Construction of a complete set of Neisseria meningitidis defined mutants - the NeMeSys collection - and its use for the phenotypic profiling of the genome of an important human pathogen

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.