Pyomelanin biosynthetic pathway in pigment-producer strains from the pandemic Acinetobacter baumannii IC-5

Abstract

BACKGROUND Acinetobacter baumannii outbreaks have been associated with pandemic International Clones (ICs), but the virulence factors involved with their pathogenicity are sparsely understood. Pigment production has been linked with bacterial pathogenicity, however, this phenotype is rarely observed in A. baumannii. OBJECTIVES This study aimed to characterise the reddish-brown pigment produced by A. baumannii strains, and to determine its biosynthetic pathway by genomic approaches. METHODS Pigment characterisation and antimicrobial susceptibility were conducted by phenotypic tests. The clonal relationship was obtained by pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The genome of an A. baumannii was obtained for characterisation of genes involved with pigment production. FINDINGS The pyomelanin was the pigment produced by A. baumannii. Strains were extensively drug resistant and belonged to the IC-5/ST79. The pyomelanin biosynthetic pathway was determined and presented a particular architecture concerning the peripheral (tyrB, phhB and hpd) and central (hmgB, hmgC and hmgR) metabolic pathway genes. The identification of a distant HmgA homologue, probably without dioxygenase activity, could explain pyomelanin production. Virulence determinants involved with adherence (csuA/BABCDE and a T5bSS-carrying genomic island), and iron uptake (basABCDEFGHIJ, bauABCDEF and barAB) were characterised. MAIN CONCLUSION There is a biosynthetic pathway compatible with the pyomelanin production observed in persistent A. baumannii IC-5 strains.

Pyomelanin-Producing Brevundimonas vitisensis sp. nov., Isolated From Grape (Vitis vinifera L.)

“…Homogentisic acid is catabolized by a central metabolic pathway that involves three enzymes, homogentisate dioxygenase ( hmgA ; EC 1.13.11.5), fumarylacetoacetate hydrolase ( hmgB / fahA ), and maleylacetoacetate isomerase ( maiA / hmgC ), and then, final products are fumarate (EC 4.2.1.2) and acetoacetate ( Arias-Barrau et al, 2004 ). The pyomelanin production results from a defect in the catabolism pathway ( Fonseca et al, 2020 ). When hmgA levels are low (e.g., gene mutation, deletions, or overexpression of hmgR , HGA accumulates and secretes out of cells, and it lead to pyomelanin though HGA auto-oxidation and self-polymerization.…”

“…When hmgA levels are low (e.g., gene mutation, deletions, or overexpression of hmgR , HGA accumulates and secretes out of cells, and it lead to pyomelanin though HGA auto-oxidation and self-polymerization. ( Arias-Barrau et al, 2004 ; Rodríguez-Rojas et al, 2009 ; Wang et al, 2011 ; Fonseca et al, 2020 ). In the whole genome of strain GR-TSA-9 T , TetR family member hmgR (PA2010), which was previously shown to bind directly to the hmgA promoter and repress hmgA expression, blocks the central pathway and finally accumulates homogentisic acid and produces pyomelanin ( Figure 4A ).…”

Draft Genome Sequences and Genomic Analysis for Pigment Production in Bacteria Isolated from Blue Discolored Soymilk and Tofu

“…Pyomelanin is a water-soluble, dark brown pigment produced by various bacteria including some Pseudomonas species, and synthesis of this compound results from exposure to tyrosine or phenylalanine in the environment that can be taken up, degraded, and utilized to accumulate homogentisic acid (HGA) 10 , 34 , 35 . Like other melanins, pyomelanin is formed by the enzymatic oxidation and subsequent polymerization of phenolic and/or indolic compounds 25 , 36 .…”

“…Aliquots of these isolates were frozen in 25% glycerol in cryovials for long-term storage, and were used for additional investigations. Isolates UCD_MED3 and UCD_MED7 were subcultured on Petri plates and the surfaces of agar deep tubes containing Mueller Hinton agar (MHA), a medium shown to promote pyomelanin production by some bacteria [9,10]. Following incubation at room temperature for 48 hours MHA plates and agar deep tubes were observed for production of brown pigment, and also exposed to ultraviolet irradiation to detect fluorescence.…”

Description of a Rare Pyomelanin-Producing Carbapenem-Resistant Acinetobacter baumannii Strain Coharboring Chromosomal OXA-23 and NDM-1

“…Pigmentation of clinical strains of CRAB has rarely been observed. The presence of a reddish-brown pigment, pyomelanin, causes a quite rare phenotype, reported only twice ( 10 , 11 ). The overproduction of the pyomelanin is caused due to changes in the tyrosine metabolic pathway and is based on the deletion of the hmgA encoding homogentisate dioxygenase (HmgA) by IS Aba1 ( 11 ).…”