A Possible Involvement of Sialidase in the Cell Response of the Antarctic Fungus Penicillium griseofulvum P29 to Oxidative Stress

Abstract

Sialidases/neuraminidases remove terminal sialic acid residues from glycoproteins, glycolipids, and oligosaccharides. Our previous research has revealed the distribution of sialidase in non-clinical fungal isolates from different ecological niches, including Antarctica. Fungi adapted to extremely low temperatures possess defense mechanisms necessary for their survival such as the response against oxidative stress. The relationship between oxidative stress and sialidase synthesis has been studied extremely sparsely. The aim of the present study was to investigate the involvement of sialidase in the cell response of the Antarctic strain P. griseofulvum P29 against oxidative stress induced by long- and short-term exposure to low temperatures. The changes in growth temperatures for 120 h (long-term stress) affected biomass accumulation, glucose consumption, sialidase synthesis, and the activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). The short-term temperature downshift (6 h) caused oxidative stress, evidenced by changes in the levels of biomarkers, including lipid peroxidation, oxidatively damaged proteins, and the accumulation of reserve carbohydrates. Simultaneously, a sharp increase in SOD and CAT activity was found, which coincided with a significant increase in sialidase activity. This study marks the first demonstration of increased sialidase activity in filamentous fungi isolated from extreme cold environments as a response to oxidative stress.

Keywords: Antarctica; antioxidant enzymes; cold stress; fungi; oxidative stress biomarkers; sialidase.

Figure 1

Effect of temperature on the growth (A) and glucose uptake (B) of P. griseofulvum P29. Values are the means of three replicates; error bars represent the standard deviation. Temperatures below the optimal caused a statistically significant effect (Tukey’s test p < 0.05) on the growth and glucose uptake (p ≤ 0.05).

Figure 2

The activity of the sialidase (A), SOD (B), and CAT (C) enzymes as a function of growth temperature. Values are the means of three replicates; error bars represent the standard deviation. Growth temperatures cause a statistically significant effect on the enzyme activities (Tukey’s test p ≤ 0.05).

Figure 3

Changes in the carbonyl content in cells exposed to the optimal temperature (■) and transient downshift to 15 °C (●) and 6 °C (▲). Values are the means of three replicates; error bars represent the standard deviation. Decreased temperatures cause a statistically significant increase in oxidatively damaged protein content (Tukey’s test p < 0.05).

Figure 4

MDA content in the fungal cell exposed to the optimal temperature and short-term downshift to 6 or 15 °C. Values are the means of three replicates; error bars represent the standard deviation. Decreased temperatures cause a statistically significant increase in MDA content (Tukey’s test p < 0.05).

Figure 5

Changes in glycogen (A) and trehalose (B) content during cold stress and recovery in P. griseofulvum P29 upon the temperature downshift from the optimal to 15 °C or 6 °C. Values are the means of three replicates; error bars represent the standard deviation. The effect on reserve carbohydrates was significant for the temperature treatment (Tukey’s test p > 0.05).

Figure 6

Changes in the activity levels of SOD (A) and CAT (B) after short-term treatment with the optimal temperature and at the corresponding stress temperatures (6 °C or 15 °C). Values are the means of three replicates; error bars represent the standard deviation. The temperature caused a statistically significant effect on SOD and CAT activity (Tukey, p > 0.05).

Figure 7

Sialidase activity response of P. griseofulvum P29 to a transient decrease in the growth temperature from the optimal to 15 °C or 6 °C. Values are the means of three replicates; error bars represent the standard deviation. The temperature downshift resulted in a statistically significant increase in enzyme activity.