Pyomelanin production by Pseudomonas aeruginosa. I. Transformation of pyomelanin productivity

Chronic Polymicrobial Infectious Melanonychia Striata

CASE

A 62-year-old man presented with a 10-year history of isolated melanonychia striata of his dominant thumb. Surgical biopsy ruled out subungual melanoma but revealed foreign plant material causing chronic infectious melanonychia from multiple pathogens, including Pseudomonas aeruginosa, Escherichia coli, and Candida spp. After removal of the nail plate and thorough debridement, the melanonychial streak resolved completely at 12 months of follow-up.

CONCLUSION

Bacterial infection is a rarely reported cause of melanonychia, and in addition to surgical pathologic specimens, intraoperative fungal and bacterial cultures should always be obtained for accurate diagnosis of melanonychia striata.

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

A novel endophytic bacterial strain, designated GR-TSA-9^T, was isolated from surface-sterilized grape (Vitis vinifera L.). 16S rRNA gene sequence analyses showed that the isolate was grouped within the genus Brevundimonas, displaying the highest similarity with Brevundimonas lenta DS-18^T (97.9%) and Brevundimonas kwangchunensis KSL-102^T (97.8%) and less than 97.5% similarity with other members of Brevundimonas. The strain GR-TSA-9^T was a gram negative, rod shaped, facultatively anaerobic, catalase and oxidase positive, and motile bacterium. Its growth occurred at 10–37°C (optimally 25–30°C), at pH 7.0–8.0, and in NaCl 0–1% (optimally 0%). It contained ubiquinone-10 as a respiratory quinone, and the major cellular fatty acids (>10% of the total) were C_16:0 (14.2%) and summed feature 8 (C_18:1ω7c and/or C_18:1ω6c, 65.6%). The polar lipids present in the strain were phosphoglycolipids, phosphatidylglycerol, 1,2-di-O-acyl-3-O-[d-glucopyranosyl-(1→4)-α-d-glucopyranuronosyl]glycerol, and unidentified lipids (L1, L2, and L4). The strain had one 2,976,716bp circular chromosome with a G+C content of 66.4%. The digital DNA–DNA hybridization value between strain GR-TSA-9^T and B. lenta DS-18^T was 20.9%, while the average nucleotide identity value was 76.7%. In addition, the dDDH and ANI values to other members in this genus, whose genome sequences are available, are less than 21.1 and 77.6%. Genome annotation predicted the presence of some gene clusters related to tyrosine degradation and pyomelanin formation. Strain GR-TSA-9^T produced a brown melanin-like pigment in the presence of L-tyrosine-containing media. The highest pigment production (0.19g/L) was observed in tryptic soy broth with 1.0mg/ml L-tyrosine at 25°C for 6days of culture. Biophysical characterization by ultraviolet (UV)–visible spectroscopy, Fourier-transform infrared spectroscopy, and electrospray ionization mass spectrometry confirmed that the pigment was pyomelanin. Additionally, melanized GR-TSA-9^T cells could protect the cells against UVC exposure. The phylogenetic, genomic, phenotypic, and chemotaxonomic features indicated that strain GR-TSA-9^T represents a novel melanin-producing species of Brevundimonas. The type strain was GR-TSA-9^T (KCTC 82386^T=CGMCC 1.18820^T).

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

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.