Borbála Biró

Synergistic and antagonistic effects of arbuscular mycorrhizal fungi and Azospirillum and Rhizobium nitrogen-fixers on the photosynthetic activity of alfalfa, probed by the polyphasic chlorophyll a fluorescence transient O-J-I-P☆

The synergistic and antagonistic effects of arbuscular mycorrhizal fungi (AMF) and Azospirillum and Rhizobium nitrogen-fixers on the photosynthetic activity of alfalfa (Medicago sativa L.) were studied by means of the polyphasic chlorophyll a (Chl a) fluorescence transient O-J-I-P. The effects were evaluated on alfalfa plants grown in: (a) loamy chernozem control soil including the original rhizosphere community (bacteria+AMF); (b) gamma-sterilised soil (no microbes); (c) bacterial re-inoculated AMF-free soil (only bacteria). In these substrates the plants were inoculated with AMF (Glomus fasciculatum M107), with and without co-inoculation with the associative (Azospirillum brasilense Km5) and/or the symbiotic (Rhizobium meliloti Lu41+S5/7+K4/1) nitrogen-fixing bacteria. The Chl a fluorescence transients were recorded in vivo and analysed according to the JIP-test leading to the calculation of a constellation of parameters quantifying the photosystem II (PSII) behaviour. The beneficial effect of AMF is clearly revealed by the observed enhancement of the electron transport activity per leaf area. Based on the same criterion, an antagonism by both bacteria was detected. The antagonistic effect of Azospirillum was more pronounced than that of Rhizobium, though not strong enough to fully counter-balance for the beneficial effect of AMF. However, in the case of co-inoculation with both diazotrophs and AMF the electron transport activity was found to be only slightly lower than in the case of single inoculation by AMF, indicating that, in the presence of each other, the diazotrophs are no longer antagonistic to AMF. It was further clarified that these antagonistic effects are the net result of different synergistic and antagonistic effects, as follows: (a) Concerning the electron transport activity per absorption, Rhizobium has a synergistic effect on AMF’s beneficial role, which is even more pronounced in the case of the tripartite co-inoculation, though Azospirillum in the absence of Rhizobium is antagonistic to AMF. (b) Concerning absorption per leaf, the beneficial influence of AMF is almost fully counterbalanced by co-inoculation with each of the diazotrophs or by both of them. The results demonstrate that the different combinations of inoculations and/or soils can be well distinguished by means of the JIP-test parameters and they thus suggest that the test can be used to screen, through the PSII behaviour of the plants, the effect of the microbial activity in the field. Two-dimensional rankings of the several soil/microbe combinations, in respect to the values of different energy fluxes, are shown to provide mappings that can be useful for the comparison of whole ecosystems or of individuals within an ecosystem.

Interrelations between Azospirillum and Rhizobium nitrogen-fixers and arbuscular mycorrhizal fungi in the rhizosphere of alfalfa in sterile, AMF-free or normal soil conditions

Abstract Co-inoculations of the alfalfa (Medicago sativa L.) plants with the associative- and/or the obligate nitrogen-fixing bacteria (Azospirillum brasilense, S; Rhizobium meliloti, R) and/or the vesicular arbuscular mycorrhiza fungus (Glomus fasciculatum, M) were evaluated in a pot experiment under controlled conditions. The effect of these beneficial microbes, as single- (M, R, S), dual- (MR, MS) or multilevel (MRS) inoculation-treatments were assessed in a calcareous loamy chernozem soil, originating from a grass-type natural ecosystem. A range of substrates were used to separate the influence of the indigenous microbes: C, untreated original soil (i.e. including all of the usual microflora); G, gamma-sterilised soil (no competitive microbes); GB, sterile soil (re-suspension of a mycorrhiza-free soil extract). The weight of the host, nodule-number, macro- and microelement contents and the colonisation by the inoculated bacterial and fungal microsymbionts were recorded. In the gamma-sterilised substrate all of the mono- (M), dual- (MR, MS) or multilevel (MRS) co-inoculations with the selected, Glomus fasciculatum M 107 strain were effective in improving plant growth, nutrient-uptake and abundance of the microsymbionts in the rhizosphere of alfalfa. In contrast a competition from the indigenous microflora in the non-sterilised soil, greatly reduced the functioning of the applied mycorrhizal inoculum. Although the associative Azospirillum bacteria (MS) slightly reduced effects relative to single mycorrhizal inoculation (M), the multilevel treatments, with both of the diazotrophs (MRS), showed a further enhancement (a synergistic effect) for almost all of the tested parameters and substrates. The functional compatibility of the obligate- and associative diazotrophs in the mycorhizosphere are discussed.

