Mycobacterium smegmatis | EPFL Graph Search

Mycobacterium smegmatis est une espèce bactérienne acido-résistante du phylum Actinobacteria et du genre Mycobacterium. Ce microbe est long de et présente une forme de bacille ; il peut être coloré par la méthode Ziehl-Neelsen et la méthode fluorescente auramine-rhodamine. Il a été signalé pour la première fois en novembre 1884 par Lustgarten, qui a trouvé un bacille avec la coloration apparente de bacilles tuberculeux dans les chancres syphilitiques. Par la suite, Alvarez et Tavel ont trouvé des organismes similaires à ceux décrits par Lustgarten également dans les sécrétions génitales normales (smegma). Cet organisme a été nommé plus tard M. smegmatis. vignette |Plaques d'un virus isolé d'un tas de compost près de l'UCLA. La bactérie est M. smegmatis. M. smegmatis est généralement considéré comme un micro-organisme non pathogène ; cependant, dans certains cas très rares, il peut provoquer une maladie. M. smegmatis est utile pour l'analyse de recherche d'autres espèces de Mycobactéria dans des expériences de laboratoire. M. smegmatis est couramment utilisé dans les travaux sur le genre Mycobacterium car il est du type « croissance rapide » et non pathogène. M. smegmatis est un modèle simple, facile à travailler, c'est-à-dire avec un temps de doublement rapide et ne nécessite qu'un laboratoire de niveau de biosécurité 1. Le temps et les infrastructures lourdes nécessaires pour travailler avec des espèces pathogènes ont incité les chercheurs à utiliser M. smegmatis comme modèle pour les espèces mycobactériennes. Cette espèce partage plus de 2000 gènes homologues avec M. tuberculosis et partage la même structure de paroi cellulaire particulière que M. tuberculosis et d'autres espèces mycobactériennes. Il est également capable d'oxyder le monoxyde de carbone en aérobie, tout comme M. tuberculosis. La découverte de plasmides, de phages et d'éléments génétiques mobiles a permis la construction de systèmes dédiés d'inactivation de gènes et de rapporteurs de gènes. La souche M.

Coordination between cell growth, division and chromosome replication cycles in mycobacteria

Gaëlle Madeleine Vuaridel

Propagation of microorganisms is based on three fundamental processes: cell growth, DNA replication, and cell division. Although important for antibacterial drug development, these processes are poorly understood in Actinobacteria, a medically important phylum that includes Mycobacterium tuberculosis. Using microfluidic cultures and time-lapse microscopy, we studied single-cell growth, DNA replication, and cell division in the model organism Mycobacterium smegmatis.M. smegmatis is rod-shaped and grows by tip elongation in a biphasic manner due to a "new end take-off" (NETO) event. We find that pole elongation speed is increased and NETO occurs earlier in fast-growing cells than in slow-growing cells. As a consequence of variable timing of NETO, single-cell growth can be monophasic, biphasic, or triphasic. We propose that cells optimize pole growth speed and the timing of NETO to maximize their overall growth.We show that fast-growing cells initiate DNA replication earlier than slow-growing cells. We also find that single-cell growth speed is linked to cell-cycle progression, which is similar when comparing cells growing at the same speed under different conditions. We also report that multifork replication occurs when the time between DNA replication initiation events is shorter than the C period, which may occur even in slow-growing cells with interdivision times longer than the C period.Division site selection in many bacteria is governed by the nucleoid occlusion (Noc) and minicell (Min) systems. Mycobacteria do not encode homologs of these proteins and have no known mechanism for division site selection. We found that the DNA replisome and cell division ring colocalize and move together in a biphasic trajectory determined by the chromosome partitioning (Par) system. We propose a model in which Par-dependent movement of the replisome and division ring ultimately determines the site of cell division.Coordination of cell growth and division is required for cell size homeostasis. Three models of division control have been proposed: sizer (cells divide after reaching a critical size), timer (cells divide at a certain time after birth), and adder (cells add a specific amount of mass before dividing). We show that the single-cell growth model (exponential, linear, or bilinear) constrains the possible division control models. Thus, it is crucial to know the true model of single-cell growth in order to distinguish the true mechanism of cell size homeostasis.

EPFL2021

Revealing Antibiotic Tolerance of the Mycobacterium smegmatis Xanthine/Uracil Permease Mutant Using Microfluidics and Single-Cell Analysis

John McKinney, Neeraj Dhar, Meltem Elitas

To reveal rare phenotypes in bacterial populations, conventional microbiology tools should be advanced to generate rapid, quantitative, accurate, and high-throughput data. The main drawbacks of widely used traditional methods for antibiotic studies include low sampling rate and averaging data for population measurements. To overcome these limitations, microfluidic-microscopy systems have great promise to produce quantitative single-cell data with high sampling rates. Using Mycobacterium smegmatis cells, we applied both conventional assays and a microfluidic-microscopy method to reveal the antibiotic tolerance mechanisms of wild-type and msm2570::Tn mutant cells. Our results revealed that the enhanced antibiotic tolerance mechanism of the msm2570::Tn mutant was due to the low number of lysed cells during the antibiotic exposure compared to wild-type cells. This is the first study to characterize the antibiotic tolerance phenotype of the msm2570::Tn mutant, which has a transposon insertion in the msm2570 gene-encoding a putative xanthine/uracil permease, which functions in the uptake of nitrogen compounds during nitrogen limitation. The experimental results indicate that the msm2570::Tn mutant can be further interrogated to reveal antibiotic killing mechanisms, in particular, antibiotics that target cell wall integrity.

MDPI2021

Coordination between cell growth, division and chromosome replication cycles in mycobacteria

Gaëlle Madeleine Vuaridel

EPFL2021