Abstract
The Arctic and Antarctic regions constitute 14% of the total biosphere. Although they differ in their physiographic characteristics, both are strongly affected by snow and ice cover changes, extreme photoperiods and low temperatures, and are still largely unexplored compared to more accessible sites. This review focuses on microalgae and bacteria from polar marine environments and, in particular, on their physiological and molecular responses to harsh environmental conditions. The data reported in this manuscript show that exposure to cold, increase in CO2 concentration and salinity, high/low light, and/or combination of stressors induce variations in species abundance and distribution for both polar bacteria and microalgae, as well as changes in growth rate and increase in cryoprotective compounds. The use of -omics techniques also allowed to identify specific gene losses and gains which could have contributed to polar environmental adaptation, and metabolic shifts, especially related to lipid metabolism and defence systems, such as the up-regulation of ice binding proteins, chaperones and antioxidant enzymes. However, this review also provides evidence that -omics resources for polar species are still few and several sequences still have unknown functions, highlighting the need to further explore polar environments, the biology and ecology of the inhabiting bacteria and microalgae, and their interactions.
Highlights
Oceans cover more than 70% of the Earth’s surface, and host diversified habitats and adapted organisms
This review focuses on microalgae and bacteria from polar marine environments and, in particular, on their physiological and molecular responses to harsh environmental conditions
Microalgae, for example, need a specific light regime to carry out their physiological processes, which most bacteria do not require, so they are sensitive to the combination of low temperature and seasonality of solar irradiance [14]
Summary
Oceans cover more than 70% of the Earth’s surface, and host diversified habitats and adapted organisms. If microalgae are found mainly distributed in habitats with specific light irradiance differences (e.g., seawater, sea-ice, snow and rock surfaces), bacteria are well established in other environmental matrices, such as sediments, soils and atmosphere, having to cope with different pressures. Arctic and Antarctic regions are similar in that they are strongly affected by snow and ice cover changes and by extreme photoperiods (with periods of total darkness) and low temperatures. Precipitation as there are no major rivers discharging into the Southern Ocean Another difference between the Arctic and Antarctic pelagic ecosystems is the change in light and in surface sea-ice that occurs at a seasonal and annual scale, respectively. Seasonal or annual freezing-melting cycles of large amounts of seawater lead to changes in physical and biogeochemical properties of both surface ocean and sea-ice [26]. In the following paragraphs we discuss the physiological and molecular responses of microalgae and bacteria to environmental constraints in the Arctic and Antarctic marine environments
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