Aquatic Hyphomycete Taxonomic Relatedness Translates into Lower Genetic Divergence of the Nitrate Reductase Gene

Aquatic hyphomycetes are key microbial decomposers in freshwater that are capable of producing extracellular enzymes targeting complex molecules of leaf litter, thus, being crucial to nutrient cycling in these ecosystems. These fungi are also able to assimilate nutrients (e.g., nitrogen) from stream water, immobilizing these nutrients in the decomposing leaf litter and increasing its nutritional value for higher trophic levels. Evaluating the aquatic hyphomycete functional genetic diversity is, thus, pivotal to understanding the potential impacts of biodiversity loss on nutrient cycling in freshwater. In this work, the inter- and intraspecific taxonomic (ITS1-5.8S-ITS2 region) and functional (nitrate reductase gene) diversity of 40 aquatic hyphomycete strains, belonging to 23 species, was evaluated. A positive correlation was found between the taxonomic and nitrate reductase gene divergences. Interestingly, some cases challenged this trend: Dactylella cylindrospora (Orbiliomycetes) and Thelonectria rubi (Sordariomycetes), which were phylogenetically identical but highly divergent regarding the nitrate reductase gene; and Collembolispora barbata (incertae sedis) and Tetracladium apiense (Leotiomycetes), which exhibited moderate taxonomic divergence but no divergence in the nitrate reductase gene. Additionally, Tricladium chaetocladium (Leotiomycetes) strains were phylogenetically identical but displayed a degree of nitrate reductase gene divergence above the average for the interspecific level. Overall, both inter- and intraspecific functional diversity were observed among aquatic hyphomycetes.

Two new asexual genera and six new asexual species in the family Microthyriaceae (Dothideomycetes, Ascomycota) from China

The family Microthyriaceae is represented by relatively few mycelial cultures and DNA sequences; as a result, the taxonomy and classification of this group of organisms remain poorly understood. During the investigation of the diversity of aquatic hyphomycetes from southern China, several isolates were collected. These isolates were cultured and sequenced and a BLAST search of its LSU sequences against data in GenBank revealed that the closest related taxa are in the genus Microthyrium. Phylogenetic analyses, based on the combined sequence data from the internal transcribed spacers (ITS) and the large subunit (LSU), revealed that these isolates represent eight new taxa in Microthyriaceae, including two new genera, Antidactylariagen. nov. and Isthmomycesgen. nov. and six new species, Antidactylaria minifimbriatasp. nov., Isthmomyces oxysporussp. nov., I. dissimilissp. nov., I. macrosporussp. nov., Triscelophorus anisopterioideussp. nov. and T. sinensissp. nov. These new taxa are described, illustrated for their morphologies and compared with similar taxa. In addition, two new combinations are proposed in this family.

Aquapteridospora Jiangxiensis sp. Nov., A New Aquatic Hyphomycetes From Freshwater Habitats in China and A. Bambusinum Comb. Nov.

During an investigation of freshwater fungi in Jiangxi province, China, a new hyphomycetous species, Aquapteridospora jiangxiensis, was collected and isolated. A. jiangxiensis is characterized by its unbranched and guttulate conidiophores with multi-septa and swollen at the base, polyblastic conidiogenous cells with sympodial proliferations and denticles, guttulate conidia with a sheath. The new species was illustrated and a muti-loci (ITS, LSU, SSU, TEF1 and RPB2) phylogenetic tree was constructed. Pleurophragmium bambusinum was is transferred to Aquapteridospora based on molecular and morphological data. A key to the species of Aquapteridospora is presented in this paper.

Litter Quality Is a Stronger Driver than Temperature of Early Microbial Decomposition in Oligotrophic Streams: a Microcosm Study

Litter decomposition is an ecological process of key importance for forest headwater stream functioning, with repercussions for the global carbon cycle. The process is directly and indirectly mediated by microbial decomposers, mostly aquatic hyphomycetes, and influenced by environmental and biological factors such as water temperature and litter quality. These two factors are forecasted to change globally within the next few decades, in ways that may have contrasting effects on microbial-induced litter decomposition: while warming is expected to enhance microbial performance, the reduction in litter quality due to increased atmospheric carbon dioxide and community composition alteration may have the opposite outcome. We explored this issue through a microcosm experiment focused on early microbial-mediated litter decomposition under stream oligotrophic conditions, by simultaneously manipulating water temperature (10 °C and 15 °C) and litter quality (12 broadleaf plant species classified into 4 categories based on initial concentrations of nitrogen and tannins). We assessed potential changes in microbial-mediated litter decomposition and the performance of fungal decomposers (i.e., microbial respiration, biomass accrual, and sporulation rate) and species richness. We found stronger effects of litter quality, which enhanced the performance of microbial decomposers and decomposition rates, than temperature, which barely influenced any of the studied variables. Our results suggest that poorer litter quality associated with global change will have a major repercussion on stream ecosystem functioning.

