Biology subjects

de Wet, T. J.

Publications and source records attributed to de Wet, T. J..

4 recordsLinked to original sources

bioRxiv2021

The mycobacterial mutasome: composition and recruitment in live cells

A DNA damage-inducible mutagenic gene cassette has been implicated in the emergence of drug resistance in Mycobacterium tuberculosis during anti-tuberculosis (TB) chemotherapy. However, the molecular composition and operation of the encoded "mycobacterial mutasome" - minimally comprising DnaE2 polymerase and ImuA' and ImuB accessory proteins - remain elusive. Following exposure of mycobacteria to DNA damaging agents, we observe that DnaE2 and ImuB co-localize with the DNA polymerase III {beta} subunit ({beta} clamp) in distinct intracellular foci. Notably, genetic inactivation of the mutasome in an imuBAAAAGG mutant containing a disrupted {beta} clamp-binding motif abolishes ImuB-{beta} clamp focus formation, a phenotype recapitulated pharmacologically by treating bacilli with griselimycin and in biochemical assays in which this {beta} clamp-binding antibiotic collapses pre-formed ImuB-{beta} clamp complexes. These observations establish the essentiality of the ImuB-{beta} clamp interaction for mutagenic DNA repair in mycobacteria, identifying the mutasome as target for adjunctive therapeutics designed to protect anti-TB drugs against emerging resistance.

microbiology↗

bioRxiv2020

De novo cobalamin biosynthesis, transport and assimilation and cobalamin-mediated regulation of methionine biosynthesis in Mycobacterium smegmatis

Cobalamin is an essential co-factor in all domains of life, yet its biosynthesis is restricted to some bacteria and archaea. Mycobacterium smegmatis, an environmental saprophyte frequently used as surrogate for the obligate human pathogen, M. tuberculosis, carries approximately 30 genes predicted to be involved in de novo cobalamin biosynthesis. M. smegmatis also encodes multiple cobalamin-dependent enzymes, including MetH, a methionine synthase which catalyses the final reaction in methionine biosynthesis. In addition to metH, M. smegmatis possesses a cobalamin-independent methionine synthase, metE, suggesting that enzyme selection - MetH or MetE - is regulated by cobalamin availability. Consistent with this notion, we previously described a cobalamin-sensing riboswitch controlling metE expression in M. tuberculosis. Here, we apply a targeted mass spectrometry-based approach to confirm de novo cobalamin biosynthesis in M. smegmatis during aerobic growth in vitro. We also demonstrate that M. smegmatis transports and assimilates exogenous cyanocobalamin (CNCbl; a.k.a. vitamin B12) and its precursor, dicyanocobinamide ((CN)2Cbi). Interestingly, the uptake of CNCbl and (CN)2Cbi appears restricted in M. smegmatis and dependent on the conditional essentiality of the cobalamin-dependent methionine synthase. Using gene and protein expression analyses combined with single-cell growth kinetics and live-cell time-lapse microscopy, we show that transcription and translation of metE are strongly attenuated by endogenous cobalamin. These results support the inference that metH essentiality in M. smegmatis results from riboswitch-mediated repression of MetE expression. Moreover, differences observed in cobalamin-dependent metabolism between M. smegmatis and M. tuberculosis provide some insight into the selective pressures which might have shaped mycobacterial metabolism for pathogenicity. IMPORTANCEAccumulating evidence suggests that alterations in cobalamin-dependent metabolism marked the evolution of Mycobacterium tuberculosis from an environmental ancestor to an obligate human pathogen. However, the roles of cobalamin in mycobacterial physiology and pathogenicity remain poorly understood. We used the non-pathogenic saprophyte, M. smegmatis, to investigate the production of cobalamin, transport and assimilation of cobalamin precursors, and the potential role of cobalamin in regulating methionine biosynthesis. We provide biochemical and genetic evidence confirming constitutive de novo cobalamin biosynthesis in M. smegmatis under standard laboratory conditions, in contrast with M. tuberculosis, which appears to lack de novo cobalamin biosynthetic capacity. We also demonstrate that the uptake of cyanocobalamin (vitamin B12) and its precursors is restricted in M. smegmatis, apparently depending on the need to service the co-factor requirements of the cobalamin-dependent methionine synthase. These observations support the utility of M. smegmatis as a model to elucidate key metabolic adaptations enabling mycobacterial pathogenicity.

microbiology↗

bioRxiv2020

Arrayed CRISPRi and Quantitative Imaging Describe the Morphotypic Landscape of Essential Mycobacterial Genes

Mycobacterium tuberculosis possesses a large number of genes of unknown or merely predicted function, undermining fundamental understanding of pathogenicity and drug susceptibility. To address this challenge, we developed a high-throughput functional genomics approach combining inducible CRISPR-interference and image-based analyses of morphological features and sub-cellular molecular localizations in the related non-pathogen, M. smegmatis. Applying automated imaging and analysis to an arrayed library of 272 essential gene knockdown mutants, we derive robust, quantitative descriptions of bacillary morphologies consequent on gene silencing. Leveraging statistical-learning, we demonstrate that functionally related genes cluster by morphotypic similarity and that this information can be used to infer gene function. Exploiting this observation, we reveal a previously unknown restriction-modification system, and identify filamentation as a defining mycobacterial response to histidine starvation. Our results support the application of large-scale image-based analyses for mycobacterial functional genomics, simultaneously establishing the utility of this approach for drug mechanism-of-action studies.

microbiology↗

bioRxiv2018

CRISPRi-Seq for the Identification and Characterisation of Essential Mycobacterial Genes and Transcriptional Units

High-throughput essentiality screens have enabled genome-wide assessments of the genetic requirements for growth and survival of a variety of bacteria in different experimental models. The reliance in many of these studies on transposon (Tn)-based gene inactivation has, however, limited the ability to probe essential gene function or design targeted screens. We interrogated the potential of targeted, large-scale, pooled CRISPR interference (CRISPRi)-based screens to extend conventional Tn approaches in mycobacteria through the capacity for positionally regulable gene repression. Here, we report the utility of the \"CRISPRi-Seq\" method for targeted, pooled essentiality screening, confirming strong overlap with Tn-Seq datasets. In addition, we exploit this high-throughput approach to provide insight into CRISPRi functionality. By interrogating polar effects and combining image-based phenotyping with CRISPRi-mediated depletion of selected essential genes, we demonstrate that CRISPRi-Seq can functionally validate Transcriptional Units within operons. Together, these observations suggest the utility of CRISPRi-Seq to provide insights into (myco)bacterial gene regulation and expression on a genome-wide scale.

microbiology↗