NaCl Modifies Biochemical Traits in Bacterial Endophytes Isolated from Halophytes: Towards Salinity Stress Mitigation Using Consortia.

Bacterial endophytes (120) were isolated from six halophytes (Distichlis spicata, Cynodon dactylon, Eragrostis obtusiflora, Suaeda torreyana, Kochia scoparia, and Baccharis salicifolia). These halophiles were molecularly identified and characterized with or without NaCl conditions. Characterization was based on tests such as indole acetic acid (IAA), exopolysaccharides (EPS), and siderophores (SID) production; solubilization of phosphate (P), potassium (K), zinc (Zn), and manganese (Mn); mineralization of phytate; enzymatic activity (acid and alkaline phosphatase, phytases, xylanases, and chitinases) and the mineralization/solubilization mechanisms involved (organic acids and sugars). Moreover, compatibility among bacteria was assessed. Eleven halophiles were characterized as highly tolerant to NaCl (2.5 M). The bacteria isolated were all different from each other. Two belonged to Bacillus velezensis and one to B. pumilus while the rest of bacteria were identified up to the genus level as belonging to Bacillus, Halobacillus, Halomonas, Pseudomonas, Nesterenkonia, and three strains of Oceanobacillus. The biochemical responses of nutrient solubilization and enzymatic activity were different between bacteria and were influenced by the presence of NaCl. Organic acids were involved in P mineralization and nutrient solubilization. Tartaric acid was common in the solubilization of P, Zn, and K. Maleic and vanillic acid were only detected in Zn and K solubilization, respectively. Furthermore, sugars appeared to be involved in the solubilization of nutrients; fructose was detected in the solubilization tests. Therefore, these biochemical bacterial characteristics should be corroborated in vivo and tested as a consortium to mitigate saline stress in glycophytes under a global climate change scheme that threatens to exacerbate soil salinity.

Biochemical Response of the Endogeic Earthworm (Balanteodrilus extremus) Exposed to Tropical Soils.

This work evaluated the biochemical responses of the endogeic earthworm Balanteodrilus extremus exposed for 14 and 48 days (d) to soils collected from two tropical agricultural systems: maize-sorghum (MS) and soybean-sorghum (SS). A soil without agricultural management (WAM) and the use of pesticides was selected as a reference. The presence of organochlorine (OC) and organophosphate (OP) pesticide residues was quantified in MS and SS soils. Biomarkers of detoxification [glutathione S transferase (GST)], neurotoxicity [acetylcholinesterase (AChE)] and oxidative stress [superoxide dismutase (SOD), catalase (CAT) and lipoperoxidation (LPO)] were evaluated in B. extremus. The concentration of OP pesticide residues was higher in SS than in MS. Activity of AChE in B. extremus exposed to SS soil for 14 d was significantly more inhibited (78%) than in MS soil (68%). B. extremus has been shown to be a good bioindicator of contaminated soils in tropical regions.

Selection of Salinity-Adapted Endorhizal Fungal Consortia from Two Inoculum Sources and Six Halophyte Plants.

Soil salinity is a limiting factor in crop productivity. Inoculating crops with microorganisms adapted to salt stress is an alternative to increasing plant salinity tolerance. Few studies have simultaneously propagated arbuscular mycorrhizal fungi (AMF) and dark septate fungi (DSF) using different sources of native inoculum from halophyte plants and evaluated their effectiveness. In alfalfa plants as trap culture, this study assessed the infectivity of 38 microbial consortia native from rhizosphere soil (19) or roots (19) from six halophyte plants, as well as their effectiveness in mitigating salinity stress. Inoculation with soil resulted in 26-56% colonization by AMF and 12-32% by DSF. Root inoculation produced 10-56% and 8-24% colonization by AMF and DSF, respectively. There was no difference in the number of spores of AMF produced with both inoculum types. The effective consortia were selected based on low Na but high P and K shoot concentrations that are variable and are relevant for plant nutrition and salt stress mitigation. This microbial consortia selection may be a novel and applicable model, which would allow the production of native microbial inoculants adapted to salinity to diminish the harmful effects of salinity stress in glycophyte plants in the context of sustainable agriculture.

