Uphill energy transfer mechanism for photosynthesis in the Antarctic alga

Prasiola crispa, a major green alga in Antarctica, forms layered colonies for survival under the severe terrestrial conditions of Antarctica, which include severe cold, drought, and strong sunlight. As a result of these conditions, the surface cells of P. crispa and other Antarctic organisms face high risk of photodamage. Cells of deeper layer escape from photodamage at the sacrifice of photosynthetic active radiation except infrared. P. crispa achieves effective photosynthesis by low energy far-red light for photosystem II excitation with high efficiency similar to that of visible light. Here, we identified a far-red light-harvesting complex of photosystem II in P. crispa, Pc-frLHC, and proposed a molecular mechanism of uphill excitation energy transfer based on its cryogenic electron-microscopy structure. While Pc-frLHC is associated with photosystem II, it is evolutionarily related to the light-harvesting complex of photosystem I. Pc-frLHC forms a ring-shaped homo-undecamer in which all chlorophyll a molecules are energetically connected and contains chlorophyll a trimers. It seems that the trimers are long-wavelength-absorbing chlorophylls for far-red light at 708 nm, and further absorbance extension is accomplished by Davydov-splitting in dimeric chlorophylls. The chlorophyll network should enable a highly efficient entropy-driven uphill excitation energy transfer using far-red light up to 725 nm.

Biodiversity of periphytic cyanobacteria and algae assemblages in polar region: a case study of the vicinity of Arctowski Polish Antarctic Station (King George Island, Antarctica)

This study was carried out on periphytic cyanobacteria and algae assemblages of microbial mats in streams and small water bodies during the Antarctic summer of 2019 in the vicinity of Ecology Glacier (King George Island, Antarctica). The significantly diversified assemblages between the microbial mats of small water bodies and streams were observed. The higher biomass and proportion of periphytic cyanobacteria with Planktothix agardhii as dominant species were found in the streams at lower mean water temperature and higher nutrient content while diatoms generally dominated in the small water bodies (primarily Fragilaria capucina). Chlorophyta also reached a significant proportion in the total biomass of periphyton with dominant species of Prasiola crispa and Keratococcus mucicola. The growth of periphytic cyanobacteria and algae was determined mainly by type of substrate, water temperature and nutrient concentrations. The results also suggest the phenomenon of nutrient uptake by these assemblages from the waters, confirmed by the negative correlations between some species and nutrients (TN, TP, N-NH4, P-PO4). A large share of commonly occurring periphytic species and limitation of typically polar ones, suggest progressive changes in the eutrophication of Antarctic waters caused by the global climate change and increased pollution in the environment. Therefore, these areas should be subject to a special legal protection, preceded by detailed research of these ecosystems.

Entomotoxic Activity of Prasiola crispa (Antarctic Algae) in Nauphoeta cinerea Cockroaches: Identification of Main Steroidal Compounds

Prasiola crispa is a macroscopic green algae found in abundance in Antarctica ice free areas. Prasiola crispan-hexaneextract (HPC) induced insecticidal activity in Nauphoeta cinerea cockroaches after 24 h of exposure. The chemical analysis of HPC revealed the presence of the followingphytosterols: β-sitosterol, campesterol and stigmasterol. The incubation of cockroach semi-isolated heart preparations with HPC caused a significant negative chronotropic activity in the heartbeats. HPC affected the insect neuromuscular function by inducing a complete inhibition of the cockroach leg-muscle twitch tension. When the isolated phytosterols were injected at in vivo cockroach neuromuscular preparations, there was a progressive inhibition of muscle twitches on the following order of potency: β-sitosterol > campesterol > stigmasterol. HPC also provoked significant behavioral alterations, characterized by the increase or decrease of cockroach grooming activity, depending on the dose assayed. Altogether, the results presented here corroborate the insecticide potential of Prasiola crispa Antarctic algae. They also revealed the presence of phytosterols and the involvement of these steroidal compounds in the entomotoxic activity of the algae, potentially by modulating octopaminergic-cholinergic pathways. Further phytochemical-combined bioguided analysis of the HPC will unveil novel bioactive compounds that might be an accessory to the insecticide activity of the algae.

Natural history of the terrestrial green alga, Prasiola crispa (Trebouxiophyceae), and associated Herring Gulls on Brier Island, Nova Scotia

The local distribution of Prasiola crispa is reported for the first time in Nova Scotia. It was common on emergent basalt outcrops in a coastal wetland on the Bay of Fundy shores of Brier Island. The alga was present on 19 of 102 basalt outcrops in one of the breeding colonies of the Herring Gull, Larus argentatus, and was only associated with basalt outcrops with gull feces. Patches of P. crispa were typically associated with the north facing slopes of the rock or were present in depressions or parts of the rock shaded by adjacent vegetation. At Western Light, the gulls are both facilitating the presence of P. crispa and acting as ecosystem engineers by nesting in the adjoining vegetation where their trampling and nutrient inputs are modifying the surrounding wetland ecosystem.