Symbiotic efficiency of autochthonous arbuscular mycorrhizal fungus (G. mosseae) and Brevibacillus sp. isolated from cadmium polluted soil under increasing cadmium levels

The effect of inoculation with indigenous naturally occurring microorganisms (an arbuscular mycorrhizal (AM) fungus and rhizosphere bacteria) isolated from a Cd polluted soil was assayed on Trifolium repens growing in soil contaminated with a range of Cd. One of the bacterial isolate showed a marked PGPR effect and was identified as a Brevibacillus sp. Mycorrhizal colonization also enhanced Trifolium growth and N, P, Zn and Ni content and the dually inoculated (AM fungus plus Brevibacillus sp.) plants achieved further growth and nutrition and less Cd concentration, particularly at the highest Cd level. Increasing Cd level in the soil decreased Zn and Pb shoot accumulation. Coinoculation of Brevibacillus sp. and AM fungus increased shoot biomass over single mycorrhizal plants by 18% (at 13.6 mg Cd kg(-1)), 26% (at 33.0 mg Cd kg(-1)) and 35% (at 85.1 mg Cd (kg(1)). In contrast, Cd transfer from soil to plants was substantially reduced and at the highest Cd level Brevibacillus sp. lowered this value by 37.5% in AM plants. Increasing Cd level highly reduced plant mycorrhization and nodulation. Strong positive effect of the bacterium on inocula, are important in plant Cd tolerance and development in Cd polluted soils.

Significance of treated agrowaste residue and autochthonous inoculates (Arbuscular mycorrhizal fungi and Bacillus cereus) on bacterial community structure and phytoextraction to remediate soils contaminated with heavy metals

In this study, we analyzed the impact of treatments such as Aspergillus niger-treated sugar beet waste (SB), PO4(3-) fertilization and autochthonous inoculants [arbuscular mycorrhizal (AM) fungi and Bacillus cereus], on the bacterial community structure in a soils contaminated with heavy metals as well as, the effectiveness on plant growth (Trifolium repens). The inoculation with AM fungi in SB amended soil, increased plant growth similarly to PO4(3-) addition, and both treatments matched in P acquisition but bacterial biodiversity estimated by denaturing gradient gel electrophoresis of amplified 16S rDNA sequences, was more stimulated by the presence of the AM fungus than by PO4(3-) fertilization. The SB amendment plus AM inoculation increased the microbial diversity by 233% and also changed (by 215%) the structure of the bacterial community. The microbial inoculants and amendment used favoured plant growth and the phytoextraction process and concomitantly modified bacterial community in the rhizosphere; thus they can be used for remediation. Therefore, the understanding of such microbial ecological aspects is important for phytoremediation and the recovery of contaminated soils.

Endophytic Burkholderia fungorum DBT1 can improve phytoremediation efficiency of polycyclic aromatic hydrocarbons

Burkholderia fungorum DBT1 is a bacterial strain isolated from an oil refinery discharge and capable of transforming dibenzothiophene, phenanthrene, naphthalene, and fluorene. In order to evaluate the influence of a policyclic aromatic hydrocarbon (PAH)-transforming bacterial strain on the phytoremediation of organic contaminants, B. fungorum DBT1 was inoculated into hybrid poplar (Populus deltoides×Populus nigra). The poplar plants were grown for 18-wk with or without naphthalene, phenanthrene, fluorene and dibenzothiophene (488mgkg(-1) soil each) in non-sterile sand-peat substrate. Evidences were gained that B. fungorum DBT1 was present in high concentration in poplar root tissues (2.9-9.5×10(3)CFUg(-1)), while the strain was not detected in stem, leaves and rhizosphere. When poplar was planted in uncontaminated substrate, the infection caused negative effects on biomass index, leaves and stem dry weight, without showing however any disease symptoms. On the other hand, plants inoculated with the strain DBT1 resulted in better tolerance against the toxic effects of PAHs, in terms of root dry weight. Although the presence of plants acted as the main effective treatment for PAH dissipation (82-87%), the inoculum with DBT1 strain lead to the highest PAH abatement (up to 99%). In the present study, an environmental isolate with proper metabolic features was demonstrated to be possibly suitable as a poplar endophyte for improving microbe-assisted phytoremediation in PAH contaminated matrices.

Effectiveness of autochthonous bacterium and mycorrhizal fungus on Trifolium growth, symbiotic development and soil enzymatic activities in Zn contaminated soil

Aims:  This study investigates how autochthonous micro‐organisms [bacterium and/or arbuscular mycorrhizal (AM) fungi] affected plant tolerance to Zn contamination.

