A novel, green, low-cost chitosan-starch hydrogel as potential delivery system for plant growth-promoting bacteria.

The study examines the use of macrobeads for the controlled-release of bacteria. Macrobeads were prepared by an easy dripping-technique using 20/80 wt/wt chitosan-starch blends and sodium tripolyphosphate as cross-linking agent. The resulting polymeric matrix was examined by SEM, XRD, TGA, and solid-RMN. The swelling-equilibrium, thermal behaviour, crystallinity, and size of macrobeads were affected by the autoclave-sterilization. The diameter of the sterilized xerogel was c.a. 1.6 mm. The results suggested that ionotropic-gelation and neutralization were the mechanisms underlying hydrogel formation. Plant growth-promoting bacteria (PGPB) were loaded into macrobeads separately or co-inoculated. Bacteria loaded macrobeads were dried and stored. Bacteria survived at least 12 months in orders of 109 CFU of A. brasilense/g and 108 CFU of P. fluorescens/g. Bacterial release in sterile saline solution tended to a super Case-II transport mechanism. Polymeric-matrix release efficiently both PGPB in natural soils, which uncovers their potential for the formulation of novel and improved biofertilizers.

Identification of sulfonylurea biodegradation pathways enabled by a novel nicosulfuron-transforming strain Pseudomonas fluorescens SG-1: Toxicity assessment and effect of formulation.

Nicosulfuron is a selective herbicide belonging to the sulfonylurea family, commonly used on maize culture. A bacterial strain SG-1 was isolated from an agricultural soil previously treated with nicosulfuron. This strain was identified as Pseudomonas fluorescens and is able to quantitatively dissipate 77.5% of nicosulfuron (1mM) at 28°C in the presence of glucose within the first day of incubation. Four metabolites were identified among which ASDM (2-(aminosulfonyl)-N,N-dimethyl-3-pyridinecarboxamide) and ADMP (2-amino-4,6-dimethoxypyrimidine) in substantial proportions, corresponding to the hydrolytic sulfonylurea cleavage. Two-phase dissipation kinetics of nicosulfuron by SG-1 were observed at the highest concentrations tested (0.5 and 1mM) due to biosorption. The extend and rate of formulated nicosulfuron transformation were considerably reduced compared to those with the pure active ingredient (appearance of a lag phase, 30% dissipation after 10days of incubation instead of 100% with the pure herbicide) but the same metabolites were observed. The toxicity of metabolites (standardized Microtox® test) showed a 20-fold higher toxicity of ADMP than nicosulfuron. P. fluorescens strain SG-1 was also able to biotransform two other sulfonylureas (metsulfuron-methyl and tribenuron-methyl) with various novel pathways. These results provide new tools for a comprehensive picture of the sulfonylurea environmental fate and toxicity of nicosulfuron in the environment.

No apparent costs for facultative antibiotic production by the soil bacterium Pseudomonas fluorescens Pf0-1.

BACKGROUND: Many soil-inhabiting bacteria are known to produce secondary metabolites that can suppress microorganisms competing for the same resources. The production of antimicrobial compounds is expected to incur fitness costs for the producing bacteria. Such costs form the basis for models on the co-existence of antibiotic-producing and non-antibiotic producing strains. However, so far studies quantifying the costs of antibiotic production by bacteria are scarce. The current study reports on possible costs, for antibiotic production by Pseudomonas fluorescens Pf0-1, a soil bacterium that is induced to produce a broad-spectrum antibiotic when it is confronted with non-related bacterial competitors or supernatants of their cultures. METHODOLOGY AND PRINCIPAL FINDINGS: We measured the possible cost of antibiotic production for Pseudomonas fluorescens Pf0-1 by monitoring changes in growth rate with and without induction of antibiotic production by supernatant of a bacterial competitor, namely Pedobacter sp.. Experiments were performed in liquid as well as on semi-solid media under nutrient-limited conditions that are expected to most clearly reveal fitness costs. Our results did not reveal any significant costs for production of antibiotics by Pseudomonas fluorescens Pf0-1. Comparison of growth rates of the antibiotic-producing wild-type cells with those of non-antibiotic producing mutants did not reveal costs of antibiotic production either. SIGNIFICANCE: Based on our findings we propose that the facultative production of antibiotics might not be selected to mitigate metabolic costs, but instead might be advantageous because it limits the risk of competitors evolving resistance, or even the risk of competitors feeding on the compounds produced.

Assessment of toxicity of the untreated and treated olive mill wastewaters and soil irrigated by using microbiotests.

Hazard assessments based on two measures of toxicity were conducted for the untreated olive mill wastewaters (U), untreated olive mill wastewaters organic extract (UOE), treated olive mill wastewaters (T), treated olive mill wastewaters organic extract (TOE) and extracts of soils ferti-irrigated with untreated (SU) and with treated olive mill wastewaters (ST). The measures of toxicity were achieved by the determination of the bioluminescence inhibition percent (I(B)%) of Vibrio fischeri and by the growth inhibition (GI) of Bacillus megaterium, Pseudomonas fluorescens and Escherichia coli. A bioluminescence inhibition of V. fischeri of 100%, 100%, 65%, 47%, 46% and 30% were obtained with U, UOE, T, TOE, SU and ST respectively. Indeed, even diluted 24 times, a significant bioluminescence inhibition of 96% was obtained by U. However, only 30% bioluminescence inhibition was obtained by 24 times diluted T. Whereas, 24 times diluted, SU and ST did not show a bioluminescence inhibition (3% and 1%, respectively). The GI of B. megaterium, P. fluorescens and E. coli were, respectively, 93%, 72% and 100% by U; 100%, 80% and 100% by UOE; 70%, 60% and 89% by T; 63%, 54% and 68% by TOE; 39%, 27% and 43% by SU and 23%, 0% and 34% by ST. The incubation of U or T in the soil during four months reduced their toxicity by 54% and 35%, respectively. As it was expected, the most resistant bacterium to OMW toxicity is P. fluorescens then B. megaterium and E. coli. V. fischeri remained the most sensitive strain to the toxicity of this sewage what proves again its utilisation as standard of measure of the toxicity.