Metal(loid) bioaccessibility of atmospheric particulate matter from mine tailings at Zimapan, Mexico.

Metal(loid)s are contaminants of concern emitted as particulate matter (PM) from several pollution sources. The objective was to characterize potential exposure from local airborne metal(loid)s in a community in proximity to mine tailings. Air samples were collected weekly at five sites around the municipal mine tailings using two Hi-volume samplers for simultaneously collecting PM10 and PM2.5. Total suspended particulates (TSP), concentrations, speciation, and bioaccessibility of metal(loid)s were quantified. The size and form of particles were determined by scanning electron microscopy. The concentration of TSP (µg m-3) in the airborne samples ranged from 21.2 to 64.6 for PM2.5 and 23.6 to 80.1 for PM10. The profiles of analyzed quasi-total metal(loid) concentration from all sampling sites were similar between these aerosols PM sizes except at site 2 for Cd, at site 3 for Cu, and site 4 for Zn. The order of quasi-total metal(loid) concentration, in the airborne samples for both PM sizes, was As > Zn > Fe > Pb > Cu > Mn > Cd. As speciation included As-sulfite, As(III)-O, and As(V)-O with less concentration of As(III)-O in both PM sizes. Bioaccessible metal(loid) concentrations were very high and represented a great percentage from the quasi-total airborne concentrations, for instance, 10% and 37% for Pb and 8% and 6% for As in pulmonary and gastric bioaccessible concentrations, respectively. Knowing the toxic effects of these pollutants, there is an urgent need to establish environmental regulation of bioaccessible pollutant concentrations from PM dislodged from uncovered metal(loid) mine tailings affecting not only nearby human populations but also possible long-distance ecosystem transport.

Screening bacterial phosphate solubilization with bulk-tricalcium phosphate and hydroxyapatite nanoparticles.

Phosphate-solubilizing bacteria can release phosphorus (P) from insoluble minerals and benefit either soil fitness or plant growth. Bulk sized P compounds have been suggested but little is known about solubilization of nanosized materials such as hydroxyapatite nanoparticles (HANP). A screening of the initial 43 strains from vanilla rhizospheres for phosphate solubilization with bulk Ca3(PO4)2 was carried out. Subsequently, 6 strains were selected on bulk rock phosphate (RP) and HANP. Two kinetics experiments were run out regarding evaluation at 5, 10 and 20 days after inoculation (dai). Bacterial biomass production was similar in both experiments; the lowest biomass was found at 20 dai. In all cases, bacteria reduced the original culture medium pH; which was related with phosphate solubilization from the production of organic acids. Citric acid was produced by all strains. Enterobacter cloacae CP 31 was the most interesting bacterium: produced the lowest culture pH at 20 dai (4) with both Ca3(PO4)2 and RP, and 3.7 at 10 dai with HANP correlating with high soluble P concentration (536, 64 and 13 mg L-1 with these P sources, respectively). This bacterium should be tested as an inoculant in plants to reveal its potential as plant promoter growth and HANP to suggest its role in the potential use of nano-P fertilizers.

Phytobarriers: Plants capture particles containing potentially toxic elements originating from mine tailings in semiarid regions.

Retention of particles containing potentially toxic elements (PTEs) on plants that spontaneously colonize mine tailings was studied through comparison of washed and unwashed shoot samples. Zn, Pb, Cd, Cu, Ni, Co and Mn concentrations were determined in plant samples. Particles retained on leaves were examined by Scanning Electronic Microscopy and energy dispersive X-Ray analysis. Particles containing PTEs were detected on both washed and unwashed leaves. This indicates that the thorough washing procedure did not remove all the particles containing PTEs from the leaf surface, leading to an overestimation of the concentrations of PTEs in plant tissues. Particularly trichomes and fungal mycelium were retaining particles. The quantity and composition of particles varied among plant species and place of collection. It is obvious that plants growing on toxic mine tailings form a physical barrier against particle dispersion and hence limit the spread of PTEs by wind.