Keqinzhangia Aquatica Gen. et sp. nov. And Pseudocoronospora Hainanense gen. et sp. nov., Isolated From Freshwater In Southern China

During the investigation of the diversity of aquatic hyphomycetes from southern China, two interesting isolates were collected. Then, the two isolates were cultured and sequenced, and a BLAST search of its LSU sequences against data in GenBank revealed that the closest related taxa in the genus Microthyrium. Phylogenetic analyses, based on the combined sequence data from the small and large nuclear subunit ribosomal DNA (SSU and LSU), revealed that our isolates belong to the Microthyriaceae. Combined morphological characters, we finally described our isolates as two new genera and species in Microthyriaceae, named as: Keqinzhangia aquatica and Pseudocoronospora hainanense. The full descriptions, illustrations and a phylogenetic tree showing the position of the two new genera were provided in this paper.

Phylogenetic Analyses of New Aquatic Hyphomycetes Provide Molecular Evidence for Microthyriaceae (Dothideomycetes, Ascomycota) Anamorph

The fungal family Microthyriaceae is represented by relatively few mycelial cultures and DNA sequences. As a result, the taxonomy and classification of this group of organisms remain poorly understood. Here, based on DNA sequences at four gene fragments (nuLSU rDNA, nuSSU rDNA, TEF1 and RPB2) in our analyses of aquatic hyphomycetes from southern China, we identify and report four new genera (Antidactylaria, Isthmomyces, Keqinzhangia, Pseudocoronospora) and thirteen new species (Antidactylaria minifimbriata, Pseudocoronospora hainanensis, Isthmomyces oxysporus, I. dissimilis, I. macrosporus, I. relanceatus, Keqinzhangia aquatica, Triscelophorus anakonajensis, T. anisopterioides, T. guizhouensis, T. mugecuoensis, T. multibrachiatus, T. neoseptatus; new combinations Isthmomyces asymmetrica, I. basitruncata, I. geniculata, I. lanceata, I. minima, I. rotundata) belonging to Microthyriaceae. Our results provided the first molecular evidence of asexual morph of this family and strengthened the phylogenetic placement of the family in class Dothideomycetes. The addition of these new taxa made Microthyriaceae the largest family comprising freshwater asexual genera in Pleosporomycetidae. In addition, we confirmed the monophyly of the genus Triscelophorus, the paraphyly of the genus Isthmolongispora, and revised 6 new combinations in Isthmolongispora. ITS barcoding of 13 species were also provided to help identify aquatic hyphomycetes in the future. Our results suggest that the asexual genera and sexual genera identified so far within this family have completely different ecological niches.

Fungal richness does not buffer the effects of streams salinization on litter decomposition

Freshwater salinization is a world-wide phenomenon threatening stream communities and ecosystem functioning. In these systems, litter decomposition is a main ecosystem-level process where fungi (aquatic hyphomycetes) play a central role linking basal resource and higher levels of food-web. The current study evaluated the impact of aquatic hyphomycete richness on leaf litter decomposition when subjected to salinization. In a microcosm study, we analysed leaf mass loss, fungal biomass, respiration and sporulation rate by fungal assemblages at three levels of species richness (1, 4, 8 species) and three levels of salinity (0, 8, 16 g NaCl L‑1). Mass loss and sporulation rate were depressed at 8 and 16 g NaCl L‑1, while fungal biomass and respiration were only negatively affected at 16 g L‑1. A richness effect was only observed on sporulation rates, with the maximum values found in assemblages of 4 species. In all cases, the negative effects of high levels of salinization on the four tested variables superimposed the potential buffer capacity of fungal richness. The study suggests functional redundancy among the fungal species even at elevated salt stress conditions which may guarantee stream functioning at extreme levels of salinity. Nonetheless, it also points to the possible importance of salt induced changes on fungal diversity and identity in salinized streams able to induce bottom-up effects in the food webs.

Neodactylariales, Neodactylariaceae (Dothideomycetes, Ascomycota): new order and family, with a new species from China

During a mycological survey of aquatic hyphomycetes on submerged decaying leaves in southwest China, a distinct new fungus was collected. The collection was cultured and sequenced and a BLAST search of its ITS and LSU sequence against data in GenBank revealed a dothideomycetous affiliation, with the closest related taxa in the genus Neodactylaria. Phylogenetic analyses of a multigene matrix containing sequences from four genes (LSU, SSU, rpb2, and tef1), representing broad groups of Dothideomycetes, revealed its placement within Dothideomycetes, but without a supported familial or ordinal affiliation. Based on further phylogenetic analyses and morphological investigations, the new fungus is described here as a new species of Neodactylaria, N. simaoensissp. nov., and placed in a new family Neodactylariaceaefam. nov. and a new order Neodactylarialesord. nov.