Enriqueta Amora-Lazcano

Effect of the inoculation of Axonopus affinis plantlets with immobilized rhizobacteria exposed to cadmium

The interactions between plants with rhizosphere and root associated microorganisms have been considered because they are potentially useful in phytoremediation and are used as microbial inoculates (biofertilizers) that give bioprotection to plants against biotic and abiotic stresses. One of the methods safe and effective for introducing bioinoculants is the encapsulation of cells in biodegradable gel matrices like alginate. The aim of this study is to evaluate the effect of three rhizobacteria (

Comparison of plant growth-promoting rhizobacteria in a pine forest soil and an agricultural soil

The load and diversity of plant growth-promoting rhizobacteria (PGPR) are used as biomarkers to evaluate the health and quality of the soil. In the present study, the diversity of PGPRs and the physicochemical properties of the soil were used as comparative biomarkers in two adjacent soils (a pine forest soil and an agricultural soil) of the same region in Mexico City in order to investigate the effects of land use change. Bacterial diversity and physicochemical properties differed between the two soils. In the pine forest soil, PGPR were distributed at similar proportions in the Proteobacteria (29.41%), Actinobacteria (29.41%) and Firmicutes (35.29%) phyla, whereas the remaining PGPR were in Bacteroidetes (5.88%). In the agricultural soil, most PGPR belonged to the Phylum Firmicutes (50%), with the remaining belonging to Proteobacteria (22.73%), Actinobacteria (18.18%) and Bacteroidetes (9.09%). Percentages of bacteria producing indole acetic acid (90.91%) and siderophores (40.91%) were higher in agricultural soil. A canonical correspondence analysis (CCA) was used to correlate PGPR with the physicochemical characteristics of the soils. The CCA revealed that differences between both soils and the physicochemical properties of the soils affected isolated bacterial species and their distribution. These results demonstrate that the PGPR are correlated with the physicochemical properties of the soil, exhibiting differences between an agricultural soil and a pine forest soil.

Analysis of the Ectomycorrhizal Enzymatic Functional Diversity of Fagus mexicana

In forest ecosystems, ectomycorrhizal symbiosis is able to produce a large range of extracellular and cell wall-bound enzymes which hydrolyze compounds contained in soil organic matter. Enzymatic activity profiles of individual ectomycorrhiza have value of functional traits to characterize the diversity of ectomycorrhizal (ECM) communities. Fagus mexicana is an endemic and only species that has restricted distribution to cloud forest of Sierra Madre Oriental in México and there are few works focused to the relationship between this forest species and ectomycorrhizal, which enhance its growth and development. This work analyzes the enzyme functional diversity of ectomycorrhizal fungi associated to F. mexicana trees of different ages. In this study, the ECM species: Cantharellus cibarius Fr., Laccaria amethystina Cook, Lactarius subdulcis (Pers.) gray and Xathoconium separans (Peck) Halling & Both, were founded near these trees and the influence of the niche on the mean catabolic activity of ectomycorrhizal community, varied according to the dominant substrate; where L. amethystina and X. separans presented the highest β-glucosidase and acid phosphatase activities in F. mexicana tips. The enzymatic profiles demonstrated a functional plasticity of the ectomycorrhizal species associated to the age of trees tested and also could be a trait of their capability of adaptation to the cloud forest ecosystem.

Photosynthetic sulfur bacteria from Zimapan Reservoir (Mexico): Seasonal variations and toxic effects of zinc in a microcosm system

Photosynthetic sulfur bacteria oxidize the sulfide produced by dissimilatory sulfate-reducing bacteria, thus preventing the occurrence of pollution by these compounds in the oxygenic zone of aquatic systems. Zinc is one of the most abundant heavy metals. Its toxic effects have been documented in various organisms that can photosynthesize, but a lack of information prevails in this respect, about photosynthetic sulfur bacteria. The aim of the present study was to evaluate the toxic effects of zinc on green sulfur bacteria (Chlorobiaceae) and purple sulfur bacteria (Chromatiaceae) in a microcosm as well to explore the possible relationships between the bacterial population growths with the physicochemical properties of the metalimnion of Zimapan Reservoir (Mexico) during a 1-year period. Hydrosoluble organic carbon (HOC) and light availability in the metalimnion were the limiting factors for growth in these bacteria. Higher HOC levels occurred in Spring, at the end of the wet season and in Winter. Current zinc levels in the reservoir seem to elicit toxic effects. At lethal zinc concentrations, the best concentration-response relationship was shown. The biomarker for purple sulfur bacteria was the bacteriochlorophyll content, while total reducing sugar was the best biomarker for green sulfur bacteria. At sublethal concentrations, zinc alters adenosine triphosphate levels, total reducing sugar, total protein content, and bacteriochlorophyll content. The observed responses indicate that green sulfur bacteria are more sensitive than purple sulfur bacteria and are suitable target organisms for use in establishing the accepted threshold concentration of zinc (NOEC 0.056–0.097 mg L−1 of Zn) in anoxic deep water.