ABSTRACT
The application of synthetic pesticides is one of the fastest acting tools at farmers' disposal to prevent and mitigate the threats posed by plant pests in agriculture. However, the effects of these above-ground applications of pesticides are known to be detrimental to some belowground, non-target soil biota. At present, the effects many pesticides have on key functional microbial groups associated with phosphate (P) solubilization in the soil are still largely unknown. The purpose of this study was to compare the effects of two herbicides, glyphosate, and paraquat, on phosphate solubilizing bacteria (PSB) with and without pH adjustment (after herbicide addition) since pH is a major indicator of P solubilization. In our assay, two PSB strains (Pantoea agglomerans and Serratia rubidaea) were chosen to assess their ability to solubilize tricalcium phosphate (TCP) by using the vanadate-molybdate method (to measure the amount of P solubilized) in the presence of glyphosate (5.4 g/L and 10.8 g/L) or paraquat (2 g/L and 4 g/L) separately. To assess the effect of PSB treated by the herbicides, a growth experiment using PSB inoculated wheat seedlings was performed under greenhouse conditions (25 °C, light 16 h/8 h dark). After four weeks, wheat above-ground growth parameters were measured. Our results showed that even under recommended doses of glyphosate (5.4 g/L) and paraquat (2 g/L), a decrease in P solubilization activity was observed in P. agglomerans and S. rubidaea. Whilst paraquat affected TCP solubilization more than glyphosate with and without pH adjustment, there was a significant decrease (p < 0.05) in TCP solubilization, up to 39% and 93% in the presence of glyphosate and paraquat, respectively, for S. rubidaea, and up to 45% and 95% in the presence of glyphosate and paraquat, respectively, for P. agglomerans. The effect of the herbicides on the PSB had the same results as in the greenhouse test on wheat seedling growth, confirming that these herbicides have both above and belowground negative effects, despite being used at recommended doses.
Subject(s)
Herbicides , Pantoea , Phosphates , Herbicides/toxicity , Soil , ParaquatABSTRACT
Biofertilizers are a key component of organic agriculture. Bacterial biofertilizers enhance plant growth through a variety of mechanisms, including soil compound mobilization and phosphate solubilizing bacteria (PSB), which convert insoluble phosphorus to plant-available forms. This specificity of PSB allows them to be used as biofertilizers in order to increase P availability, which is an immobile element in the soil. The objective of our study is to assess the capacity of PSB strains isolated from phosphate solid sludge to solubilize three forms of inorganic phosphates: tricalcium phosphate (Ca3(PO4)2), aluminum phosphate (AlPO4), and iron phosphate (FePO4), in order to select efficient solubilization strains and use them as biofertilizers in any type of soil, either acidic or calcareous soil. Nine strains were selected and they were evaluated for their ability to dissolve phosphate in the National Botanical Research Institute's Phosphate (NBRIP) medium with each form of phosphate (Ca3(PO4)2, AlPO4, and FePO4) as the sole source of phosphorus. The phosphate solubilizing activity was assessed by the vanadate-molybdate method. All the strains tested showed significantly (p ≤ 0.05) the ability to solubilize the three different forms of phosphates, with a variation between strains, and all strains solubilized Ca3(PO4)2 more than FePO4 and AlPO4.
ABSTRACT
The peculiar biotechnological applications of Oleispira spp. in the natural cleansing of oil-polluted marine systems stimulated the study of the phenotypic characteristics of the Oleispira antarctica RB-8(T) strain and modifications of these characteristics in relation to different growth conditions. Bacterial abundance, cell size and morphology variations (by image analysis) and hydrocarbon degradation (by gas chromatography with flame ionization detection, GC-FID) were analysed in different cultures of O. antarctica RB-8(T). The effects of six different hydrocarbon mixtures (diesel, engine oil, naval oil waste, bilge water, jet fuel and oil) used as a single carbon source combined with two different growth temperatures (4° and 15 °C) were analysed (for 22 days). The data obtained showed that the mean cell volume decreased with increasing experimental temperature. Three morphological bacterial shapes were identified: spirals, rods and cocci. Morphological transition from spiral to rod and coccoid shapes in relation to the different substrates (oil mixtures) and/or growth temperatures was observed, except for one experimental condition (naval oil waste) in which spiral bacteria were mostly dominant. Phenotypic traits and physiological status of hydrocarbon-degrading bacteria showed important modifications in relation to culture conditions. These findings suggest interesting potential for strain RB-8(T) for ecological and applicative purposes.
