Edmundo Rosique-Gil

Microfungal oasis in an oligotrophic desert: diversity patterns and community structure in three freshwater systems of Cuatro Ciénegas, Mexico

The Cuatro Ciénegas Basin (CCB) comprises several oligotrophic aquatic ecosystems limited by phosphorus. These aquatic systems are dominated by a high prokaryotic diversity, shaped by the stress of low nutrient supplies and interspecific competition. Although fungi constitute a diverse and important component of microbial diversity, the microfungal diversity in the CCB remains to be unveiled. With the aim to explore microfungal diversity and ecological patterns in this area, we present the first investigation analyzing cultivable taxa from sediment and water, as well as lignocellulolytic taxa obtained from incubated submerged plant debris, and wood panels in three contrasting freshwater systems in the CCB: Churince, Becerra and Pozas Rojas. We chose a culture-based approach to analyze sediment and water samples in order to obtain fungal cultures, providing opportunities for a posteriori studies, and the possibility of ex situ preservation of the diversity. We evaluated sequence data from the nuclear ribosomal internal transcribed spacer including the 5.8 rDNA region for 126 isolates, revealing 37 OTUs. These OTUs were phylogenetically affiliated to several genera in the fungal phyla: Zygomycota, Basidiomycota, and Ascomycota. We recorded two OTUs with saline affinity, agreeing with previous findings on the prokaryotic communities with ancestral marine resemblances. All the studied systems showed moderate diversity levels, however discrepancies among the diversity indexes were observed, due to the occurrence of abundant taxa in the samples. Our results indicated that lignocellulolytic microfungal communities are dominated by transient fungal taxa, as resident species were not recorded perhaps as a result of the long-term strong competition with the highly adapted prokaryotic community. Moreover, the obtained microfungal taxa occurred mostly on the resident plant debris, rather than submerged wood panels, perhaps as a result of the high adaptation to specific environmental conditions. In conclusion, the CCB possess a moderate taxonomical diversity compared to other arid environments, probably as a result of high selective pressures. Nonetheless, due to high spatial and temporal heterogeneity, the functional fungal diversity was considerable as predicted by the intermediate disturbance hypothesis. Decisively, the assessment of microfungal diversity freshwater systems is relevant, since this ecological group of microorganisms represents an important indicator of trophic complexity and biotic interactions among microbial communities, having important implications for understanding eukaryotic survival at the oligotrophic limit for life.

Diversity of marine ascomycetes from the disturbed sandy beaches of Tabasco, Mexico

The coastline of Tabasco State in the Gulf of Mexico represents a highly deteriorated ecosystem, where densely populated human settlements and large offshore petroleum developments are negatively affecting the marine biodiversity. Previous work on marine ascomycetes reported that in the Gulf of Mexico the diversity of these fungi might be threatened by anthropogenic activities. Therefore we evaluated the diversity of marine ascomycetes in this area, and registered 19 taxa. Ceriosporopsis capillacea was recorded for the first time for Mexico. The highest diversity was obtained in the beach of Sanchez Magallanes, which receives a great quantity and diversity of organic remains originating from El Carmen/Machona mangrove forests via the Santa Ana mouth, benefiting the proliferation of marine fungi. The lowest diversity was documented in the beach of Paraiso, which is close to the delta of one of the most polluted rivers in Mexico and to off-shore oil extraction platforms. We found a significant correlation between the community composition and abundance, implying that the overall abundance is defined by the community structure, perhaps as a result of competition. Additionally, our results indicated that there is no relationship between the grain size and the biodiversity observed.

Analysis of the Sporulating Microfungal Community in Decomposing Fallen Leaves of Rinorea guatemalensis (Wats.) Bartlett (Malphigiales, Violaceae) in a Mexican Rainforest

Abstract In Mexico, the study of the composition and changes of the sporulating microfungi on decaying fallen leaves in rainforest ecosystems has not been elucidated. In this study, we evaluated the species richness, diversity, abundance and similarity of the sporulating microfungi inhabiting the leaf litter of Rinorea guatemalensis, a dominant evergreen tree in family Violaceae (Malphigiales) from the rainforest of the “Agua Bianca” park in the state of Tabasco. The study was done over a period of 210 days. In parallel we analyzed the loss of leaf biomass. The litter bag method was used. Fungal fruiting structures were detected and quantified using moist chambers. A total of 38 taxa were detected. Two main phases were detected in the biomass loss and in the changes in the microfungi community; the primary phase was characterized by the highest biomass loss and corresponded with the highest diversity, specific richness, as well the highest values of frequency of occurrence for the sporulating microfungi. In the secondary phase the biomass loss and diversity remain with little apparent changes and with a tendency of decrease gradually with increasing foliar decomposition. In the later stages of decomposition, the similarity in the microfungal community increased. The frequency and periodicity of occurrence values indicated that the sporulating microfungi community was structured mainly by rare and sporadic species. Cylindrocladium scoparium, Microthyrium sp., Volutella ciliata and Volutella minima were considered as residents throughout the study. fungal diversity / leaf litter / leaf decomposition / Mexico / tropical microfungi