Enough sugar for a fun-gi?

Despite being ecologically successful the marine fungi are often neglected. These fungi can interact pathogenically or mutualistically with both micro- and macro- algae. As such, these fungi tend to have high metabolic rates and rapid growth. The most prevalent forms of fungi in the marine environment are filamentous ascomycetes, that said several basidiomycetes and yeast species flourish. Fungal diversity largely depends on environmental factors such as temperature and salinity. Fungi play an important role in providing nutrition for detritivores, achieved through the breakdown of POM. The high biomass of marine fungi coupled with the high cellular enzyme activity of several substrates recently observed, suggest that microscopic filamentous fungi may play a role in biogeochemical cycles. As such, this paper aimed to address how glucose metabolism (and furthermore heterotrophic activity) changes in accordance with temperature, and discuss the findings within the context of biogeochemistry and ecology.

Samples of seawater and sediment from the coast of Chile were collected, filtered, and cultured on agar (glucose, yeast extract and Emerson’s YpSs agar). Using DNA analysis, the fungal species were identified as, Penicillium decumbens, P. chrysogenum (water column) and Acremonium strictum, Fusarium fujikuroi and F. sporotrichioides (sediment). Each of these species was diluted with an OD concentration of ~0.85, subject to temperatures of 9, 13 and 20°C with 5g L^-1 of glucose, sampled daily for 7 days and  the respiration (respirometer and Optode sensors) and biomass measured using microscopy, epifluorescence and ATP content measured (experiment 1). Growth potential was then assessed with fungi subject glucose concentrations of 0.001, 0.01, 0.1 and 1 g L^-1 (experiment 2).

As anticipated, growth rates were greatest at higher temperatures (20°C) with 55-153 µg C hypha day^-1, growth at 9°C was significantly reduced with 21-51 µg C hypha day^-1 observed. Growth at 13°C was intermediate. Of the five species studied, no significant differences in growth at 0.001 and 0.01 g L^-1 glucose were observed, here carbon biomass reached 0.32 mg C and 0.45 mg C at 9 and 20°C, respectively. Growth of marine fungal species at 9 and 20°C and the four glucose concentrations all showed similar trends, with growth increasing until a plateau at the highest glucose concentration. Generally, oxygen consumption increased with increasing temperature. The variation because of body size was examined by comparing other fungal species, and their relative oxygen consumption; only 2; only 24% of the variation could be accounted for.

This investigation is particularly interesting in the perspective of climate change. The interaction of temperature and oxygen consumption is a fairly well studied subject in marine invertebrates, thus comparing these findings with those for other taxa and discussing these findings in the context of Portner’s aerobic scope hypothesis would be very interesting. As aforementioned in previous posts, all aspects of science need further investigation, however alongside viruses, I think marine fungi need more attention. Their role in biogeochemical cycles, symbioses and nutrient cycling are not known. 

Marcelo E. Fuentes, Renato A. Quiñones, Marcelo H. Gutiérrez, Silvio Pantoja (2014), Effects of temperature and glucose concentration on the growth and respiration of fungal species isolated from a highly productive coastal upwelling ecosystem. Fungal Ecology.13:135-149.