Roux-en-Y gastric bypass (RYGB) results in rapid weight loss, reduced adiposity, and improved glucose metabolism. These effects are not simply attributable to decreased caloric intake or absorption, but the mechanisms linking rearrangement of the gastrointestinal tract to these metabolic outcomes are largely unknown. Studies in humans and rats have shown that RYGB restructures the gut microbiota, prompting the hypothesis that some of the effects of RYGB are caused by altered host-microbial interactions. To test this hypothesis, we used a mouse model of RYGB that recapitulates many of the metabolic outcomes in humans. 16S ribosomal RNA gene sequencing of murine fecal samples collected after RYGB surgery, sham surgery, or sham surgery coupled to caloric restriction revealed that alterations to the gut microbiota after RYGB are conserved among humans, rats, and mice, resulting in a rapid and sustained increase in the relative abundance of Gammaproteobacteria (Escherichia) and Verrucomicrobia (Akkermansia). These changes were independent of weight change and caloric restriction, were detectable throughout the length of the gastrointestinal tract, and were most evident in the distal gut, downstream of the surgical manipulation site. Transfer of the gut microbiota from RYGB-treated mice to nonoperated, germ-free mice resulted in weight loss and decreased fat mass in the recipient animals relative to recipients of microbiota induced by sham surgery, potentially due to altered microbial production of short-chain fatty acids. These findings provide the first empirical support for the claim that changes in the gut microbiota contribute to reduced host weight and adiposity after RYGB surgery.

Non-enzymatic, template-directed synthesis of nucleic acids is a paradigm for self-replicating systems. The evolutionary dynamics of such systems depend on several factors, including the mutation rates, relative replication rates, and sequence characteristics of mutant sequences. We measured the kinetics of correct and incorrect monomer insertion downstream of a primer-template mismatch (mutation), using a range of backbone structures (RNA, DNA, and LNA templates and RNA and DNA primers) and two types of 5′-activated nucleotides (oxyazabenzotriazolides and imidazolides, i.e., nucleoside 5’-phosphorimidazolides). Our study indicated that for all systems studied, an initial mismatch was likely to be followed by another error (54-75% of the time) and extension after a single mismatch was generally 10-100 times slower than extension without errors. If the mismatch was followed by a matched base pair, the extension rate recovered to nearly normal levels. Based on these data, we simulated nucleic acid replication in silico, which indicated that a primer suffering an initial error would lag behind properly extended counterparts due to a cascade of subsequent errors and kinetic stalling, with the typical mutational event consisting of several consecutive errors. Our study also included different sequence contexts, which suggest the presence of cooperativity among monomers affecting both absolute rate (by up to two orders of magnitude) and fidelity. The results suggest that molecular evolution in enzyme-free replication systems would be characterized by large ‘leaps’ through sequence space rather than isolated point mutations, perhaps enabling rapid exploration of diverse sequences. The findings may also be useful for designing self-replicating systems combining high fidelity with evolvability.

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