About this Research Topic
Anaerobic fungi and ciliate protozoa represent up to half of the herbivore gut microbial biomass. They are generally recognized as mutualistic symbionts in ruminant animals since they produce a wide range of cellulolytic and amylolytic enzymes and play a key role in feed degradation for the host. This is particularly true of anaerobic fungi, which have the most potent fiber degrading enzymes in the known biological world. The presence of these microbial eukaryotes enables ruminants to digest large amounts of highly fibrous substrates. Their initial physical and enzymatic attack on plant fiber results in the breakdown of highly complex carbohydrates, releasing polymers and monomers that can be used by the remainder of the microbial community and potentially the host itself. Due to the production of hydrogen in their hydrogenosomes, anaerobic fungi and especially the motile ciliate protozoa provide comfortable micro-habitats for hydrogen-scavenging bacteria and methanogenic archaea.
The herbivore gut microbiome also contains dense and diverse populations of viruses. The majority of these viruses are not transient, instead, they actively infect and replicate within the microbes of the gut (for example, bacteriophages and archaeal viruses). These viruses cause microbial lysis and contribute to microbial gene transfer, with prophages often found within gut microbial genomes.
Despite the clear importance of these three taxa to our understanding of herbivore gut function and microbial ecology, only bacteria and archaea are commonly characterized in herbivore gut studies. There is an urgent need to adopt more holistic approaches to the study of the herbivore gut microbiome. Only then can the complex interactions within the herbivore gut microbiome be better understood, facilitating the development of novel and sustainable approaches to benefit the nutrition and health of the host whilst improving the host's ecological impact and environmental footprint.
This research topic, therefore, focusses on advances in understanding the roles of commensal anaerobic fungi, ciliate protozoa, and viruses in the herbivore gut, as well as the challenges and opportunities associated with the study of them. The scope of this topic includes both mammalian and non-mammalian herbivores and is open to all types of research (e.g. pure/axenic culture, mixed culture, in vitro, microcosm, in vivo, environmental and in silico). Both applied and fundamental studies are welcomed, including the biotechnological application of these taxa and/or materials (e.g. enzymes) derived from them. All publication types are welcomed, including research articles, reviews, and opinion papers.
This research topic is also a tribute to the tremendous contributions of Professor Colin Orpin and the late Professor Burk Dehority to the field of herbivore gut microbiology. The ground-breaking work of Colin Orpin in the early 1970's was a paradigm shift in our understanding of fungal biology, as until his work all fungi were believed to respire aerobically. Between 1957 and 2013, Burk Dehority pioneered research into synergism of prokaryotic and eukaryotic microbial species for the digestion of plant fiber. He shed light onto the vast diversity and beauty of ciliate protozoa in both domesticated and non-domesticated herbivorous animals and described no less than 21 new species.
Keywords: Rumen, Anaerobic Fungi, Protozoa, Phages, Herbivory
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