Jul 2026· Proceedings of the Nutrition Society· pp.
1-29
· 0 citations
Medicine
TL;DR
Investigation into gut microbial communities conducted by Harry Flint and his research group found extracellular cellulosome and amylosome enzyme complexes were found to mediate the breakdown of plant cell walls and resistant starch by specialised Firmicutes bacteria, both in the human colon and in the rumen.
Abstract
Gut micro-organisms possess biochemical capabilities that far exceed those of their mammalian hosts, particularly in the ability to gain energy from the breakdown of diet-derived plant material (fibre). This article reviews investigations into gut microbial communities conducted by Harry Flint and his research group. First, extracellular cellulosome and amylosome enzyme complexes were found to mediate the breakdown of plant cell walls and resistant starch by specialised Firmicutes bacteria, both in the human colon and in the rumen. In contrast, Bacteroidetes (Bacteroides, Prevotella spp.) rely on their ability to capture soluble carbohydrates. Human dietary studies examining the impact of fibre sources upon microbiota composition and metabolism identified 'diet-responsive' species. In addition, dominant species of butyrate-producing bacteria, including a subset able to convert lactate to butyrate, were isolated from healthy human volunteers. Most produce butyrate from carbohydrates via butyryl-CoA:acetate CoA-transferase, with uptake of external acetate, while lactate conversion is associated with a highly inducible gene cluster (lct). In pH-controlled chemostat studies, mildly acid pH depressed growth of propionate-producing Bacteroidetes, but favoured butyrate production by Firmicutes. This may explain why % butyrate among SCFA increases with total faecal SCFA concentration in human studies. Although lactate is normally consumed by lactate-utilising bacteria, destabilisation of the microbial community associated with lactate accumulation can result in radically altered microbiota and metabolite profiles. A theoretical model based on microbial functional groups (MFG) was developed to better understand community dynamics. Consequences for nutritional research of our expanding knowledge of the microbial ecology of the human gut are considered.
ABSTRACT Termites decompose billions of tons of lignocellulosic material annually through the cellulolytic metabolism of their gut microbiota. However, the mechanisms by which cellulose degradation drives anaerobic metabolism of the gut microbiome remain poorly understood. Here, we demonstrate cellulose-driven extracellular electron transfer (EET) in both a termite gut-derived gram-positive cellulolytic bacterium, Ruminiclostridium cellobioparum subsp. termitidis CT1112, and the termite gut microbiome. CT1112 cells produced current in the presence of cellulose or cellobiose as the electron donor under potentiostatic conditions. This activity was strongly dependent on self-secreted redox mediators. EET was markedly impaired when stationary-phase CT1112 developed a thickened, multilayered cell wall, reducing accessibility to exogenously added redox mediators, such as riboflavin, and small redox-active molecules, such as diaminobenzidine. As a proof of concept, current production from cellulose was also observed in the termite gut microbiome, together with increases in the relative abundances of Bacillota, Bacteroidota, and Pseudomonadota. These results support the presence of EET-capable bacteria in the termite gut and suggest that EET contributes to redox balance within the steep redox gradients of the gut. Our study expands the environmental relevance of EET in carbon cycling and highlights termite-derived microbiomes as promising platforms for bioelectrochemical applications, including cellulolytic microbial fuel cells. IMPORTANCE Termites play major roles in carbon cycling in tropical ecosystems by decomposing lignocellulosic biomass with the help of their gut microbiota. However, the microbial physiology underlying this highly efficient cellulose conversion remains poorly understood. Here, we show that both a cellulolytic termite gut isolate and the termite gut microbiome are capable of extracellular electron transfer (EET) using cellulose and its derivatives as electron donors. These findings suggest that cellulose degradation in the termite gut is coupled to extracellular redox processes, expanding our understanding of how this globally important process proceeds in anaerobic environments. They also raise the possibility that EET contributes to redox homeostasis within the gut microenvironment and open new avenues for investigating the electrochemical physiology of termite gut microbes, including their ability to reduce dietary iron(III) minerals and their potential to participate in syntrophic interspecies electron transfer. Moreover, this work highlights termite-derived microbes as promising platforms for developing efficient cellulose-to-electricity conversion technologies. Termites play major roles in carbon cycling in tropical ecosystems by decomposing lignocellulosic biomass with the help of their gut microbiota. However, the microbial physiology underlying this highly efficient cellulose conversion remains poorly understood. Here, we show that both a cellulolytic termite gut isolate and the termite gut microbiome are capable of extracellular electron transfer (EET) using cellulose and its derivatives as electron donors. These findings suggest that cellulose degradation in the termite gut is coupled to extracellular redox processes, expanding our understanding of how this globally important process proceeds in anaerobic environments. They also raise the possibility that EET contributes to redox homeostasis within the gut microenvironment and open new avenues for investigating the electrochemical physiology of termite gut microbes, including their ability to reduce dietary iron(III) minerals and their potential to participate in syntrophic interspecies electron transfer. Moreover, this work highlights termite-derived microbes as promising platforms for developing efficient cellulose-to-electricity conversion technologies.
