# Cell Response to Oxidative Stress in Antarctic Filamentous Fungi
## 6 Low Temperature-Induced Oxidative Stress in Antarctic Fungi
At lower temperatures, there is an increased production of long-chain polyunsaturated fatty acids (LCPUFAs), including eicosapentaenoic, arachidonic, and docosahexanenoic acids [179]. These compounds form hydrophobic boundaries between lipid bilayers, thereby preventing ROS damage and the intake of H\({}_{2}\)O\({}_{2}\) into cells. Consequently, LCPUFAs have been identified as playing a crucial role in the protection of cells from oxidative stress under these lower temperature conditions. Moreover, the shortening of fatty acid chain lengths has been detected as a response to cold stress [180]. Changes in lipids are significantly associated with the stability of membrane structures in fungi and their integrity under low-temperature conditions [154]. The authors found a decreased phospholipid metabolism in the Antarctic isolate _Pseudogymnoascus_ spp. (sp3) in response to cold stress. The Antarctic strain of _Geomyces Pamorum_ exhibited enhanced membrane fluidity due to alterations in the phospholipid composition of its membrane lipids when exposed to low temperatures [181]. Sterols serve an essential structural and regulatory function within eukaryotic cell membranes, affecting their fluidity. They intercalate within the fatty acid chains, generally contributing to the stabilization and fortification of the membrane lipid bilayer [180]. Using transcriptomic analysis, [PERSON] et al. [182] demonstrated an up-regulation of genes associated with the biosynthesis of unsaturated fatty acids in _Mrakia psychrophile_ grown at 4 \({}^{\circ}\)C. This suggests that the cold adaptation mechanism of the obligatory psychrophile fungus involves the synthesis of unsaturated fatty acids to preserve membrane fluidity. Data on the fungus _Thermomyces dupontii_ revealed a lipid-mediated fungal response to cold stress [183]. In the context of low-temperature stress, cold-adapted fungi demonstrated significant damage in the tertiary structures of molecules such as enzymes and other functional proteins, which compromise their functionality and may lead to degradation. Similar data on the cold stress response of fungi isolated from Antarctica are described in previous publications of our group. Research demonstrated that protein carbonyls serve as reliable biomarkers for evaluating protein oxidation, which is a consequence of temperature stress. The long-term growth of Antarctic strains _P. olsonii_ p14 and _P. waksmanii_ m12, along with the temperate strain _Penicillium_ sp. t35, under suboptimal temperature conditions, resulted in a significant increase in protein carbonyl concentrations [87]. A six-hour temperature downshift applied to exponentially growing cultures of these strains led to an observable increase in the number of carbonyl groups in cell proteins throughout the entire period. The mesophilic strains (_P. waksmanii_ m12 and _Penicillium_ sp. t35) exhibited a more substantial increase in the content of damaged proteins compared to the psychrotolerant strain (_P. olsonii_ p14) [170]. Thus, the cold-adapted Antarctic psychrotolerant strain showed enhanced tolerance to cold stress in contrast to the mesophilic strains. The stationary-phase cultures also demonstrated a remarkable increase in carbonylated protein content, but to a greater extent [52]. It could be assumed that the exponential-phase cells exhibit higher resistance to cold stress. A remarkable increase in carbonylated protein content has also been evaluated in two Antarctic strains, particularly the psychrotolerant _Penicillium_ sp. 161 and mesophilic _A. glaucus_ 363, when subjected to temperatures of 4 \({}^{\circ}\)C or 10 \({}^{\circ}\)C [163]. The same typical response to oxidative stress regarding protein damage by low-temperature exposure has been reported for _P. griseafulvum_[171; 176]. The modification of DNA is also significant in understanding the interplay between low temperatures and oxidative stress. Cells may either accumulate DNA molecules that have been damaged by reactive oxygen species (ROS) or successfully repair them to their original state [184].