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An improved Tn7-lux reporter for broad host range, chromosomally-integrated promoter fusions in Gram-negative bacteria.

ABSTRACT: An improved vector for chromosomally-integrated promoter-lux fusions is described. The modified vector was tested in parallel with the unmodified vector using the well-characterized Escherichia coli araBAD promoter in the Pseudomonas aeruginosa attTn7 site. The modified mini-Tn7 showed reduced background luminescence, and increased luminescence upon induction, giving >16-fold higher induction ratio.

SUBMITTER: Glassing A

PROVIDER: S-EPMC4624500 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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An improved Tn7-lux reporter for broad host range, chromosomally-integrated promoter fusions in Gram-negative bacteria.

Glassing Angela A Lewis Thomas A TA

Journal of microbiological methods 20150901

An improved vector for chromosomally-integrated promoter-lux fusions is described. The modified vector was tested in parallel with the unmodified vector using the well-characterized Escherichia coli araBAD promoter in the Pseudomonas aeruginosa attTn7 site. The modified mini-Tn7 showed reduced background luminescence, and increased luminescence upon induction, giving >16-fold higher induction ratio. ...[more]

PMID: 26341612

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Project description:BackgroundIn Gram-negative bacteria, type IV pili (TFP) have long been known to play important roles in such diverse biological phenomena as surface adhesion, motility, and DNA transfer, with significant consequences for pathogenicity. More recently it became apparent that Gram-positive bacteria also express type IV pili; however, little is known about the diversity and abundance of these structures in Gram-positives. Computational tools for automated identification of type IV pilins are not currently available.ResultsTo assess TFP diversity in Gram-positive bacteria and facilitate pilin identification, we compiled a comprehensive list of putative Gram-positive pilins encoded by operons containing highly conserved pilus biosynthetic genes (pilB, pilC). A surprisingly large number of species were found to contain multiple TFP operons (pil, com and/or tad). The N-terminal sequences of predicted pilins were exploited to develop PilFind, a rule-based algorithm for genome-wide identification of otherwise poorly conserved type IV pilins in any species, regardless of their association with TFP biosynthetic operons (http://signalfind.org). Using PilFind to scan 53 Gram-positive genomes (encoding >187,000 proteins), we identified 286 candidate pilins, including 214 in operons containing TFP biosynthetic genes (TBG+ operons). Although trained on Gram-positive pilins, PilFind identified 55 of 58 manually curated Gram-negative pilins in TBG+ operons, as well as 53 additional pilin candidates in operons lacking biosynthetic genes in ten species (>38,000 proteins), including 27 of 29 experimentally verified pilins. False positive rates appear to be low, as PilFind predicted only four pilin candidates in eleven bacterial species (>13,000 proteins) lacking TFP biosynthetic genes.ConclusionsWe have shown that Gram-positive bacteria contain a highly diverse set of type IV pili. PilFind can be an invaluable tool to study bacterial cellular processes known to involve type IV pilus-like structures. Its use in combination with other currently available computational tools should improve the accuracy of predicting the subcellular localization of bacterial proteins.

Project description:The development of new antibiotics is imperative to fight increasing mortality rates connected to infections caused by multidrug-resistant (MDR) bacteria. In this context, Gram-negative pathogens listed in the WHO priority list are particularly problematic. Darobactin is a ribosomally produced and post-translationally modified bicyclic heptapeptide antibiotic selectively killing Gram-negative bacteria by targeting the outer membrane protein BamA. The native darobactin A producer Photorhabdus khanii HGB1456 shows very limited production under laboratory cultivation conditions. Herein, we present the design and heterologous expression of a synthetically engineered darobactin biosynthetic gene cluster (BGC) in Escherichia coli to reach an average darobactin A production titre of 13.4 mg L-1. Rational design of darA variants, encoding the darobactin precursor peptide with altered core sequences, resulted in the production of 13 new 'non-natural' darobactin derivatives and 4 previously hypothetical natural darobactins. One of the non-natural compounds, darobactin 9, was more potent than darobactin A, and showed significantly improved activity especially against Pseudomonas aeruginosa (0.125 μg mL-1) and Acinetobacter baumannii (1-2 μg mL-1). Importantly, it also displayed superior activity against MDR clinical isolates of E. coli (1-2 μg mL-1) and Klebsiella pneumoniae (1-4 μg mL-1). Independent deletions of genes from the darobactin BGC showed that only darA and darE, encoding a radical forming S-adenosyl-l-methionine-dependent enzyme, are required for darobactin formation. Co-expression of two additional genes associated with the BGCs in hypothetical producer strains identified a proteolytic detoxification mechanism as a potential self-resistance strategy in native producers. Taken together, we describe a versatile heterologous darobactin platform allowing the production of unprecedented active derivatives in good yields, and we provide first experimental evidence for darobactin biosynthesis processes.

Dataset Information

An improved Tn7-lux reporter for broad host range, chromosomally-integrated promoter fusions in Gram-negative bacteria.

Publications

An improved Tn7-lux reporter for broad host range, chromosomally-integrated promoter fusions in Gram-negative bacteria.

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