Centenarians, or individuals who have lived more than a century, represent the ultimate model of successful longevity associated with decreased susceptibility to ageing-associated illness and chronic inflammation [1][2][3] . The gut microbiota is considered to be a critical determinant of human health and longevity [4][5][6][7][8] . Here we show that centenarians (average 107 yo) have a distinct gut microbiome enriched in microbes capable of generating unique secondary bile acids, including iso-, 3-oxo-, and isoallo-lithocholic acid (LCA), as compared to elderly (85-89 yo) and young (21-55 yo) controls. Among these bile acids, the biosynthetic pathway for isoalloLCA had not been described previously. By screening 68 bacterial isolates from a centenarian's faecal microbiota, we identified Parabacteroides merdae and Odoribacteraceae strains as effective producers of isoalloLCA. Furthermore, we generated and tested mutant strains of P. merdae to show that the enzymes 5a-reductase (5AR) and 3bhydroxysteroid dehydrogenase (3bHSDH) were responsible for isoalloLCA production. This secondary bile acid derivative exerted the most potent antimicrobial effects among the tested bile acid compounds against gram-positive (but not gram-negative) multidrug-resistant pathogens, including Clostridioides difficile and vancomycin-resistant Enterococcus faecium.These findings suggest that specific bile acid metabolism may be involved in reducing the risk of pathobiont infection, thereby potentially contributing to longevity. MainThe microbiome has long been recognized as a key player in determining the health status of ageing individuals through its role in controlling digestive functions, bone density, neuronal activity, immunity, and resistance to pathogen infection [9][10][11][12][13] . Microbial consortia in elderly individuals often show increased interindividual variability and reduced diversity, and are thus being linked to immunosenescence, chronic systemic inflammation, and frailty 6,14 . An integrated understanding of the dynamic balance and functions of microbial members with respect to ageing is essential for establishing a strategy toward rational manipulation of the microbiota for restoring and/or maintaining tissue homeostasis and overall health.Centenarians (aged 100 years and older) are known to be less susceptible to age-related diseases including hypertension, diabetes, obesity, and cancer 3,15 . Moreover, centenarians have likely survived periods of hunger and several bouts with infectious diseases such as influenza, tuberculosis, shigellosis, and salmonellosis 16 . It has been postulated that there are centenarian-specific members of the gut microbiota which, rather than representing a mere consequence of ageing, might actively contribute to maintaining homeostasis, resilience, and healthful ageing [4][5][6]8 . In this study, we aimed

The human body is colonized by microorganisms from all three domains of life, with the gastrointestinal tract exhibiting the greatest microbial density and diversity 1-3. Gut microorganisms outnumber the host by more than 25-fold in terms of genetic composition 4. Unsurprisingly, this vast microbial ecosystem interacts intimately and, for the most part, mutualistically with its human host, performing essential metabolic functions such as polysaccharide fermentation and vitamin biosynthesis that affect multiple aspects of host physiology, including maturation of the immune system 5. As such, perturbation of the homeostatic microbiota composition (known as dysbiosis 6,7) has been correlated with a myriad of diseases including inflammatory bowel disease (IBD) 8 , cancer 9 , autism 10 and metabolic conditions such as diabetes 11 , cardiovascular disease 12 and obesity 13-15 (reviewed extensively elsewhere 6,16,17). Culture-independent metagenomic approaches to characterize the microbiota, enabled by next-generation sequencing, have increased the sensitivity and power of such associative studies by enabling high-throughput analysis 18. However, although certain microbiota configurations are associated with disease, defining the composition of a healthy microbiota has proved difficult. Bacteroidetes and Firmicutes together account for the majority of gut commensals in healthy adults, but the relative abundance of species within these phyla, and even of the phyla themselves, varies greatly from person to person 19. Accordingly, the seminal Human Microbiome Project revealed that there is no core set of microbial taxa conserved across all people, precluding categorical classification of many commensal species as good or bad based on large-scale correlation analyses alone 2. In addition, while sequence-based microbiomewide association studies provide correlative support for the notion that commensals influence human health and disease, they address neither the causality nor the directionality of the host-microbiota relationship, as disease-associated dysbiosis could be a mere reflection of microbiota adaptation to pathophysiological host conditions. The recent shift towards causational studies has enabled the identification of bacterial species that directly contribute to host homeostasis in specific ways. In particular, the combination of two complementary reductionist approaches, that is, gnotobiotic and metabolite-based, has enabled a detailed mechanistic understanding of dysbiosis-mediated disease and microbiota-mediated immunomodulation 3,20-22 , in which specific bacterial species and their products play critical roles. Concurrently, advances in culture techniques along with high-resolution mass spectrometry have provided an additional lens through which to identify small molecules correlated with disease, setting the stage for more rigorous studies 23-25. The intestinal milieu is replete with small molecules produced by gut commensals, which can be either synthesized de novo or metabolized from dietary or host-deriv...

bMalaria is a vector-borne disease caused by the single-cell eukaryote Plasmodium. The infectious parasite forms are sporozoites, which originate from midgut-associated oocysts, where they eventually egress and reach the mosquito hemocoel. Sporozoites actively colonize the salivary glands in order to be transmitted to the mammalian host. Whether residence in the salivary glands provides distinct and vital cues for the development of infectivity remains unsolved. In this study, we systematically compared the infectivity of Plasmodium berghei sporozoites isolated from the mosquito hemocoel and salivary glands. Hemocoel sporozoites display a lower proportion of gliding motility but develop into liver stages when added to cultured hepatoma cells or after intravenous injection into mice. Mice infected by hemocoel sporozoites had blood infections similar to those induced by sporozoites liberated from salivary glands. These infected mice display indistinguishable systemic inflammatory cytokine responses and develop experimental cerebral malaria. When used as metabolically active, live attenuated vaccine, hemocoel sporozoites elicit substantial protection against sporozoite challenge infections. Collectively, these findings show that salivary gland colonization does not influence parasite virulence in the mammalian host when sporozoites are administered intravenously. This conclusion has important implications for in vitro sporozoite production and manufacturing of whole-sporozoite vaccines.

Neuronal PAS domain protein 2 (NPAS2) is a circadian rhythm-associated transcription factor with two heme-binding sites on two PAS domains. In the present study, we compared the optical absorption spectra, resonance Raman spectra, heme-binding kinetics and DNA-binding characteristics of the isolated fragment containing the N-terminal basic helix-loop-helix (bHLH) of the first PAS (PAS-A) domain of NPAS2 with those of the PAS-A domain alone. We found that the heme-bound bHLH-PAS-A domain mainly exists as a dimer in solution. The Soret absorption peak of the Fe(III) complex for bHLH-PAS-A (421 nm) was located at a wavelength 9 nm higher than for isolated PAS-A (412 nm). The axial ligand trans to CO in bHLH-PAS-A appears to be His, based on the resonance Raman spectra. In addition, the rate constant for heme association with apo-bHLH-PAS (3.3 x 10(7) mol(-1) x s(-1)) was more than two orders of magnitude higher than for association with apo-PAS-A (< 10(5) mol(-1) x s(-1)). These results suggest that the bHLH domain assists in stable heme binding to NPAS2. Both optical and resonance Raman spectra indicated that the Fe(II)-NO heme complex is five-coordinated. Using the quartz-crystal microbalance method, we found that the bHLH-PAS-A domain binds specifically to the E-box DNA sequence in the presence, but not in the absence, of heme. On the basis of these results, we discuss the mode of heme binding by bHLH-PAS-A and its potential role in regulating DNA binding.