An ecotoxicity assessment of contaminated forest soils from the Kola Peninsula.

Point source copper and nickel contamination emanating from smelters of the Kola Peninsula, NW Russia, has been observed since the mid-1960s. Previous studies have concentrated on the spatial distribution of heavy metals and their effects on forest ecology and indigenous mammals and birds. Soil is perceived as the major repository for the metal pollutants but there is a need to link the soil concentration of pollutants on the Kola Peninsula with biological parameters. Many standard methods currently used in soil ecotoxicology are developed and refined with artificial amendments and rarely modified for use in historically contaminated environments. In this study, forest soils were sampled along a 34 km transect from the smelter and analysed both chemically and with a range of ecologically relevant biological tests. Soil respiration, total nematode count, microbial heterotrophic numbers and minimal inhibitory concentrations to copper and nickel were carried out on bulk soil. The soil pore water was tested with bacterial and fungal bioluminescence-based biosensors. The heterotrophic numbers and their inhibitory concentration showed strong correlation with heavy metal concentrations while decreasing biosensor luminescence was related to increasing copper concentrations present in the pore waters. Overall, there were considerable impacts on some microbial parameters but other measures including respiration and nematode populations were insensitive to pollutant levels. While chemical analysis of heavy metals proved essential in defining the extent of contamination, environmentally relevant ecotoxicological tests complemented these data by demonstrating pollutant impact. Ecotoxicological approaches that study both the bulk soil and pore water may represent the key to understanding the fate of heavy metal in soils.

Assessment of bioavailable arsenic and copper in soils and sediments from the Antofagasta region of northern Chile.

Copper levels of nearly 500 mg l(-1) were measured in aqueous extracts of soil and sediment samples from the lowlands of Antofagasta. Arsenic levels of up to 183 mg l(-1) were found in river sediments, and 27.5 mg l(-1) arsenic was found at the location of a dam where potable water is extracted. This indicates that the arsenic contamination of water supplies reported recently for the pre-Andes may be a widespread problem throughout the region. Copper contamination from smelting activities also provides cause for concern as elevated levels were found in aqueous extracts of soil up to 20 km away from a smelter. This study went beyond traditional chemical analysis by assessing the potential benefits of using microbial biosensors as an alternative to determination of chemical speciation, to provide an environmentally relevant interpretation of soil/sediment residue levels. This approach is simple to use and enables a rapid, low cost assessment of pollutant bioavailability. It may, therefore, be of use for further investigations in the region and beyond.

Lux-biosensor assessment of pH effects on microbial sorption and toxicity of chlorophenols.

Lux-marked bacterial biosensors and a commercial toxicity testing bacterial strain (Microtox) were exposed to 2,4-dichlorophenol (DCP) and the light output response measured. Increasing DCP concentrations caused a decrease in light output in all three biosensors with an order of sensitivity (in terms of luminescence decrease over the DCP concentration range) of Pseudomonas fluorescens < Escherichia coli < Microtox. Adsorption of DCP to E. coli was measured using uniformly ring labelled [14C]DCP and found to be very rapid. The effect of pH on toxicity and adsorption was also investigated. Low pH values increased the amount of DCP adsorbed to the cell and increased the toxicity of DCP.

Toxicity assessment of xenobiotic contaminated groundwater using lux modified Pseudomonas fluorescens.

A bacterial bioassay, suitable for rapid screening to assess the relative toxicity of xenobiotic contaminated groundwater has been developed. The quantitative bioassay utilizes a decline in luminescence of the lux marked soil bacterium Pseudomonas fluorescens on exposure to contaminated groundwaters from which effective concentration (EC) values can be assessed and compared. P. fluorescens was most sensitive to semivolatile organics in groundwaters but there was no correlation between EC value and chemical content. The sensitivity and reproducibility of the P. fluorescens bioassay was compared with that of Microtox and results showed that mean EC50 values for diluted ground water replicate samples were 20% and 18% respectively. This suggested that the P. fluorescens bioassay was as applicable to groundwater screening as the widely used Microtox bioassay.

[Assessment of the degree of electrochemical treatment of sewage using biotesting]. / Otsenka stepeni élektrokhimicheskoi obrabotki stochnykh vod s pomoshch'iu biotestirovaniia.

Studies were conducted on estimation of the toxicity levels in various oxygen-containing chlorine compounds formed during electrochemical treatment of sewage by using a culture isolated from activated sludge purifying antibiotic production waste. It was shown that the products formed during electrocatalytic treatment of solutions (concentration of NaCl 1.5-5 g/l, pH 2.0-12.0, volumetric current density up to 10 A/l) were not toxic and stimulated the growth of P. fluorescens.