Biology subjects

Carvalho, L. P.

Publications and source records attributed to Carvalho, L. P..

3 recordsLinked to original sources

bioRxiv2018

Nitrogen utilisation by the metabolic generalist pathogen Mycobacterium tuberculosis

Bacterial metabolism is fundamental to pathogenesis and has a dominant effect on bacterial killing by antibiotics. Here we explore how Mycobacterium tuberculosis utilises amino acids as nitrogen sources, using a combination of bacterial physiology and stable isotope tracing coupled to liquid chromatography mass spectrometry metabolomics methods. Our results define core properties of the nitrogen metabolic network from M. tuberculosis, such as: (i) the lack of homeostatic control of amino acid pool sizes; (ii) similar rates of utilisation of different amino acids as sole nitrogen sources; (iii) improved nitrogen utilisation from amino acids compared to ammonium; and (iv) co-metabolism of nitrogen sources. Finally, we discover that alanine dehydrogenase, is involved in ammonium assimilation in M. tuberculosis, in addition to its essential role in alanine utilisation. This study represents the first in-depth analysis of nitrogen source utilisation by metabolic generatlist M. tuberculosis and reveals a flexible metabolic network with characteristics that are likely product of evolution in the human host.

microbiology↗

bioRxiv2018

Antibiotic resistance evasion is explained by rare mutation frequency and not by lack of compensatory mechanisms

Drug resistant infections represent one of the most challenging medical problems of our time. D-cycloserine is an antibiotic used for decades without appearance and dissemination of antibiotic resistant strains, making it an ideal model compound to understand what drives resistance evasion. We investigated why Mycobacterium tuberculosis fails to become resistant to D-cycloserine. To address this question we employed a combination of bacterial genetics, genomics, biochemistry and fitness analysis in vitro, in macrophages and in mice. Altogether, our results suggest that the ultra-low mutation frequency associated with D-cycloserine resistance is the dominant factor delaying the appearance of clinical resistance to this antibiotic in bacteria infecting humans, and not lack of potential compensatory mechanisms.\n\nOne Sentence SummaryWe show that the lack of D-cycloserine resistance in Mycobacterium tuberculosis is due its ultra-low mutation frequency rather than lack of compensatory mechanisms.

microbiology↗

bioRxiv2018

Discovery of a novel stereospecific β-hydroxyacyl-CoA lyase/thioesterase shared by three metabolic pathways in Mycobacterium tuberculosis

The vast number of poorly characterised enzymes in Mycobacterium tuberculosis (Mtb) is one of the key barriers precluding a better understanding of the biology that underpins pathogenesis. Here, we investigated the Mtb orphan enzyme Rv2498c to delineate its physiological role. Our results from in vitro enzymatic assays, phylogenetic analysis, X-ray crystallography and in vivo Mtb experiments, de-orphan Rv2498c as a multi-functional {beta}-hydroxyacyl-CoA lyase/thioesterase ({beta}-HAClyase/thioesterase) that participates in three different metabolic pathways: L-leucine catabolism, itaconate dissimilation, and glyoxylate shunt. Moreover, the deletion of the rv2498c gene from the Mtb genome resulted in attenuation in the mouse model compared to infection with the parent strain. To the best of our knowledge, this is the first report of an (R)-3-hydroxyl-3-methylglutaryl-CoA for leucine catabolism and an itaconate-specific resistance mechanism in Mtb.

biochemistry↗