Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.12.247981v1?rss=1 Authors: Muir, A., Gurung, I., Cehovin, A., Bazin, A., Vallenet, D., Pelicic, V. Abstract: One of the most important challenges in biology is to determine the function of millions of genes of unknown function. Even in model bacterial species, there is a sizeable proportion of such genes, which has important theoretical and practical consequences. Here, we constructed a complete collection of defined mutants - named NeMeSys - in the important human pathogen Neisseria meningitidis, consisting of individual mutants in 1,584 non-essential genes. This effort identified 391 essential meningococcal genes - highly conserved in other bacteria - leading to a full panorama of the minimal genome in this species, associated with just four underlying basic biological functions: 1) expression of genome information, 2) preservation of genome information, 3) cell membrane structure/function, and 4) cytosolic metabolism. Subsequently, we illustrated the utility of the NeMeSys collection for determining gene function by identifying 1) a novel and conserved family of histidinol-phosphatase, 2) all genes, including three new ones, involved in the biology of type IV pili, a widespread virulence factor, and 3) several conditionally essential genes found in regions of genome plasticity, likely to encode antitoxins and/or immunity proteins. These findings have widespread implications in bacteria. The NeMeSys collection is an invaluable resource paving the way for a global phenotypic landscape in a major human bacterial pathogen. Copy rights belong to original authors. Visit the link for more info