Photosystems must balance between light harvesting to fuel the photosynthetic process for CO2 fixation and mitigating the risk of photodamage due to absorption of light energy in excess. Eukaryotic photosynthetic organisms evolved an array of pigment‐binding proteins called light harvesting complexes constituting the external antenna system in the photosystems, where both light harvesting and activation of photoprotective mechanisms occur. In this work, the balancing role of CP29 and CP26 photosystem II antenna subunits was investigated in Chlamydomonas reinhardtii using CRISPR‐Cas9 technology to obtain single and double mutants depleted of monomeric antennas. Absence of CP26 and CP29 impaired both photosynthetic efficiency and photoprotection: Excitation energy transfer from external antenna to reaction centre was reduced, and state transitions were completely impaired. Moreover, differently from higher plants, photosystem II monomeric antenna proteins resulted to be essential for photoprotective thermal dissipation of excitation energy by nonphotochemical quenching.

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Summary The xanthophyll cycle is the metabolic process by which the carotenoid violaxanthin is de‐epoxidated to zeaxanthin, a xanthophyll with a crucial photoprotective role in higher plants and mosses. The role of zeaxanthin is still unclear in green algae, and a peculiar violaxanthin de‐epoxidating enzyme was found in the model organism Chlamydomonas reinhardtii. Here, we investigated the molecular details and functions of the xanthophyll cycle in the case of Chlorella vulgaris, one of the green algae most considered for industrial cultivation, where resistance to high light stress is a prerequisite for sustainable biomass production. Identification of the violaxanthin de‐epoxidase enzyme in C. vulgaris was performed by genome mining and in vitro analysis of the catalytic activity of the gene product identified. The photoprotective role of zeaxanthin was then investigated in vivo and in isolated pigment‐binding complexes. The results obtained demonstrate the functioning, even though with a different pH sensitivity, of a plant‐like violaxanthin de‐epoxidase enzyme in C. vulgaris. Differently from C. reinhardtii, zeaxanthin accumulation in C. vulgaris was found to be crucial for photoprotective quenching of excitation energy harvested by both photosystem I and II. These findings demonstrate an evolutionary divergence of photoprotective mechanisms among Chlorophyta.

Acute toxicity and genotoxic activity of 11 pollutants were investigated in wild populations of Diamesa cinerella and Diamesa zernyi (Diptera Chironomidae) from two alpine streams (Italian Alps). D. cinerella was collected in two sites on the non-glacial Vermigliana stream, 50 m-upstream and 5-m downstream of the Wastewater Treatment Plant (WTP) at the Tonal Pass (1799 m a.s.l.). D. zernyi was collected in the Presena glacial stream, close to the glacier snout (2685 m a.s.l.). IV-instar larvae were exposed for 24-96 h to increasing concentrations of three drugs (ibuprofen-IBU, furosemide-FUR, trimethoprim-TMP), three personal care products (triclocarban-TCC, tonalid-TON, sucralose-SUCR), and five pesticides (boscalid-BOS, captan-CAP, chlorpyrifos-CPS, metolachlor-MET, terbuthylazine-TER). The experimental concentrations were from one to several million times higher than the highest environmental concentration (EC) measured in the study sites. Two mixtures of pesticides were also prepared: MIX 1K =103 x EC of CPS, MET and TER, and MIX 10K = 104 x EC of CPS, MET and TER. Species- and site-specific responses were observed for both tests. On the basis of survival data, both species resulted very resistant to pharmaceuticals (mainly to FUR for which no effects on survival and movement or pupation were observed), and more sensitive to pesticides (mainly to CPS, MET and CAP). Genotoxicity tests (Comet assay) highlighted a WTP effect under natural conditions and a genotoxic effect for 9 of the 11 tested compounds. Overall, a clear gradient of increasing resistance in larvae from the least (PR0) to the most polluted (TP_dw) site was highlighted by both tests, ecotoxicological and of genotoxicity, as also expected according to species autecology (D. zernyi is restricted to very cold and pristine habitats). D. cinerella living downstream of the effluent accumulates a significantly higher DNA damage than the other populations, highlighting a basal physiological stress condition in nature. It is plausible that these larvae possess chemical resistance strategies to survive already under natural conditions. Diamesa spp. exhibited a higher toxic resistance than any other model species tested to date under the same pollutants, probably associable to its strong cold resistance. The results emphasised that the measured concentrations of Contaminants of Emerging Concern (CECs) and pesticides seem to be far below those required to cause acute effects. However, the effects on freshwater communities of prolonged exposure to mixture of trace CECs and pesticides remain unknown.

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Recently, the use of Daphnia magna has been proposed in on-line and real-time biomonitoring programmes as an early warning system for evaluating the effluent quality of sewage treatment plants (STPs). These systems are based on recording behavioural changes in the test organism resulting from the stress caused by the effluents. Indeed, altered behavioural signals could be induced at sublethal concentrations that are significantly lower than the corresponding EC50. However, at present, it is unknown whether the sensitivity of D. magna can be representative of that of other aquatic organisms, particularly benthic macroinvertebrates. An experiment was designed to verify whether D. magna can be employed in biomonitoring programmes for STPs located in alpine areas as a surrogate for cold freshwater best-adapted species. The responses of survival and behaviour alteration to exposure to the effluent of the Tonale Pass plant (Trentino, Italian Alps, 46°N, 10°E; 1799 m a.s.l.) were compared in a laboratory population of D. magna and a wild population of the chironomid Diamesa cinerella. These larvae were collected from the Vermigliana stream 50 metres upstream of the effluent input. Both organisms were exposed for 24 and 48 hrs to the effluent as it is and to three dilutions (/10, /100, /1000). The mortality rate and behavioural responses (using video tracking systems) were recorded. No significant mortality or change in behaviour was observed in the two species when exposed to the undiluted effluent. Exposure to serial dilutions of the treated effluent did not affect the survival of either species but notably altered their behaviour at both exposure times (e.g., the time spent in activity in D. magna and the average speed of movement and the cumulative distance travelled in both), especially when exposed to the ten-times-diluted effluent. Overall, the findings of this study emphasize that even though D. magna and D. cinerella use different behavioural strategies to cope with adverse environmental conditions, their overall sensitivity to treated effluents is similar. Accordingly, the use of D. magna in biological early warning systems protocols seems to also be sufficiently protective for local, cold-adapted species of alpine freshwater ecosystems.

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Subterranean environments on Earth serve as an analog for the study of microbes on other planets, which has become an active area of research. Although it might sound contradictory that photosynthetic cyanobacteria thrive in extreme low light environments, they are frequent inhabitants of caves on Earth. Throughout the phylum these cyanobacteria have developed unique adaptations that cannot only be used for biotechnological processes but also have implications for astrobiology. They can, for example, both accommodate for the low light conditions by producing specific pigments that allow photosynthesis in near-infrared (IR) radiation/far-red light, and they can synthesize bioplastic compounds and calcium carbonate sheaths which represent valuable resources during human colonization of other planets or rock bodies. This article will highlight the potential benefits of cave-inhabiting cyanobacteria and will present a suitable bioreactor technique for the utilization of these special microbes during future space missions.