Microbial protein metabolism in the monogastric gastrointestinal tract: a review

Dietary and endogenous protein that become available for the microbiota in the hindgut can be metabolized via different routes. They can become building blocks for the microbial cells or enter different catabolic pathways. Protein degradation via fermentation pathways is seen as a non-preferred route as it results in the formation and release of metabolites that can interfere with biological systems in the host and can have deleterious outcomes. Reducing protein fermentation and guiding the metabolism towards less toxic end-products might be possible targets for improving host health. To do so, more knowledge on factors manipulating the process of microbial protein metabolism, including on substrate availability, microbial composition and segmental differences in the hindgut, is required.

Particle-associated and free-living microbial assemblages are distinct in a permanently redox-stratified freshwater lake

Microbial assemblages associated with biogenic particles are phylogenetically distinct from free-living counterparts, yet biogeochemically coupled. Compositions may vary with organic carbon and inorganic substrate availability and with redox conditions, which determine reductant and oxidant availability. To explore microbial assemblage compositional responses to steep oxygen and redox gradients and seasonal variability in particle and substrate availability, we analyzed taxonomic compositions of particle-associated (PA) and free-living (FL) bacteria and archaea in permanently redox-stratified Fayetteville Green Lake. PA and FL assemblages (> 2.7 μm and 0.2-2.7 μm) were surveyed at the peak (July) and end (October) of concurrent cyanobacteria, purple and green sulfur bacteria blooms that result in substantial vertical fluxes of particulate organic carbon. Assemblage compositions varied significantly among redox conditions and size fractions (PA or FL). Temporal differences were only apparent among samples from the mixolimnion and oxycline, coinciding with seasonal hydrographic changes. PA assemblages of the mixolimnion and oxycline shifted from aerobic heterotrophs in July to fermenters, iron-reducers, and denitrifiers in October, likely reflecting seasonal variability in photoautotroph biomass and inorganic nitrogen. Within a light-scattering layer spanning the lower oxycline and upper monimolimnion, photoautotrophs were more abundant in July than in October, when Desulfocapsa, a sulfate-reducing and sulfur-disproportionating bacterium, and Chlorophyte chloroplasts were abundant in PA assemblages. In this layer, microbial activity and cell concentrations were also highest. Below, the most abundant resident taxa were sulfate-reducing bacteria and anaerobic respirers. Results suggest PA and FL assemblage niche partitioning interconnects multiple elemental cycles that involve particulate and dissolved phases.

Kinetic compartmentalization by unnatural reaction for itaconate production

Physical compartmentalization of metabolisms using membranous organelles in eukaryotes is helpful for chemical biosynthesis to ensure the availability of substrates from competitive metabolic reactions. Bacterial hosts lack such a membranous system, which is one of the major limitations for efficient metabolic engineering. Here, we introduced kinetic compartmentalization as an alternative strategy to enable substrate availability from competitive reactions. This method utilizes a non-natural biochemical reaction performed by an engineered enzyme to kinetically isolate the metabolic pathways and ensure substrate availability for the desired reaction. As a proof of concept, we could successfully demonstrate kinetic separation for efficient itaconate production from acetate in Escherichia coli, mimicking the native mitochondrial membrane system in Aspergillus species. Despite the utilization of the non-preferred carbon source, kinetic compartmentalization could lead to substantial increases of itaconate in both yield and titer, suggesting enough potential of our strategy for broad applications in diverse engineering.

Acute melatonin administration improves exercise tolerance and the metabolic recovery after exhaustive effort

The present study investigated the effects of acute melatonin administration on the biomarkers of energy substrates, GLUT4, and FAT/CD36 of skeletal muscle and its performance in rats subjected to exhaustive swimming exercise at an intensity corresponding to the maximal aerobic capacity (tlim). The incremental test was performed to individually determine the exercise intensity prescription and 48 h after, the animals received melatonin (10 mg·kg−1) or vehicles 30 min prior to tlim. Afterwards, the animals were euthanized 1 or 3 h after the exhaustion for blood and muscles storage. The experiment 1 found that melatonin increased the content of glycogen and GLUT4 in skeletal muscles of the animals that were euthanized 1 (p < 0.05; 22.33% and 41.87%) and 3 h (p < 0.05; 37.62% and 57.87%) after the last procedures. In experiment 2, melatonin enhanced the tlim (p = 0.01; 49.42%), the glycogen content (p < 0.05; 40.03%), GLUT4 and FAT/CD36 in exercised skeletal muscles (F = 26.83 and F = 25.28, p < 0.01). In summary, melatonin increased energy substrate availability prior to exercise, improved the exercise tolerance, and accelerated the recovery of muscle energy substrates after the tlim, possibly through GLUT4 and FAT/CD36.