A genomic and transcriptomic approach to investigate the blue pigment phenotype in Pseudomonas fluorescens

Abstract

a b s t r a c t a r t i c l e i n f oPseudomonas fluorescens is a well-known food spoiler, able to cause serious economic losses in the food industry due to its ability to produce many extracellular, and often thermostable, compounds. The most outstanding spoilage events involving P. fluorescens were blue discoloration of several food stuffs, mainly dairy products. The bacteria involved in such high-profile cases have been identified as belonging to a clearly distinct phylogenetic cluster of the P. fluorescens group. Although the blue pigment has recently been investigated in several studies, the biosynthetic pathway leading to the pigment formation, as well as its chemical nature, remain challenging and unsolved points. In the present paper, genomic and transcriptomic data of 4 P. fluorescens strains (2 blue-pigmenting strains and 2 non-pigmenting strains) were analyzed to evaluate the presence and the expression of blue strain-specific genes. In particular, the pangenome analysis showed the presence in the blue-pigmenting strains of two copies of genes involved in the tryptophan biosynthesis pathway (including trpABCDF). The global expression profiling of bluepigmenting strains versus non-pigmenting strains showed a general up-regulation of genes involved in iron uptake and a down-regulation of genes involved in primary metabolism. Chromogenic reaction of the bluepigmenting bacterial cells with Kovac's reagent indicated an indole-derivative as the precursor of the blue pigment. Finally, solubility tests and MALDI-TOF mass spectrometry analysis of the isolated pigment suggested that its molecular structure is very probably a hydrophobic indigo analog.

Transcriptomic analysis of the response of Pseudomonas fluorescens to epigallocatechin gallate by RNA-seq

“…Pseudomonas fluorescens is a common gram-negative spoilage bacterium that is widely found in food matrices, such as ready-prepared fresh vegetables [29], raw fish (especially sushi or sashimi) [30], meat and dairy products [31]. Due to its extreme adaptability, versatility and ability to replicate at refrigeration temperatures, long periods of shelf life can easily lead to increased P .…”

H2O2 Tolerance in Pseudomonas Fluorescens: Synergy between Pyoverdine‐Iron(III) Complex and a Blue Extracellular Product Revealed by a Nanotechnology‐Based Electrochemical Approach

“…[3] This result suggests that the biosynthesis of a blue pigment can be at the core of the observed oxidative stress tolerance, as previously proposed for Erwinia chrysanthemi. [4] The chemical nature of the pigment behind the blue discoloration has spurred an intense debate over the last years, [3,5] hence its identification remains an open task. Nevertheless, the molecule conferring the blue color is part of the complex extracellular heritage of P. fluorescens.…”

“…More recently, blue coloration in P. fluorescens was attributed to the presence of an indigo derivative (Figure 1 a). [5] For these reasons, indigo was used in the present study as reference compound (Figure 1 a). Herein, electrochemistry, was used in combination with the advantages offered by novel biomolecule-nanomaterial hybrids.…”

“…[1] Some strains of P. fluorescens produce a characteristic blue pigment, [2] and, recently, we demonstrated that, conversely to white mutants, blue colored P. fluorescens strains present high resistance to oxidative stress induced by hydrogen peroxide. [4] The chemical nature of the pigment behind the blue discoloration has spurred an intense debate over the last years, [3,5] hence its identification remains an open task. [4] The chemical nature of the pigment behind the blue discoloration has spurred an intense debate over the last years, [3,5] hence its identification remains an open task.…”

“…[8] Moreover, Caputo and colleagues suggested the presence of an uncolored parental compound of indigoidine (leuco-indigoidine) in P. fluorescens, [9] which could be involved in the blue pigment production. [5] For these reasons, indigo was used in the present study as reference compound (Figure 1 a). [5] For these reasons, indigo was used in the present study as reference compound (Figure 1 a).…”