Human Microbiome Project | EPFL Graph Search

The Human Microbiome Project (HMP) was a United States National Institutes of Health (NIH) research initiative to improve understanding of the microbiota involved in human health and disease. Launched in 2007, the first phase (HMP1) focused on identifying and characterizing human microbiota. The second phase, known as the Integrative Human Microbiome Project (iHMP) launched in 2014 with the aim of generating resources to characterize the microbiome and elucidating the roles of microbes in health and disease states. The program received $170 million in funding by the NIH Common Fund from 2007 to 2016. Important components of the HMP were culture-independent methods of microbial community characterization, such as metagenomics (which provides a broad genetic perspective on a single microbial community), as well as extensive whole genome sequencing (which provides a "deep" genetic perspective on certain aspects of a given microbial community, i.e. of individual bacterial species). The latter served as reference genomic sequences — 3000 such sequences of individual bacterial isolates are currently planned — for comparison purposes during subsequent metagenomic analysis. The project also financed deep sequencing of bacterial 16S rRNA sequences amplified by polymerase chain reaction from human subjects. Prior to the HMP launch, it was often reported in popular media and scientific literature that there are about 10 times as many microbial cells and 100 times as many microbial genes in the human body as there are human cells; this figure was based on estimates that the human microbiome includes around 100 trillion bacterial cells and an adult human typically has around 10 trillion human cells. In 2014 the American Academy of Microbiology published a FAQ that emphasized that the number of microbial cells and the number of human cells are both estimates, and noted that recent research had arrived at a new estimate of the number of human cells at around 37 trillion cells, meaning that the ratio of microbial to human cells is probably about 3:1.

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Leonardo Filipe Lemos Rocha

The bacterium Vibrio cholerae is the causative agent of the diarrheal disease cholera, which affects millions of people every year. Apart from being a human pathogen, V. cholerae is also a common member of aquatic habitats. Whilst the mechanism that allow it to transit from an environmental to a pathogenic lifestyle is still understudied, it is well established that virulence induction is linked to the bacterium's ability to sense its surroundings. Therefore, this thesis aimed to shed new light on the general sensing capacity of V. cholerae and its adaptation to the surrounding environment. Specifically, we explored the functions of the virulence-associated regulatory two-component system VarS/VarA, which was shown to regulate the major virulence factors of V. cholerae. In this thesis, we identified a new function of this regulatory system in modulating the pathogen's cellular shape. Precisely, we demonstrated that a strain lacking the response regulator VarA loses its normal curve-shaped morphology and transits to spherical shape during stationary phase of growth. This rounding phenotype was not observed on cells lacking the sensor histidine kinase VarS, which suggests the existence of additional VarA activators. Through analysis of the cells's peptidoglycan (PG), we found that the cause of the atypical shape was due to high abundance of dipeptides and reduced peptide cross-links. This abnormal PG composition and consequent cell rounding could be abrogated through cell wall recycling of wild type-derived PG subunits. Through a transposon mutagenesis screen, we identified the carbon storage regulator A (CsrA) as a key player in this phenotype. We showed that varA-deficient cells have an increased activity of CsrA, which led to an overproduction of the aspartate ammonia lyase enzyme (AspA). Our results indicate that AspA overproduction likely reduced the pool of aspartate in varA-deficient cells, which subsequently impaired the biosynthesis of the cell wall precursor meso-diaminopimelic acid. Ultimately, this compromised production of PG precursors resulted in the altered PG composition and consequent cell rounding. Furthermore, and consistent with findings in Enterobacteriaceae, our results also suggest that the VarA-CsrA regulatory circuit modulates chemotaxis and motility in V. cholerae. Finally, in two different collaborative studies, we also addressed how V. cholerae might interact with other bacteria in the environment taking bacterial antagonism strategies into consideration. Firstly, we showed that a subset of human gut microbiota isolates is able to withstand type VI secretion system (T6SS)-mediated attacks by V. cholerae in an immunity protein-independent manner. Moreover, our preliminary data indicates a superior T6SS-mediated killing potential from a specific environmental strain of V. cholerae compared to a particular toxigenic strain. Secondly, we demonstrated that the environmental V. cholerae strain SA7G harbors a specific plasmid, pSA7G1, that confers a competitive advantage over neighboring bacteria likely through type IV secretion system-mediated killing. Collectively, the findings of this thesis contribute to better understanding how V. cholerae adapts to the environment, namely with specific sensing-response mechanisms such as the VarA-CsrA signaling pathway.

EPFL2022

Trans‐seeding of Alzheimer‐related tau protein by a yeast prion

Henning Paul-Julius Stahlberg, Zhiva Skachokova

Abnormal tau protein aggregates constitute a hallmark of Alzheimer's disease. The mechanisms underlying the initiation of tau aggregation in sporadic neurodegeneration remain unclear. Here we investigate whether a non-human prion can seed tau aggregation. Due to their structural similarity with tau aggregates, we chose Sup35NM yeast prion domain fibrils for explorative tau seedings. Upon in vitro incubation with tau monomers, Sup35NM fibrils promoted the formation of morphologically distinct tau fibril strains. In vivo, intrahippocampal inoculation of Sup35NM fibrils accentuated tau pathology in P301S tau transgenic mice. Thus, our results provide first in vivo evidence for heterotypic cross-species seeding of a neurodegenerative human prion-like protein by a yeast prion. This opens up the conceptual perspective that non-mammalian prions present in the human microbiome could be involved in the initiation of protein misfolding in neurodegenerative disorders, a mechanism for which we propose the term “trans-seeding.”

2022

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Leonardo Filipe Lemos Rocha

EPFL2022