High cellulolytic activities in filamentous fungi isolated from an extreme oligotrophic subterranean environment (Catão cave) in Brazil.

Isolation and screening of new fungal strains from extreme and understudied environments, such as caves, is a promising approach to find higher yields enzyme producers. Cellulolytic fungal strains isolated from a Brazilian cave were evaluated for their enzymatic production after submerged (SmF) and solid-state fermentation (SSF). After SmF, three strains were selected for their high enzymatic activities: Aspergillus ustus for endoglucanase (4.76 U/mg), Talaromyces bruneus for ß-glucosidase (11.71 U/mg) and Aspergillus sp. (CBMAI 1926) for total cellulase (1.70 U/mg). After SSF, these strains, showed better yields compared to the reference strain Aspergillus niger 3T5B8. Aspergillus sp. (CBMAI 1926) stood out as a new species that expressed activity of total cellulases (0.10 U/mg) and low protein concentration (0.44 mg/mL). In conclusion, these isolated strains have a more efficient and promising cellulolytic enzyme complex that can be used in fermentation and saccharification processes with a lower protein concentration and a higher enzymatic activity than the reference strain. Therefore, beside the new genetic material characterized, our study highlights the benefits of cave extreme environments exploitation to find new potentially valuable strains.

Bacterial microbiomes from vertically transmitted fungal inocula of the leaf-cutting ant Atta texana.

Microbiome surveys provide clues for the functional roles of symbiotic microbial communities and their hosts. In this study, we elucidated bacterial microbiomes associated with the vertically transmitted fungal inocula (pellets) used by foundress queens of the leaf-cutting ant Atta texana as starter-cultures for new gardens. As reference microbiomes, we also surveyed bacterial microbiomes of foundress queens, gardens and brood of incipient nests. Pseudomonas, Acinetobacter, Propionibacterium and Corynebacterium were consistently present in high abundance in microbiomes. Some pellet and ant samples contained abundant bacteria from an Entomoplasmatales-clade, and a separate PCR-based survey of Entomoplasmatales bacteria in eight attine ant-genera from Brazil placed these bacteria in a monophyletic clade within the bacterial genus Mesoplasma. The attine ant-Mesoplasma association parallels a similar association between a closely related, monophyletic Entomoplasmatales-clade and army ants. Of thirteen A. texana nests surveyed, three nests with exceptionally high Mesoplasma abundance died, whereas the other nests survived. It is unclear whether Mesoplasma was the primary cause of mortality, or Mesoplasma became abundant in moribund nests for non-pathogenic reasons. However, the consistent and geographically widespread presence of Mesoplasma suggests an important functional role in the association with attine ants.

Marine-derived fungus Aspergillus cf. tubingensis LAMAI 31: a new genetic resource for xylanase production.

Marine-derived fungi have been reported as relevant producers of enzymes, which can have different properties in comparison with their terrestrial counterparts. The aim of the present study was to select from a collection of 493 marine-derived fungi the best producer of xylanase in order to evaluate the enzymatic production under different conditions. A total of 112 isolates produced xylanase in solid medium containing xylan as the carbon source, with 31 of them able to produce at least 10 U/mL of the enzyme. The best production (49.41 U/mL) was achieved by the strain LAMAI 31, identified as Aspergillus cf. tubingensis. After confirming the lack of pathogenicity (absence of ochratoxin A and fumonisin B2 production) this fungus was submitted to the experimental design in order to evaluate the effect of different variables on the enzymatic production, with the aim of optimizing culture conditions. Three experimental designs (two Plackett-Burman and one factorial fractional) were applied. The best condition for the enzymatic production was defined, resulting in an increase of 12.7 times in comparison with the initial production during the screening experiments. In the validation assay, the peak of xylanase production (561.59 U/mL) was obtained after 96 h of incubation, being the best specific activity achieved after 72 h of incubation. Xylanase from A. cf. tubingensis LAMAI 31 had optimum pH and temperature at 5.0 and 55 °C, respectively, and was shown to be stable at a range of 40-50 °C, and in pH from 3.6 to 7.0. Results from the present work indicate that A. cf. tubingensis LAMAI 31 can be considered as a new genetic resource for xylanase production.

New light on the systematics of fungi associated with attine ant gardens and the description of Escovopsis kreiselii sp. nov.

Since the formal description of fungi in the genus Escovopsis in 1990, only a few studies have focused on the systematics of this group. For more than two decades, only two Escovopsis species were described; however, in 2013, three additional Escovopsis species were formally described along with the genus Escovopsioides, both found exclusively in attine ant gardens. During a survey for Escovopsis species in gardens of the lower attine ant Mycetophylax morschi in Brazil, we found four strains belonging to the pink-colored Escovopsis clade. Careful examination of these strains revealed significant morphological differences when compared to previously described species of Escovopsis and Escovopsioides. Based on the type of conidiogenesis (sympodial), as well as morphology of conidiogenous cells (percurrent), non-vesiculated conidiophores, and DNA sequences, we describe the four new strains as a new species, Escovopsis kreiselii sp. nov. Phylogenetic analyses using three nuclear markers (Large subunit RNA; translation elongation factor 1-alpha; and internal transcribed spacer) from the new strains as well as available sequences in public databases confirmed that all known fungi infecting attine ant gardens comprise a monophyletic group within the Hypocreaceae family, with very diverse morphological characteristics. Specifically, Escovopsis kreiselii is likely associated with gardens of lower-attine ants and its pathogenicity remains uncertain.

Broad Escovopsis-inhibition activity of Pseudonocardia associated with Trachymyrmex ants.

Attine ants maintain an association with antibiotic-producing Actinobacteria found on their integuments. Evidence supports these bacteria as auxiliary symbionts that help ants to defend the fungus gardens against pathogens. Using Pseudonocardia strains isolated from Trachymyrmex ants, we tested whether the inhibitory capabilities of such strains are restricted to Escovopsis parasites that infect gardens of this ant genus. Twelve Pseudonocardia strains were tested in in vitro bioassays against Escovopsis strains derived from fungus gardens of Trachymyrmex (n = 1) and leaf-cutting ants (n = 3). Overall, significant differences were observed in the mycelial growth among each Escovopsis strain in the presence of Pseudonocardia. Particularly, Escovopsis from Acromyrmex and Trachymyrmex were the most inhibited strains in comparison to Escovopsis isolated from Atta. This result suggests that Pseudonocardia isolated from Trachymyrmex possibly secrete antimicrobial compounds effective against diverse Escovopsis strains. The fact that Trachymyrmex ants harbour Pseudonocardia strains with broad spectrum of activity and its defensive role on attine gardens are discussed.

Starmerella aceti f.a., sp. nov., an ascomycetous yeast species isolated from fungus garden of the leafcutter ant Acromyrmex balzani.

A novel yeast species was recovered from the fungus garden of the leaf-cutting ant Acromyrmex balzani (Hymenoptera: Formicidae). The growth of the novel yeast species is limited by its ability to metabolize only a few carbon and nitrogenous compounds. A remarkable characteristic of this strain is the vigorous growth in 1 % acetic acid. Sequence analysis of the D1/D2 domains of the LSU rRNA gene showed that the novel species belongs to the Starmerella clade and is phenotypically and genetically divergent from currently recognized species in this clade. Described here as Starmerella aceti f.a., sp. nov., it differs by 37 nucleotide substitutions in the D1/D2 region from Starmerella jinningensis CBS 11864(T), the most closely related species. The type strain of Starmerella aceti sp. nov. is TO 125(T) ( = CBMAI 1594(T) = CBS 13086(T)).