Effects of global environmental change on microalgal photosynthesis, growth and their distribution

Effects of temperature on morphology, physiology, and metabolic profile of diazotrophic cyanobacteria inhabiting diverse habitats

Global population expansion has increased the demand for food supply and agricultural productivity. Abiotic stressors like temperature have significantly restricted agriculture in cropland and jeopardized food security. Cyanobacteria play a crucial role in fostering sustainable agriculture and ensuring global food security. In the present study, we have assessed the effect of temperatures on diazotrophic free living rice-field and hot-spring cyanobacteria. They were treated to a variable range of temperatures to see the changes in cellular morphology, physiology, and biochemical characteristics. The rise of temperatures induces growth (60 %), total protein (54 %) contents of rice-field cyanobacterium until 25 °C, further treatment results in decline (20 %) at 45 °C. However, growth indices were increased till 35 °C (90 %) in hot-spring cyanobacterium and further treatment did not exhibit a significant decline in the same. However, the reactive oxygen species (ROS) generation and lipid peroxidation (LPO) were higher in rice-field (2.8 and 1.7 fold) as compared to hot-spring cyanobacterium (2.2 and 1.6 fold). In response to temperature, enzymatic antioxidant contents were much higher in hot-spring as compared to rice-field cyanobacterium. Similarly, carotenoid and carbohydrate content was also higher in hot spring (2 fold) as compared to rice-field cyanobacterium (1.5 and 1.2 fold). All these data collectively suggest that hot-spring (Nostoc sp. strain VKB02) has a higher thermoprotective capacity with novel defense mechanisms as compared to rice-field cyanobacterium (Anabaena sp. strain VKB01). These findings contributed to a better understanding of the temperature stress, improvement of agricultural productivity and future welfare of green ecosystems.

How a constructed wetland within a natural park enhances plankton communities after more than 10 years of operation: Changes over space and time

Constructed wetlands are increasingly used as a solution to treat polluted water in natural environments. Located in the Albufera de València Natural Park, a constructed wetland was built in 2009 as a pilot project to act as an intermediary between low-quality waters and the largest protected coastal lagoon in the Iberian Peninsula. With a unique dataset spanning more than a decade (2009-2023), this study assessed changes in plankton communities both spatially (comparing six sampling sites) and temporally (comparing four periods of years). The results show how the constructed wetland, after nearly 15 years of operation, has not only maintained but also improved its capacity to enhance the biological quality of the water which is released into the protected lagoon, thus fulfilling one of the main aims of its construction. During the last period (2020-2023) of the time series, the constructed wetland outlets had significantly higher zooplankton biomass, particularly filter-feeding cladocerans, compared to the inlets. This clear improvement in the plankton community was due to management interventions (e.g., drying sectors of the constructed wetland during the summers since 2019) and the rise in temperature. These circumstances promoted earlier hatching of cladoceran diapause eggs from the sediments compared to previous years, maintaining their presence throughout all seasons. Consequently, the outlets of the constructed wetland had significantly lower phytoplankton abundance and sestonic chlorophyll-a concentrations than in the past, nearly oligotrophic states, and a reduced biovolume of potentially toxic cyanobacteria in the released waters.

Benzophenone-4 inhibition in marine diatoms: Physiological and molecular perspectives

Benzophenone-4 (BP-4), a widely utilized organic ultraviolet (UV) filter, is recognized as a pseudo-persistent contaminant in aquatic environments. To elucidate the effects and mechanisms of BP-4 on marine diatoms, an investigation was conducted on the growth rate, photosynthetic pigment content, photosynthetic parameters, antioxidant enzyme activity, malondialdehyde (MDA) levels, cellular structure, and transcriptome profile of the model species, Phaeodactylum tricornutum. The results showed a pronounced inhibition of algal growth upon exposure to BP-4, with a 144 h-EC50 value of 201 mg·L-1. In addition, BP-4 exposure resulted in a significant reduction in biomass, disruption of cell membrane integrity, and increased MDA accumulation, with levels escalating 3.57-fold at 125 mg·L-1 of BP-4. In the BP-4-treated samples, 1556 differentially expressed genes (DEGs) were identified, of which 985 were upregulated and 571 were downregulated. Gene ontology and KEGG pathway enrichment analysis revealed that the carbon fixation and carbon metabolism processes in P. tricornatum were disrupted in response to BP-4 exposure, along with excessive reactive oxygen species (ROS) production. The upregulation of genes associated with photosynthetic pigment (chlorophyll and carotenoids) synthesis, phospholipid synthesis, ribosome biogenesis, and translation-related pathways may be regarded as a component of P. tricornatum's tolerance mechanism towards BP-4. These results provide preliminary insights into the toxicity and tolerance mechanisms of BP-4 on P. tricornatum. They will contribute to a better understanding of the ecotoxicological impacts of BP-4 on the marine ecosystem and provide valuable information for elimination of BP-4 in aquatic environment by bioremediation.

