Abstract
A violacein-producing bacterial strain was isolated and identified as a relative of Duganella violaceinigra YIM 31327 based upon phylogenetic analyses using the 16S rRNA, gyrB and vioA gene sequences and a fatty acid methyl ester (FAME) analysis. This new strain was designated D. violaceinigra str. NI28. Although these two strains appear related based upon these analyses, the new isolate was phenotypically different from the type strain as it grew 25% faster on nutrient media and produced 45-fold more violacein. When compared with several other violacein producing strains, including Janthinobacterium lividum, D. violaceinigra str. NI28 was the best violacein producer. For instance, the crude violacein yield with D. violaceinigra str. NI28 was 6.0 mg/OD at 24 hours, a value that was more than two-fold higher than all the other strains. Finally, the antibacterial activity of D. violaceinigra str. NI28 crude violacein was assayed using several multidrug resistant Staphylococcus aureus. Addition of 30 μM crude violacein led to a 96% loss in the initial S. aureus population while the minimum inhibitory concentration was 1.8 μM. Consequently, this novel isolate represents a phenotypic variant of D. violaceinigra capable of producing much greater quantities of crude violacein, an antibiotic effective against multidrug resistant S. aureus.
Highlights
A violacein-producing bacterial strain was isolated and identified as a relative of Duganella violaceinigra YIM 31327 based upon phylogenetic analyses using the 16S rRNA, gyrB and vioA gene sequences and a fatty acid methyl ester (FAME) analysis
When the crude violacein extracted from our new isolate was compared with a commercial preparation of crude violacein from Janthinobacterium lividum (Sigma-Aldrich, USA), they were basically indistinguishable from each other
Identification of this strain was performed using the sequences obtained from three gene loci (16S rRNA, gyrB and vioA), with each confirming that it was closely related to Duganella violaceinigra YIM 31327 (Figs 2 and 3)
Summary
A violacein-producing bacterial strain was isolated and identified as a relative of Duganella violaceinigra YIM 31327 based upon phylogenetic analyses using the 16S rRNA, gyrB and vioA gene sequences and a fatty acid methyl ester (FAME) analysis. A recent study demonstrated that violacein works synergistically with other antibiotics, leading to significantly lower minimum inhibitory concentrations for S. aureus, Klebsiella pneumonia and Pseudomonas aeruginosa[6] All three of these strains are included in the ESKAPE pathogen grouping, a list of multidrug resistant bacteria that are becoming more prominent within healthcare environments and nosocomial infections[8,9]. NI28, obtained from a temperate forest soil sample taken near Ulsan, South Korea This strain produces violacein at much higher rate and levels than the type strain D. violaceinigra YIM 3132724,27
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