Phosphonate consumers potentially contributing to methane production in Brazilian soda lakes

Oxic methane production (OMP) has been reported to significantly contribute to methane emissions from oxic surface waters. Demethylation of organic compounds, photosynthesis-associated methane production, and (bacterio)chlorophyll reduction activity are some of the investigated mechanisms as potential OMP sources related to photosynthetic organisms. Recently, cyanobacteria have often been correlated with methane accumulation and emission in freshwater, marine, and saline systems. The Brazilian Pantanal is the world's largest wetland system, with approximately 10,000 shallow lakes, most of which are highly alkaline and saline extreme environments. We initiated this study with an overall investigation using genetic markers, from which we explored metagenomic and limnological data from the Pantanal soda for five potential OMP pathways. Our results showed a strong positive correlation between dissolved methane concentrations and bloom events. Metagenomic data and nutrients, mainly orthophosphate, nitrogen, iron, and methane concentrations, suggest that the organic phosphorous demethylation pathway has the most potential to drive OMP in lakes with blooms. A specialized bacterial community was identified, including the Cyanobacteria Raphidiopsis, although the bloom does not contain the genes to carry out this process. These data showed enough evidence to infer the occurrence of an OMP pathway at Pantanal soda lakes, including the microbial sources and their relation to the cyanobacterial blooms.

Coffea arabica seedlings genotypes are tolerant to high induced selenium stress: Evidence from physiological plant responses and antioxidative performance

Selenium (Se) is considered a beneficial element to higher plants based on its regulation of antioxidative system under abiotic or biotic stresses. However, the limit of beneficial and toxic physiological effects of Se is very narrow. In the present study, the antioxidant performance, nutritional composition, long-distance transport of Se, photosynthetic pigments, and growth of Coffea arabica genotypes in response to Se concentration in solution were evaluated. Five Coffea arabica genotypes (Obatã, IPR99, IAC125, IPR100 and Catucaí) were used, which were grown in the absence and presence of Se (0 and 1.0 mmol L^-1) in nutrient solution. The application of 1 mmol L^-1 Se promoted root browning in all genotypes. There were no visual symptoms of leaf toxicity, but there was a reduction in the concentration of phosphorus and sulfur in the shoots of plants exposed to high Se concentration. Except for genotype Obatã, the coffee seedlings presented strategies for regulating Se uptake by reducing long-distance transport of Se from roots to shoots. The concentrations of total chlorophyll, total pheophytin, and carotenoids were negatively affected in genotypes Obatã, IPR99, and IAC125 upon exposure to Se at 1 mmol L^-1. H₂O₂ production was reduced in genotypes IPR99, IPR100, and IAC125 upon exposure to Se, resulting in lower activity of superoxide dismutase (SOD), and catalase (CAT). These results suggest that antioxidant metabolism was effective in regulating oxidative stress in plants treated with Se. The increase in sucrose, and decrease in SOD, CAT and ascorbate peroxidase (APX) activities, as well as Se compartmentalization in the roots, were the main biochemical and physiological modulatory effects of coffee seedlings under stress conditions due to excess of Se.

Characterization of genetic diversity on tropical Trichoderma germplasm by sequencing of rRNA internal transcribed spacers

Objective

Trichoderma species are found in soil and in association with plants. They can act directly or indirectly in the biological control of plant diseases and in the promotion of plant growth, being among the most used fungi in the formulation of bioproducts applied to agricultural systems. The main objective of this study was to characterize at a first-tier level a collection of 67 Trichoderma isolates from various tropical sources, based solely on sequencing of the internal transcribed spacer (ITS) region of the rRNA genes. Our goal was to provide a preliminary idea of the baseline diversity in this collection, to combine this information later with an array of other isolate-specific physiological data. This study provides a required knowledge at molecular level for assessment of this germplasm potential as a source of biotechnological products for beneficial effects in plants.

Results

Sequencing of the ITS region showed that the 67 Trichoderma isolates belonged in 11 species: T. asperellum, T. atroviride, T. brevicompactum, T. harzianum, T. koningiopsis, T. longibrachiatum, T. pleuroticola, T. reesei, T. spirale, T. stromaticum and T. virens. A total of 40.3% of the isolates were very closely related to each other and similar to T. harzianum. The baseline genetic diversity found indicates that the collection has different genotypes, which can be exploited further as a source of bioproducts, aiming at providing beneficial effects to plants of interest to cope with biotic and abiotic stresses.