Sub-pilot scale sequential microalgal consortium-based cultivation for treatment of municipal wastewater and biomass production

Municipal wastewater (MWW) was treated by a sequential pilot microalgal cultivation process. The cultivation was performed inside a specifically designed low-cost photobioreactor (PBR) system. A microalgal consortium 2:1 was developed using Tetraselmis indica (TS) and Picochlorum sp. (PC) in the first stage and PC:TS (2:1) in the second stage and the nutrient removal efficiency and biomass production and biomolecules production was evaluated and also compared with monoculture in a two-stage sequential cultivation system. This study also investigated the effect of seasonal variations on microalgae growth and MWW treatment. The results showed that mixed microalgal consortium (TS:PC) had higher nutrient removal efficiency, with chemical oxygen demand (COD), total phosphate (TP), and total nitrate (TN) removal efficiencies of 78.50, 84.49, and 84.20%, respectively, and produced a biomass of 2.50 g/L with lipid content of 37.36% in the first stage of cultivation under indoor conditions. In the second stage of indoor cultivation, the PC:TS consortium demonstrated maximum COD, TP, and TN removal efficiencies of 92.49, 94.24, and 94.16%, respectively. It also produced a biomass of 2.65 g/L with a lipid content of 40.67%. Among all the seasonal variations, mass flow analysis indicated that the combination of mixed consortium-based two-stage sequential process during the winter season favored maximum nutrient removal efficiency of TN i.e. 88.54% (84.12 mg/L) and TP i.e., 90.18% (43.29 mg/L), respectively. It also enhanced total biomass production of 49.10 g in 20-L medium, which includes lipid yield ∼15.68 g compared to monoculture i.e., 82.06% (78.70 mg/L) and 82.87% (40.26 mg/L) removal of TN and TP, respectively, and produced biomass 43.60 g with 11.90 g of lipids.

A critical review of soil algae as a crucial soil biological component of high ecological and economic significance

Aero-terrestrial algae are ecologically and economically valuable bioresources contributing to carbon sequestration, sustenance of soil health, and fertility. Compared to aquatic algae, the literature on subaerial algae is minimal, including studies of distinctive habitats such as forest soils, agricultural fields, deserts, polar regions, specific subaerial zones, artificial structures, and tropical soils. The primary goal here was to identify the gaps and scope of research on such algae. Accordingly, the literature was analyzed per sub-themes, such as the "nature of current research data on terrestrial algae," "methodological approaches," "diversity," "environmental relationships," "ecological roles," and "economic significance." The review showed there is a high diversity of algae in soils, especially members belonging to the Cyanophyta (Cyanobacteria) and Chlorophyta. Algal distributions in terrestrial environments depend on the microhabitat conditions, and many species of soil algae are sensitive to specific soil conditions. The ecological significance of soil algae includes primary production, the release of biochemical stimulants and plant growth promoters into soils, nitrogen fixation, solubilization of minerals, and the enhancement and maintenance of soil fertility. Since aero-terrestrial habitats are generally stressed environments, algae of such environments can be rich in rare metabolites and natural products. For example, epilithic soil algae use wet adhesive molecules to fix them firmly on the substratum. Exploring the ecological roles and economic utility of soil and other subaerial algae could be helpful for the development of algae-based industries and for achieving sustainable soil management.

Evaluation of short-term copper toxicity in a co-culture of Synechococcus sp., Chaetoceros gracilis and Pleurochrisys cf. roscoffensis exposed to changes in temperature and salinity levels

