Lemna minor tolerance to metal-working fluid residues: implications for rhizoremediation.

For the first time in the literature, duckweed (Lemna minor) tolerance (alone or in combination with a consortium of bacteria) to spent metal-working fluid (MWF) was assessed, together with its capacity to reduce the chemical oxygen demand (COD) of this residue. In a preliminary study, L. minor response to pre-treated MWF residue (ptMWF) and vacuum-distilled MWF water (MWFw) was tested. Plants were able to grow in both residues at different COD levels tested (up to 2300 mg·l(-1) ), showing few toxicity symptoms (mainly growth inhibition). Plant response to MWFw was more regular and dose responsive than when exposed to ptMWF. Moreover, COD reduction was less significant in ptMWF. Thus, based on these preliminary results, a second study was conducted using MWFw to test the effectiveness of inoculation with a bacterial consortium isolated from a membrane bioreactor fed with the same residue. After 5 days of exposure, COD in solutions containing inoculated plants was significantly lower than in non-inoculated ones. Moreover, inoculation reduced ß+γ-tocopherol levels in MWFw-exposed plants, suggesting pollutant imposed stress was reduced. We therefore conclude from that L. minor is highly tolerant to spent MWF residues and that this species can be very useful, together with the appropriate bacterial consortium, in reducing COD of this residue under local legislation limits and thus minimise its potential environmental impact. Interestingly, the lipophilic antioxidant tocopherol (especially the sum of ß+γ isomers) proved to be an effective plant biomarker of pollution.

Bacterial siderophores efficiently provide iron to iron-starved tomato plants in hydroponics culture.

Iron is one of the essential elements for a proper plant development. Providing plants with an accessible form of iron is crucial when it is scant or unavailable in soils. Chemical chelates are the only current alternative and are highly stable in soils, therefore, posing a threat to drinking water. The aim of this investigation was to quantify siderophores produced by two bacterial strains and to determine if these bacterial siderophores would palliate chlorotic symptoms of iron-starved tomato plants. For this purpose, siderophore production in MM9 medium by two selected bacterial strains was quantified, and the best was used for biological assay. Bacterial culture media free of bacteria (S) and with bacterial cells (BS), both supplemented with Fe were delivered to 12-week-old plants grown under iron starvation in hydroponic conditions; controls with full Hoagland solution, iron-free Hoagland solution and water were also conducted. Treatments were applied twice along the experiment, with a week in between. At harvest, plant yield, chlorophyll content and nutritional status in leaves were measured. Both the bacterial siderophore treatments significantly increased plant yield, chlorophyll and iron content over the positive controls with full Hoagland solution, indicating that siderophores are effective in providing Fe to the plant, either with or without the presence of bacteria. In summary, siderophores from strain Chryseobacterium C138 are effective in supplying Fe to iron-starved tomato plants by the roots, either with or without the presence of bacteria. Based on the amount of siderophores produced, an effective and economically feasible organic Fe chelator could be developed.

Screening for putative PGPR to improve establishment of the symbiosis Lactarius deliciosus-Pinus sp.

A screening for plant growth promoting rhizobacteria (PGPR) was carried out in the mycorrhizosphere of wild populations of Pinus pinea and P. pinaster, and in the mycosphere of associated Lactarius deliciosus. A total of 720 bacteria were isolated, purified, and grouped by morphological criteria. Fifty percent of the isolates were selected and tested for aminocyclopropanecarboxylic acid (ACC) degradation, auxin and siderophore production, and phosphate solubilization. Thirty eight percent of the isolates showed at least one of the evaluated activities. Nutrient-related traits were associated with P. pinaster, whereas hormone production traits predominated in P. pinea. These activities were found mostly in Gram positive isolates. After PCR-RAPDs (random amplified polymorphic DNA) analysis, 10 groups appeared with 85% similiarity when considering all isolates, indicating the low diversity in the system. One strain of each group was identified by 16S rDNA sequencing. Our results suggest that P. pinaster selects for mycorrhizosphere bacteria that mobilize nutrients, whereas P. pinea selects for bacteria that have the capacity to increase root growth via production of plant growth regulators.

Uptake and distribution of zinc, cadmium, lead and copper in Brassica napus var. oleífera and Helianthus annus grown in contaminated soils.

Brassica napus var. oleifera and Helianthus annus were grown in artificially contaminated soils. Accumulation and translocation of the environmental pollutants zinc, cadmium, lead, and copper, was evaluated in different portions of the plants at two harvesting times. The distribution into the plants of these metal ions, as well as their capacity for contaminant phytoextraction and accumulation was assessed. For this purpose, an analytical method utilizing focused ultrasound employed for extraction and stripping voltammetry for measurement has been optimized and validated for the simultaneous measurement of Zn, Cd, Pb, and Cu in plant extracts.

Low molecular weight organic acids and fatty acids in root exudates of two Lupinus cultivars at flowering and fruiting stages.

Low molecular weight organic acids (LOAs) and fatty acids in root exudates of two lupin cultivars, Lupinus albus cv. Multolupa and L. luteus cv. Tremosilla, were determined at flowering and fruiting stages. LOAs were analysed by capillary electrophoresis. Acetic and citric acids were the most abundant, especially the latter in L. luteus at the flowering stage (5922.79 micrograms/g dry root). The significant decrease in acid content of both cultivars from flowering to fruiting stages was also striking. The highest levels of acetic acid were detected in L. luteus at fruiting stage (1542.03 micrograms/g dry root). The significant citrate production in L. luteus could be related to the low phosphorus concentration in the studied soils but not to proteoid roots, which were detected only in L. albus. The source of the LOAs detected in these exudates is also discussed, since they may be produced either by the plant or by the associated rhizobacteria. The profile of phospholipid fatty acids was determined by high-resolution GC. A high level of 18:2 omega 6 (a fatty-acid specific to fungi) was found in exudates of L. luteus (a mycorrhizal plant) in contrast to L. albus (a non-mycorrhizal plant).

Effects of Inoculation with PGPR Bacillus and Pisolithus tinctorius on Pinus pinea L. Growth, Bacterial rhizosphere Colonization, and Mycorrhizal Infection.

The effect of co-inoculation with Pisolithus tinctorius and a PGPR belonging to the genus Bacillus (Bacillus licheniformis CECT 5106 and Bacillus pumilus CECT 5105) in enhancing growth of Pinus pinea plants and the changes that occurred in rhizosphere microbial communities and the degree of mycorrhization were evaluated. Both bacterial strains of Bacillus promote the growth of Pinus pinea seedlings, but this biological effect does not imply a synergic effect with mycorrhizal infection. However, the positive response to mycorrhiza in a longer-term experiment it could be expected. The introduction of both inocula causes an alteration in the microbial rhizosphere composition, despite the low levels of inocula that were found at the end of the assay.