Terrestrial filamentous fungi from Gruta do Catão (São Desidério, Bahia, Northeastern Brazil) show high levels of cellulose degradation

Abstract

Subterranean environments are oligotrophic. However, few studies have investigated the composition and function of their terrestrial mycobiota. This study examined the functional role of filamentous cave fungi in cellulose degradation. Soil samples and dry sediment were collected in the surface epigean environment and two sites in the entrance and twilight zones inside Gruta do Catão in the São Desidério karst area, state of Bahia, Brazil. Fungi were cultured from the samples, and the total organic carbon, culturable microorganisms, and carbon and nitrogen microbial biomasses were estimated. All fungal strains were evaluated for cellulase production in carboxymethylcellulose synthetic medium, and the enzymatic indices were estimated. We observed a significant difference (p 0.05) in physical, chemical, and biological parameters between epigean soil and cave sediments by Tukey's test. We recovered a total of 20 isolates comprising the genera Aspergillus (50.0%), Penicillium (25.0%), Talaromyces (10.0%), Trichoderma (5.0%), Purpureocillium (5.0%) and Scopulariopsis (5.0%). The majority of the isolates (90%) showed cellulolytic activity, which is a higher percentage compared to that normally reported in the literature for sediments. Thus there is a high probability that the filamentous fungi act in nutrient cycling, thereby contributing to the quality and maintenance of the cave ecosystem. These results indicate that parameters such as total organic carbon, biomass, and relative humidity that tend to differ between caves and epigean environments, provide selective pressures for microorganisms that use alternative sources of energy and nutrients.

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

“…Previous study isolated 20 cellulolytic fungal strains from the entrance Zone (7) and the Twilight Zone (13). The fungal strains were morphologically identified (by microscopic analysis) as the following genera: Aspergillus (50.0%), Penicillium (25.0%), Talaromyces (10.0%), Trichoderma (5.0%), Purpureocillium (5.0%) and Scopulariopsis (5.0%) (Paula et al 2016).…”

“…Pioneering study in Catão cave (Brazil) isolated fungal strains and carried out the screening (plaque test) to select cellulolytic enzyme producing strains. From this study, the authors highlighted the great percentage of cellulolytic strains isolated from the subterranean environment in comparison to the surface environment (Paula et al 2016).…”

“…At the laboratory samples were homogenized, sieved (2 mm mesh) and kept in refrigerator at 4.0°C until the analysis. Sampling details can be accessed at Paula et al (2016).…”

“…Classical taxonomic keys were used to assess all isolates genera (Domsch et al 1980, Barnett andHunter 1998). As described by Paula et al (2016), as one step of their characterization, the strains were also pretested to evaluate their cellulolytic activity by the formation of a degradation zone revealed by the addition of a Congo red solution in colonies grown in carboxymethylcellulose plates.…”

“…Subterranean environments such as caves can be considered extreme environments that provide highly specialized niches (engel 2007) but, so far, they have been overlooked regarding its potential for new genetic resources. For this reason, there are few reports assessing the cellulolytic potential of microorganisms from caves (Ogórek et al 2016, Paula et al 2016, Rautela et al 2017). According to lynd et al (2002) in extreme environments, such as caves, microorganisms tend to use a broad range of carbohydrates, probably as a consequence of the small amount of cellulose input combined with the presence of few competing species in these habitats.…”