecomyces, Orpinomyces, Piromyces, Anaeromyces, Cyllamyces, Buwchfawromyces, Oontomyces, Pecoramyces, Feramyces, Liebetanzomyces, Agriosomyces, Aklioshbomyces, Capellomyces, Ghazallomyces, Joblinomyces, Khoyollomyces, and Tahromyces. As shown in Table 1 , it has been nearly four decades since the first anaerobic fungi were identified and since then, most anaerobic fungi have been isolated from ruminant feces.…”

The Present Role and New Potentials of Anaerobic Fungi in Ruminant Nutrition

“…Whilst also the domains archaea and protozoa gained attention in terms of methane emissions or intra-ruminal nitrogen (N) recycling [ 2 , 3 ], AF (phylum Neocallimastigomycota) have yet been widely neglected in the wider ruminant nutrition research. However, these obligate anaerobes are commensals along the gastrointestinal tract of ruminants, being mainly present in the forestomach [ 4 ], and truly vital for sufficient fiber degradation by means of expressing various carbohydrate-active enzymes (CAZymes), which can be organized in cellulosomes, as well as physically penetrating plant material via rhizoidal systems [ 5 , 6 , 7 ].…”

“…In fact, AF and their capabilities are highly recognized among microbiologists and comprehensive scientific efforts have been made regarding their taxonomy, lifecycle, and metabolic characterization, which recently was excellently summarized by Hess et al [ 5 ]. Notwithstanding, AF appear to be equally relevant to ruminant nutritionists, who continually seek for strategies to optimize ruminal fiber degradation, a process in which AF are indeed substantially involved [ 5 , 7 ]. Likewise, this microbial clade seems significant for further aspects related to modern livestock feeding.…”

“…Therefore, by portraying the current perception of AF in ruminant nutrition and outlining their potential in this research field, this review extends the perspective on AF and aims to stimulate scientific discourse on their relevance in modern ruminant feeding as well as sensitize ruminant scientists for these hidden champions in the gut. Since Hess et al [ 5 ] provide an extensive status quo on AF live cycle and taxonomy, the present review will not cover those aspects, albeit a new fungal taxon has again been isolated in the meantime [ 8 ]. Similarly, the reader is further encouraged to consult the article of Vinzelj et al [ 9 ] for general basics on AF as well as thorough considerations about their cultivation.…”