Sulfadiazine uptake and effects in common hazel (Corylus avellana L.)

Soil contamination by antibiotics is a possible consequence of animal husbandry waste, sewage sludge, and reclaimed water spreading in agriculture. In this study, 1-year-old hazel plants (Corylus avellana L.) were grown in pots for 64 days in soil spiked with sulfadiazine (SDZ) in the range 0.01-100 mg kg(-1) soil. Leaf gas exchanges, fluorescence parameters and plant growth were measured regularly during the experiment, whereas plant biomass, sulfonamide concentrations in soil and plant tissues, and the quantitative variation of culturable bacterial endophytes in leaf petiole were analyzed at the end of the trial. During the experiment, photosynthesis and leaf transpiration as well as fluorescence parameters were progressively reduced by the antibiotic. Effects were more evident for leaf transpiration and for the highest SDZ spiking concentrations, whereas growth analyses did not reveal negative effects of the antibiotic. At the end of the trial, a high number of culturable endophytic bacteria in the leaf petiole of plants treated with 0.1 and 0.01 mg kg(-1) were observed, and SDZ was extractable from soil and plant roots for spiking concentrations ≥1 mg kg(-1). Inside plants, the antibiotic was mainly stored at the root level with bioconcentration factors increasing with the spiking dose, and the hydroxylated derivate 4-OH-SDZ was the only metabolite detected. Overall results show that 1-year-old hazel plants can contribute to the reduction of sulfonamide concentrations in the environment, however, sensitive reactions to SDZ can be expected at the highest contamination levels.

Microbiological features and bioactivity of a fermented manure product (preparation 500) used in biodynamic agriculture

The fermented manure derivative known as Preparation 500 is traditionally used as a field spray in biodynamic agriculture for maintaining and increasing soil fertility. This work aimed at characterizing the product from a microbiological standpoint and at assaying its bioactive properties. The approach involved molecular taxonomical characterization of the culturable microbial community; ARISA fingerprints of the total bacteria and fungal communities; chemical elemental macronutrient analysis via a combustion analyzer; activity assays for six key enzymes; bioassays for bacterial quorum sensing and chitolipooligosaccharide production; and plant hormonelike activity. The material was found to harbor a bacterial community of 2.38 × 10(8) CFU/g dw dominated by Grampositives with minor instances of Actinobacteria and Gammaproteobacteria. ARISA showed a coherence of bacterial assemblages in different preparation lots of the same year in spite of geographic origin. Enzymatic activities showed elevated values of beta-glucosidase, alkaline phosphatase, chitinase, and esterase. The preparation had no quorum sensing-detectable signal, and no rhizobial nod gene-inducing properties, but displayed a strong auxin-like effect on plants. Enzymatic analyses indicated a bioactive potential in the fertility and nutrient cycling contexts. The IAA activity and microbial degradation products qualify for a possible activity as soil biostimulants. Quantitative details and possible modes of action are discussed.

Evidence for calcium-mediated perception of plant symbiotic signals in aequorin-expressing Mesorhizobium loti

Background

During the interaction between rhizobia and leguminous plants the two partners engage in a molecular conversation that leads to reciprocal recognition and ensures the beginning of a successful symbiotic integration. In host plants, intracellular Ca²⁺ changes are an integral part of the signalling mechanism. In rhizobia it is not yet known whether Ca²⁺ can act as a transducer of symbiotic signals.

Results

A plasmid encoding the bioluminescent Ca²⁺ probe aequorin was introduced into Mesorhizobium loti USDA 3147^T strain to investigate whether a Ca²⁺ response is activated in rhizobia upon perception of plant root exudates. We find that M. loti cells respond to environmental and symbiotic cues through transient elevations in intracellular free Ca²⁺ concentration. Only root exudates from the homologous host Lotus japonicus induce Ca²⁺ signalling and downstream activation of nodulation genes. The extracellular Ca²⁺ chelator EGTA inhibits both transient intracellular Ca²⁺ increase and inducible nod gene expression, while not affecting the expression of other genes, either constitutively expressed or inducible.

Conclusion

These findings indicate a newly described early event in the molecular dialogue between plants and rhizobia and highlight the use of aequorin-expressing bacterial strains as a promising novel approach for research in legume symbiosis.

Construction of a Pseudomonas sp. derivative carrying the cry9Aa gene from Bacillus thuringiensis and a proposal for new standard criteria to assess entomocidal properties of bacteria

An isolate of Pseudomonas sp. (16S rDNA sequence 98% homologous to P. graminis and P. lutea) was isolated from the phyllosphere of black pine in northern Italy and used as a host for the gene encoding the Cry9Aa entomocidal toxin from Bacillus thuringiensis subsp. galleriae. An expression system featuring a synthetic highest-consensus promoter specifically tailored for the regulated induction of cloned genes over a broad range of Gram-negative bacteria was used to drive the production of the introduced toxin. The construct showed effective toxicity toward larvae of the greater wax moth (Galleria mellonella), which was also used as a model insect for establishing a number of newly proposed toxicity indices (LC50 cellular efficiency, toxin cellular efficiency, GMO efficiency, lethal cellular intake). These were devised in order to express toxicities of entomocidal bacteria in a standard fashion enabling the fine tuning of biocontrol treatments as well as the comparative evaluation of different reports.