Arbuscular mycorrhizal effect on heavy metal uptake of ryegrass (Lolium p erenne L.) in pot culture with polluted soils

The aim of the present study was to study the effect of metal-adapted and non-adapted arbuscular mycorrhizal fungi (AMF) on metal uptake by the host plant in two pot experiments. The soil samples originated from a Cd, Ni and Zn-polluted calcareous chernozem. Ryegrass (Lolium perenne L.) was used as a test plant. Changes in the parameters of mycorrhizal root colonization and the metal uptake of the host as affected by metal type, metal rate, and mycorrhizal treatments were investigated. A more efficient mycorrhizal symbiosis can develop, if heavy metal-tolerant AM fungi are present in the metal-polluted soil. Cadmium, Ni-, and Zn-transfer from soil to plant was lower in plants with mycorrhizal symbiosis. Cadmium, Ni- and Zn-tolerance of AMF can be different, depending whether the AMF originated from metal-polluted or not-polluted soils.

Symbiont effect of rhizobium bacteria and vesicular arbuscular mycorrhizal fungi on Pisum sativum in recultivated mine spoils

The frequency (F%) of spontaneous endomycorrhizal fungal infection (AMF) and the root nodulation of Pisum sativum L. was studied after 8 and 15 years of recultivation in 4 soils (andesitic tuff, yellow sand, yellow clay, and grey clay) disturbed by mining activities. The effects of Rhizobium inoculation and the interaction of both microsymbionts with plant production were also examined, along with humus content and the humus stability coefficient, in the following variations: control, NPK fertilizer, NPK + lignite, NPK + straw, and sewage sludge. Dump spoils originating from deep geological layers were poor in organic materials. After 12 years of recultivation, the humus content increased significantly. No such increase was noted in grey clay and the natural, brown forest soil used as an undisturbed (control) sample. The degradation of soils by mining brings about a decrease in the rhizobial and mycorrhizal population, so the number of spontaneous Rhizobium nodules is relatively low and does not influence...

Vertical and horizontal distributions of microbial abundances and enzymatic activities in propylene-glycol-affected soils

The natural microbial activity in the unsaturated soil is vital for protecting groundwater in areas where high loads of biodegradable contaminants are supplied to the surface, which usually is the case for airports using aircraft de-icing fluids (ADF) in the cold season. Horizontal and vertical distributions of microbial abundance were assessed along the western runway of Oslo Airport (Gardermoen, Norway) to monitor the effect of ADF dispersion with special reference to the component with the highest chemical oxygen demand (COD), propylene glycol (PG). Microbial abundance was evaluated by several biondicators: colony-forming units (CFU) of some physiological groups (aerobic and anaerobic heterotrophs and microscopic fungi), most probable numbers (MPN) of PG degraders, selected catabolic enzymatic activities (fluorescein diacetate (FDA) hydrolase, dehydrogenase, and β-glucosidase). High correlations were found between the enzymatic activities and microbial counts in vertical soil profiles. All microbial abundance indicators showed a steep drop in the first meter of soil depth. The vertical distribution of microbial abundance can be correlated by a decreasing exponential function of depth. The horizontal trend of microbial abundance (evaluated as total aerobic CFU, MPN of PG-degraders, and FDA hydrolase activity) assessed in the surface soil at an increasing distance from the runway is correlated negatively with the PG and COD loads, suggesting the relevance of other chemicals in the modulation of microbial growth. The possible role of potassium formate, component of runway de-icers, has been tested in the laboratory by using mixed cultures of Pseudomonas spp., obtained by enrichment with a selective PG medium from soil samples taken at the most contaminated area near the runway. The inhibitory effect of formate on the growth of PG degraders is proven by the reduction of biomass yield on PG in the presence of formate.

Laboratory-scale evaluation of a combined soil amendment for the enhanced biodegradation of propylene glycol-based aircraft de-icing fluids.

A combined soil amendment was tested in microcosm experiments with an aim to enhance the aerobic biodegradation of propylene glycol (PG)-based aircraft de-icing fluids during and following the infiltration of contaminated snowmelt. A key objective under field conditions is to increase degradation of organic pollutants in the surface soil where higher microbial activity and plant rhizosphere effects may contribute to a more efficient biodegradation of PG, compared to subsoil ground layers, where electron acceptors and nutrients are often depleted. Microcosm experiments were set up in Petri dishes using 50 g of soil mixed with appropriate additives. The samples contained an initial de-icing fluid concentration of 10,000 mg/kg soil. A combined amendment using calcium peroxide, activated carbon and 1×Hoagland solution resulted in significantly higher degradation rates for PG both at 4 and 22°C. Most probable numbers of bacteria capable of utilizing 10,000 mg/kg de-icing fluid as a sole carbon source were about two orders of magnitude higher in the amended soil samples compared to unamended controls at both temperatures. The elevated numbers of such bacteria in surface soil may be a source of cells transported to the subsoil by snowmelt infiltration. The near-surface application of amendments tested here may enhance the growth of plants and plant roots in the contaminated area, as well as microbes to be found at greater depth, and hence increase the degradation of a contaminant plume present in the ground.