Metals such as copper (Cu) enter marine environments from natural and anthropogenic sources, causing changes in the biodiversity of marine microalgae and cyanobacteria. Cu plays a dual role as either a micronutrient or toxicant depending on the environmental concentration. Many studies have summarized the potential of Cu to become more toxic to microalgae under environmental stress (for instance climate change). Most of the data available on Cu toxicity concerning microalgae and cyanobacteria have been produced using single-species laboratory tests, and there is still a significant gap in the information concerning the behavior of a group of algae exposed to environmental stressors. Thus, the objective of this study was to evaluate the toxicity of Cu at two concentrations (C1 = 2 μg L-1 and C2 = 5 μg L-1) in multispecies bioassays using three phytoplankton species (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis and Pleurochrisys cf. roscoffensis). Combinations of two temperatures (20 and 23 °C) and two salinities (33 and 36 PSU), were applied in a 96 h study using flow cytometry analysis (FCM). Algal growth and reactive oxygen species (ROS) production by 2'7'-dichlorofluorescein (DCFH) were monitored by FCM. The results indicated that Synechococcus sp. was more sensitive than C. gracilis and P. roscoffensis to Cu stress at a temperature 23 °C and salinity of 36 PSU under both concentrations of Cu. Chlorophyll a fluorescence showed a significant decrease (p < 0.05) in Synechococcus sp. under 5 μg L-1 of Cu in the combined treatment of 20 °C and 33 PSU; however, there was a significant increase in P. roscoffensis in all combinations at C2 = 5 μg L-1 compared to the control with no Cu, indicating a potential hormetic response to Cu for P. roscoffensis. ROS levels were triggered in a combination of 23 °C and 33 PSU and 5 μg L-1 of Cu, which was higher than all the other combinations studied. Our study resulted in data concerning the potential impacts caused by possible future climate change scenarios in aquatic habitats chronically exposed to metals.

Population and functional changes in a multispecies co-culture of marine microalgae and cyanobacteria under a combination of different salinity and temperature levels

Changes in the temperature or salinity of ocean waters can affect marine organisms at multiple trophic levels. Both environmental variables could have an impact on marine microalgae populations. Therefore, the effect of the combination of three levels of temperature (20, 24 and 28 °C), and three levels of salinity (33, 36, and 39 PSU) were evaluated on the growth of a multispecies community of five common species of phytoplankton: (one cyanobacteria, Synechococcus sp., and four microalgae, Chaetoceros gracilis, Amphidinium carterae, Pleurochrysis roscoffensis and Rhodomonas baltica). The co-culture was monitored by flow cytometry under controlled conditions in a 96 h study. The effect of both variables on dissolved oxygen concentrations was measured using the SDR SensorDish Reader system. The results demonstrated that Synechococcus sp., C. gracilis, and A. carterae displayed a high growth at the temperature of 28 °C combined with the lowest salinity assayed. However, salinity increases negatively affected the growth of P. roscoffensis and R. baltica. Decreased salinity combined with decreased temperature exhibited a higher net O2 production. The interaction of two environmental factors related to global change such as temperature and salinity can cause structural (community growth) and functional (net oxygen production) changes in a phytoplanktonic community.

Proline, Cysteine and Branched-Chain Amino Acids in Abiotic Stress Response of Land Plants and Microalgae

Proteinogenic amino acids are the building blocks of protein, and plants synthesize all of them. In addition to their importance in plant growth and development, growing evidence underlines the central role played by amino acids and their derivatives in regulating several pathways involved in biotic and abiotic stress responses. In the present review, we illustrate (i) the role of amino acids as an energy source capable of replacing sugars as electron donors to the mitochondrial electron transport chain and (ii) the role of amino acids as precursors of osmolytes as well as (iii) precursors of secondary metabolites. Among the amino acids involved in drought stress response, proline and cysteine play a special role. Besides the large proline accumulation occurring in response to drought stress, proline can export reducing equivalents to sink tissues and organs, and the production of H2S deriving from the metabolism of cysteine can mediate post-translational modifications that target protein cysteines themselves. Although our general understanding of microalgae stress physiology is still fragmentary, a general overview of how unicellular photosynthetic organisms deal with salt stress is also provided because of the growing interest in microalgae in applied sciences.

The Impact of Viral Infection on the Chemistries of the Earth's Most Abundant Photosynthesizes: Metabolically Talented Aquatic Cyanobacteria

Cyanobacteria are the most abundant photosynthesizers on earth, and as such, they play a central role in marine metabolite generation, ocean nutrient cycling, and the control of planetary oxygen generation. Cyanobacteriophage infection exerts control on all of these critical processes of the planet, with the phage-ported homologs of genes linked to photosynthesis, catabolism, and secondary metabolism (marine metabolite generation). Here, we analyze the 153 fully sequenced cyanophages from the National Center for Biotechnology Information (NCBI) database and the 45 auxiliary metabolic genes (AMGs) that they deliver into their hosts. Most of these AMGs are homologs of those found within cyanobacteria and play a key role in cyanobacterial metabolism-encoding proteins involved in photosynthesis, central carbon metabolism, phosphate metabolism, methylation, and cellular regulation. A greater understanding of cyanobacteriophage infection will pave the way to a better understanding of carbon fixation and nutrient cycling, as well as provide new tools for synthetic biology and alternative approaches for the use of cyanobacteria in biotechnology and sustainable manufacturing.

Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria

Global Climate Change could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study the effect of combination of three levels of temperature (20, 23, and 26 °C), and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (39 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, the but highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.