Xiao Deng, Akihiro Okamoto· Applied and Environmental Mi...· 0 citations
Anaerobic gut fungi (AGF) are key degraders of plant biomass in ruminants, yet there is limited knowledge of how AGF respond to mixtures of plant-derived sugars. Here, we assessed monosaccharide and disaccharide utilisation by Neocallimastix frontalis CoB3, Caecomyces communis SHB, and Piromyces edwardsiae SHC, which are abundant in the rumen microbiome. While all AGF isolates shared a core set of sugars that supported growth, they had different hierarchies of uptake. Co-substrate experiments using glucose and lignocellulose-derived sugars revealed species-specific responses, with N. frontalis displaying a novel concentration-dependent co-utilisation of glucose and mannose, whereas growth of P. edwardsiae was inhibited under the same conditions, and C. communis exhibited growth inhibition in glucose and xylose co-substrate cultures. Together, these findings demonstrate functional diversity in monosaccharide and disaccharide metabolism amongst the AGF investigated here. Understanding such sugar utilisation phenotypes provides a foundation for evaluating AGF isolate suitability for lignocellulosic biomass valorisation.
J. L. Matthews, Hannah Haupt, Stephen C. Fry et al.· bioRxiv· 0 citations
Lactic acid bacteria (LAB) represent major significance in microbiology and food science due to their crucial roles in food fermentation, extensive metabolic diversity, and their close association to human health. Detailed phylogenetic categorization and strain characterisation of LAB are essential for optimizing conventional and industrial fermentations, as well as for future functional food and biotechnological applications. This paper thoroughly examines the historical evolution, phylogenetic categorization, morphological, physiological, and functional attributes of the major genera of LAB. The transition from the first phenotypic-based categorization of LAB to current phylogenetic classifications utilizing 16S rRNA gene sequences and sophisticated genomic methodologies is elucidated comprehensively. The division of the genus Lactobacillus into 23 new genera and the union of the Lactobacillaceae and Leuconostocaceae families, based on whole genome sequencing and polyphasic approaches, are regarded as a significant milestone in LAB taxonomy. The links between this reclassification and metabolic profiles, ecological adaptations, and evolutionary relationships are discussed. This review compares the fermentative metabolic pathways, growth requirements, stress tolerance, and technological functions in food systems of the genera Lactobacillus, Lactococcus, Leuconostoc, Streptococcus, Pediococcus, Oenococcus, Enterococcus, Weissella, Vagococcus, and Tetragenococcus.
Many microorganisms are refractory to laboratory cultivation. One possible explanation, known as the great plate count anomaly, is metabolic dependencies among community members. However, systematic studies of these interactions in communities like soil are missing, hindering advances in understanding these ecologically important ecosystems. Here, we address this issue by systematically analysing 6,931 bacterial isolates of 27 soil microbial communities. We find that the growth of up to 50% of all community members depended essentially on supplementation with amino acids, vitamins, or nucleotides. In 73% of cases, supplementation with multiple amino acids was necessary. Genomic analysis of 62 strains revealed that accumulation of insertion sequences and specific gene loss was associated with the observed auxotrophies. Finally, genome-scale metabolic models, computational analyses, and cocultivation experiments demonstrated that other co-occurring genotypes complemented the metabolic needs of auxotrophs, thus facilitating their growth. Our results demonstrate that soil bacteria exist within integrated metabolic networks, which hampers their cultivation.
Ghada Yousif, Francisco Zorrilla, Swagatika Dash et al.· bioRxiv· 9 citations· ⚡1
Lactate, the major acidic end-product of carbohydrate metabolism in the oral microbiome, has long been recognized as a key driver of tooth demineralization by lowering the tooth surface pH below the critical threshold for enamel dissolution. Within the framework of the ecological plaque hypothesis, this frequent and prolonged acidification contributes to dysbiosis by favoring acidogenic and aciduric microorganisms. However, accumulating evidence indicates that microbiome-derived lactate plays broader roles in both microbial ecology and host physiology. This review synthesizes current knowledge on the multifaceted functions of lactate within the oral microbiome-host axis. Lactate produced by saccharolytic bacteria, mainly including Streptococcus, Actinomyces, and Lactobacillus, as well as Rothia and Gemella, is extensively used by commensal taxa, including Veillonella, Neisseria, Rothia, and Streptococcus oligofermentans, and is primarily converted into acetate, propionate, and carbon dioxide. These cross-feeding interactions form integral metabolic networks within oral biofilms that are tightly coupled to the production of bioactive molecules, including nitrite, hydrogen peroxide, and hydrogen sulfide, contributing to microbial ecological homeostasis. Nitrite may further enter the systemic circulation and exert physiological effects, such as peripheral vasodilation via nitric oxide production through the nitrate-nitrite-nitric oxide pathway. Furthermore, in addition to directly damaging host cells at high concentrations, lactate may function as a signaling molecule through hydroxycarboxylic acid receptor 1 on host cells, potentially modulating cellular responses by regulating metabolic and signal transduction pathways. Lactate is also transported into cells via monocarboxylate transporters, where it serves as a metabolic substrate for redox regulation and induces epigenetic modifications through histone and non-histone protein lactylation, thereby affecting host cell functions. These multifaceted functions highlight lactate as a metabolic and signaling hub in the oral microbiome-host axis. The modulation of the lactate flux, rather than simply inhibiting microbial lactate production, may offer a new strategy for maintaining and promoting oral and systemic health.
N. Takahashi· Journal of dentistry researc...· 0 citations
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