2,6-Dichlorobenzamide (BAM) herbicide mineralisation by Aminobacter sp. MSH1 during starvation depends on a subpopulation of intact cells maintaining vital membrane functions.

Mineralisation capability was studied in the 2,6-dichlorobenzamide (BAM)-degrading Aminobacter sp. MSH1 under growth-arrested conditions. Cells were starved in mineral salts (MS) solution or groundwater before (14)C-labelled BAM (0.1mM) was added. Cell physiology was monitored with a panel of vitality stains combined with flow cytometry to differentiate intact, depolarised and dead cells. Cells starved for up to 3 weeks in MS solution showed immediate growth-linked mineralisation after BAM amendment while a lag-phase was seen after 8 weeks of starvation. In contrast, cells amended with BAM in natural groundwater showed BAM mineralisation but no growth. The cell-specific mineralisation rate was always comparable (10(-16)molCintact cell(-1)day(-1)) independent of media, growth, or starvation period after BAM amendment; lower rates were only observed as BAM concentration decreased. MSH1 seems useful for bioremediation and should be optimised to maintain an intact cell subpopulation as this seems to be the key parameter for successful mineralisation.

TOL plasmid carriage enhances biofilm formation and increases extracellular DNA content in Pseudomonas putida KT2440.

Adherent growth of Pseudomonas putida KT2440 with and without the TOL plasmid (pWWO) at the solid-liquid and air-liquid interface was examined. We compared biofilm formation on glass in flow cells, and assayed pellicle (air-liquid interface biofilm) formation in stagnant liquid cultures by confocal laser scanning microscopy. The TOL-carrying strains formed pellicles and thick biofilms, whereas the same strains without the plasmid displayed little adherent growth. Microscopy using fluorescent nucleic acid-specific stains revealed differences in the production of extracellular polymeric substances: TOL carriage leads to more extracellular DNA (eDNA) in pellicles and biofilms. Pellicles were dissolved by DNase I treatment. Enhanced cell lysis due to plasmid carriage was ruled out as the mechanism for eDNA release. We report, for the first time, that carriage of a conjugative plasmid leads to increased biofilm formation by production of eDNA.

Increased pollution-induced bacterial community tolerance to sulfadiazine in soil hotspots amended with artificial root exudates.

Sulfadiazine (SDZ) residues constitute an important pollutant in soils that may increase environmental reservoirs of antibiotic resistance. Our primary aim was to compare the development of pollution-induced community tolerance (PICT) to SDZ concentration levels in bulk soil and nutrient amended soil hotspots. Agricultural soil microcosms were amended with different concentrations of SDZ with or without weekly additions of artificial root exudates corresponding to realistic rhizodeposition rates. Bacterial community tolerance to SDZ residues, as determined by the [3H]leucine incorporation technique, increased progressively with elevated SDZ exposure, and was significantly increased in soil hotspots (LOEC of 1microg kg(-1)). An alternative PICT approach based on single-cell esterase probing by flow cytometry failed to demonstrate SDZ impacts. Bacterial growth rates ([3H]leucine incorporation) were significantly reduced in both bulk soil and hotspots 24 h after amendment with environmentally relevant concentrations of SDZ, while soil respiration remained unaffected even at 100 microg SDZ g(-1). Our study for the first time demonstrates a drastically increased PICT response of a soil bacterial community due to increased carbon substrate amendment per se. Hence, hotspot soil environments such as rhizosphere and manure-soil interfaces may comprise key sites for proliferation of bacteria that are resistant or tolerant to antibiotics.