Impact of Delftia tsuruhatensis and Achromobacter xylosoxidans on Escherichia coli dual-species biofilms treated with antibiotic agents.

Recently it was demonstrated that for urinary tract infections species with a lower or unproven pathogenic potential, such as Delftia tsuruhatensis and Achromobacter xylosoxidans, might interact with conventional pathogenic agents such as Escherichia coli. Here, single- and dual-species biofilms of these microorganisms were characterized in terms of microbial composition over time, the average fitness of E. coli, the spatial organization and the biofilm antimicrobial profile. The results revealed a positive impact of these species on the fitness of E. coli and a greater tolerance to the antibiotic agents. In dual-species biofilms exposed to antibiotics, E. coli was able to dominate the microbial consortia in spite of being the most sensitive strain. This is the first study demonstrating the protective effect of less common species over E. coli under adverse conditions imposed by the use of antibiotic agents.

Characterization and Genomic Analysis of Quinolone-Resistant Delftia sp. 670 Isolated from a Patient Who Died from Severe Pneumonia.

Antibiotic-resistant opportunistic pathogens have become a serious concern in recent decades, as they are increasingly responsible for hospital-acquired infections. Here, we describe quinolone-resistant Delftia sp. strain 670, isolated from the sputum of a patient who died from severe pulmonary infection. The draft genome sequence of this strain was obtained by whole-genome shotgun sequencing, and was subjected to comparative genome analysis. Genome analysis revealed that one critical mutation (Ser83Ile in gyrA) might play a decisive role in quinolone resistance. The genome of Delftia sp. strain 670 contains both type II and type VI secretion systems, which were predicted to contribute to the virulence of the strain. Phylogenetic analysis, assimilation tests, and comparative genome analysis indicated that strain 670 differed from the four known Delftia species, suggesting this strain could represent a novel species. Although the study could not determine the strain 670 as the pathogen led to mortality, our findings also presented the pathogenic potential of Delftia species, and the increasing severity of antibiotic resistance among emerging opportunistic pathogens. The whole genome sequencing and comparative analysis improved our understanding of genome evolution in the genus Delftia, and provides the foundation for further study on drug resistance and virulence of Delftia strains.

Bacterial swimming, swarming and chemotactic response to heavy metal presence: which could be the influence on wastewater biotreatment efficiency?

Fixed-bed reactors are usually designed for wastewater biotreatments, where the biofilm establishment and maintenance play the most important roles. Biofilm development strictly relies on different types of bacterial motility: swimming, swarming, and chemotaxis, which can be altered by the microenvironment conditions. The aim of this work is to do an integrated study on the effects of Cu(II), Cd(II), Zn(II) and Cr(VI) on swimming, swarming and chemotaxis of Pseudomonas veronii 2E, Delftia acidovorans AR and Ralstonia taiwanensis M2 to improve biofilm development and maintenance for metal loaded wastewater biotreatment in fixed-bed bioreactors. Swimming, swarming and chemotactic response evaluation experiments were carried out at different metal concentrations. P. veronii 2E motility was not affected by metal presence, being this strain optimal for fixed-bed reactors. D. acidovorans AR swarming was inhibited by Cd and Zn. Although R. taiwanensis M2 showed high resistance to Cu, Cd, Cr and Zn, motility was definitively altered, so further studies on R. taiwanensis M2 resistance mechanisms would be particularly interesting.

Delftia sp. JD2: a potential Cr(VI)-reducing agent with plant growth-promoting activity.

A chromium (Cr)-resistant bacterium isolated from soil containing 6,000 mg/kg of Cr was identified based on 16S rRNA gene sequence analysis as Delftia, and designated as JD2. Growth of JD2 was accompanied with reduction of Cr(VI) to Cr(III) in liquid medium initially containing 100 mg/L Cr(VI), the maximum concentration allowing growth. JD2 showed NADH/NADPH-dependent reductase activity associated with the soluble fraction of cells. The results suggest that JD2 might be a good candidate for the treatment of highly Cr(VI)-contaminated water and/or industrial effluents. The isolate produced indole-3-acetic acid in the presence and absence of Cr(VI) and showed free-living nitrogen-fixing activity possibly attributable to a V-nitrogenase. JD2 did not counteract the harmful effect of Cr(VI) during leguminous plant growth and nodulation by rhizobial strains but functioned as a "helper" bacterium to enhance the performance of rhizobial inoculant strains during inoculation of alfalfa and clover (used as model plants to study plant growth-promoting activity) in the absence of Cr(VI).

Structure of haloacetate-catabolic IncP-1beta plasmid pUO1 and genetic mobility of its residing haloacetate-catabolic transposon.

The self-transmissible plasmid pUO1 from Delftia acidovorans strain B carries two haloacetate-catabolic transposons, TnHad1 and TnHad2, and the mer genes for resistance to mercury. The complete 67,066-bp sequence of pUO1 revealed that the mer genes were also carried by two Tn402/Tn5053-like transposons, Tn4671 and Tn4672, and that the pUO1 backbone regions shared 99% identity to those of the archetype IncP-1beta plasmid R751. Comparison of pUO1 with three other IncP-1beta plasmids illustrated the importance of transposon insertion in the diversity and evolution of this group of plasmids. Mutational analysis of the four outermost residues in the inverted repeats (IRs) of TnHad2, a Tn21-related transposon, revealed a crucial role of the second residue of its IRs in transposition.