Nedelina Kostadinova

Antioxidant enzyme activity of filamentous fungi isolated from Livingston Island, Maritime Antarctica

From 18 soil samples taken in the vicinity of the permanent Bulgarian Antarctic base “St. Kliment Ohridski” (62°38′29″S, 60°21′53″W) on Livingston Island, 109 filamentous fungi were isolated on selective media. The most widespread fungal species were members of the genera Cladosporium, Geomyces, Penicillium and Aspergillus. Other species, already recorded in Antarctic environment, were also isolated: Lecanicillium muscarium, Epicoccum nigrum and Alternaria alternata. Thirty strains demonstrating good growth were screened for antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) that play an important role in the defense of aerobic organisms against oxidative stress, by converting reactive oxygen species into nontoxic molecules. Six of them showed high enzyme activity. The tested strains produced SOD with statistically significant higher activity at 15°C than at 30°C suggesting that this enzyme is cold-active. Such SOD could be useful in medicine and cosmetics. The best producer of cold-active SOD, Aspergillus glaucus 363, cultivated in bioreactors, demonstrated optimal growth temperature at 25°C and maximum enzyme activities at 25 and 30°C for SOD and CAT, respectively. The electrophoretical analysis showed that the fungus possesses Cu/Zn-SOD.

Isolation and Identification of Filamentous Fungi from Island Livingston, Antarctica

ABSTRACT Over the last decades, the Antarctic regions have been investigated mainly for the presence and exploitation of psychrophilic bacteria and archea, occasionally for algae and more rarely for fungi. The present study reports results concerning the isolation and identification of filamentous fungi from samples of soil taken from Livingston Island, South Shetland Archipelago, West Antarctica. Using conventional media and techniques, all collection sites yielded populations of filamentous fungi, belonging to the phylum Ascomycota (7 genera), Deuteromycota (2), Zygomycota (2) and Basidiomycota (1). Mucor, Cladosporium, Alternaria, Aspergillus and Penicillium were predominant genera. Lecanicillium, Botrytis, Geomyces, Monodictys and Rhizopus were the most frequently isolated genera. Most of the fungal isolates proved to be cold-tolerant

Cold Stress in Antarctic Fungi Targets Enzymes of the Glycolytic Pathway and Tricarboxylic Acid Cycle

ABSTRACT To evaluate the concept of metabolic cold adaptation in Antarctic fungi, we compared the activities of several key enzymes of the glycolytic pathway and the TCA cycle (hexokinase, glucose-6-phosphate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, succinate dehydrogenase, isocitrate dehydrogenase, and malate dehydrogenase) in psychrotolerant Penicillium sp. 161 and mesophilic Aspergillus glaucus 363 during both the stress exposure (6 h) and recovery phases. Mycelia of the Antarctic strains, grown until middle exponential phase at optimal temperature, were shifted to colder temperatures, i.e., 4 and 10°C. Our investigations showed a re-routing of carbon metabolism away from glycolysis into the pentose phosphate pathway (PPP), which serves as a cellular stress-resistance mechanism under cold stress conditions. Moreover, the data clearly suggest strain-dependent differences in cold stress response concerning TCA enzyme activities between both fungi. The psychrotolerant strain induces glyoxalate cycle activities and the mesophilic strain uses a reduction of respiratory activity. A recovery response after removal of the stress factor was observed.

Transient Cold Shock Induces Oxidative Stress Events in Antarctic Fungi

The Antarctic biota has evolved under the influence of a suite of geological and climatic factors, including the geographic isolation of the landmass and the continental shelves, extremely low temperatures and intense seasonality (Russo et al., 2010). The isolation and environmental history of Antarctica have led to a unique biota. Many groups of organisms became extinct in Antarctica as a result of the extremely cold conditions. Although this continent is the coldest, highest, windiest, driest, wildest and most pristine of all of the continents, it is full of life. In addition to its well-known inhabitants, such as penguins and seals, it also has a diverse and unique range of microbial diversity (Nichols et al., 1999; Vincent, 2000). Microorganisms successfully colonise cold habitats and play a major role in the processes of nutrient turnover at low temperatures. In recent years, a growing attention in research has been devoted to cold-adapted microorganisms. This interest in Antarctic microorganisms stems from several reasons. Antarctica’s environmental extremes present conditions in which microorganisms have evolved unique characteristics for survival, which are of great scientific interest. Moreover, the availability of novel Antarctic species, which are generally isolated from extreme environments, opens the door for biotechnological exploration. Investigations of psychrotolerant and psychrophilic microorganisms are also important for human health because microorganisms can cause food spoilage and food-borne diseases. Research on cold shock raises a number of questions: which cellular function is affected most upon cold shock, what makes cell growth stop, and are there well-conserved or common cold shock proteins as in the case of heat-shock proteins? These questions are no less important than those in the case of heat shock (Inouye, 1999).

Potential of ligninolytic enzymatic complex produced by white-rot fungi from genus Trametes isolated from Bulgarian forest soil

Because of the crucial role of ligninolytic enzymes in a variety of industrial processes, the demand for a new effective producer has been constantly increasing. Furthermore, information on enzyme synthesis by autochthonous fungal strains is very seldom found. Two fungal strains producing ligninolytic enzymes were isolated from Bulgarian forest soil. They were identified as being Trametes trogii and T. hirsuta. These two strains were assessed for their enzyme activities, laccase (Lac), lignin peroxidase (LiP) and Mn‐dependent peroxidase (MnP) in culture filtrate depending on the temperature and the type of nutrient medium. T. trogii was selected as the better producer of ligninolytic enzymes. The production process was further improved by optimizing a number of parameters such as incubation time, type of cultivation, volume ratio of medium/air, inoculum size and the addition of inducers. The maximum activities of enzymes synthesized by T. trogii was detected as 11100 U/L for Lac, 2.5 U/L for LiP and 4.5 U/L for MnP after 14 days of incubation at 25°C under static conditions, volume ratio of medium/air 1:6, and 3 plugs as inoculum. Among the supplements tested, 5% glycerol increased Lac activity to a significant extent. The addition of 1% veratryl alcohol had a positive effect on MnP.