The Role of Microalgae in the Biogeochemical Cycling of Methylmercury (MeHg) in Aquatic Environments

Methylmercury (MeHg) is the most important and the most abundant organic Hg pollutant in the aquatic ecosystem that can affect human health through biomagnification. It is the most toxic organic Hg form, which occurs naturally and by human-induced contamination in water and is further biomagnified in the aquatic food web. MeHg is the only Hg form that accumulates in living organisms and is able to cross the blood–brain barrier, presenting an enormous health risk. Anthropogenic activity increases eutrophication of coastal waters worldwide, which promotes algae blooms. Microalgae, as primary producers, are especially sensitive to MeHg exposure in water and are an important entrance point for MeHg into the aquatic food web. MeHg assimilated by microalgae is further transferred to fish, wildlife and, eventually, humans as final consumers. MeHg biomagnifies and bioaccumulates in living organisms and has serious negative health effects on humans, especially newborns and children. Knowledge of the microalgae–MeHg interaction at the bottom of the food web provides key insights into the control and prevention of MeHg exposure in humans and wildlife. This review aims to summarize recent findings in the literature on the microalgae–MeHg interaction, which can be used to predict MeHg transfer and toxicity in the aquatic food webThis research was funded by the Spanish Ministry of Economic Transformation, Industry, Knowledge and Universities; by the European Regional Development Fund (FEDER) within the framework of the FEDER program of Andalusia (Spain) 2014–2020, grant number UHU–202065; and by Grant P20-00930 from the Andalusian Plan for Research, Development and Innovation, within the frame of the operational program “FEDER Andalucía 2014–2020” The authors wish to thank Erik Björn from Department of Chemistry, Umeå University, Sweden, for his constructive comments on the paper’s content. We wish to thank personnel from LICAH (Laboratorio de Investigación y Control Agroalimentario), University of Huelva, for their collaboration and cooperation under FEDER 2014–2020 UHU–202065 project. We also want to thank colleagues from BITAL (Algae Biotechnology Group), University of Huelva, for their kind assistance in the lab and for creating a productive working environmen

Effect of abiotic stress on the production on lutein and beta-carotene by Chlamydomonas acidophila

Chlamydomonas acidophila growing autotrophically with continuous PAR light (160 µE.m-2.s-1) and 30 ºC may accumulate carotenoids which increase in response to abiotic stress, like high light intensity, UV-A radiation and temperature fluctuation. At 240 µE.m-2.s-1 the alga contains 57.5 ± 1.6 mg.l-1 of total carotenoids after 20 days of growing, which does not significantly change by an irradiance of 1000 µE.m-2.s-1. Lutein (20 ± 0.5 mg.l-1) and β-carotene (8.3 ± 0.2 mg.l-1) production were particularly high in C. acidophila, while zeaxanthine (0.2 ± 0.1 mg.l-1) was low. Enhanced production of these carotenoids was also observed in cultures illuminated with PAR light (160 µE.m-2.s-1) supplemented with moderate UV-A radiation (10 µE.m-2.s-1). Optimum algae growth takes place at 40 ºC, like the maximum amount of intracellular lutein and β-carotene. On the other hand, the presence of iron in the culture medium, in a range between 5-35 mM, significantly decreased the cell viability and the intracellular content of carotenoids, however cupper, at 1-5 mM, appears to increase the synthesis of β-carotene. The alga can growth under mixotrophic conditions, with glucose or acetate, 10 mM, as carbon source, but such conditions did not improved the intracellular content of carotenoids

Interaction of Naturally Occurring Phytoplankton with the Biogeochemical Cycling of Mercury in Aquatic Environments and Its Effects on Global Hg Pollution and Public Health

The biogeochemical cycling of mercury in aquatic environments is a complex process driven by various factors, such as ambient temperature, seasonal variations, methylating bacteria activity, dissolved oxygen levels, and Hg interaction with dissolved organic matter (DOM). As a consequence, part of the Hg contamination from anthropogenic activity that was buried in sediments is reinserted into water columns mainly in highly toxic organic Hg forms (methylmercury, dimethylmercury, etc.). This is especially prominent in the coastal shallow waters of industrial regions worldwide. The main entrance point of these highly toxic Hg forms in the aquatic food web is the naturally occurring phytoplankton. Hg availability, intake, effect on population size, cell toxicity, eventual biotransformation, and intracellular stability in phytoplankton are of the greatest importance for human health, having in mind that such Hg incorporated inside the phytoplankton cells due to biomagnification effects eventually ends up in aquatic wildlife, fish, seafood, and in the human diet. This review summarizes recent findings on the topic of organic Hg form interaction with natural phytoplankton and offers new insight into the matter with possible directions of future research for the prevention of Hg biomagnification in the scope of climate change and global pollution increase scenarios.This research was funded by the Spanish Ministry of Economic Transformation, Industry, Knowledge and Universities; by the European Regional Development Fund (FEDER) within the framework of the FEDER program of Andalusia (Spain) 2014–2020 (grant number: UHU–202065); and by grant P20-00930 from the Andalusian Plan for Research, Development and Innovation, within the frame of the operational program “FEDER Andalucía 2014–2020”. The work of S.S. was supported by project number FCH-S-23-8330 of the Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

Adaptation strategies of endolithic chlorophototrophs to survive the hyperarid and extreme solar radiation environment of the Atacama Desert

The Atacama Desert, northern Chile, is one of the driest deserts on Earth and, as such, a natural laboratory to explore the limits of life and the strategies evolved by microorganisms to adapt to extreme environments. Here we report the exceptional adaptation strategies of chlorophototrophic and eukaryotic algae, and chlorophototrophic and prokaryotic cyanobacteria to the hyperarid and extremely high solar radiation conditions occurring in this desert. Our approach combined several microscopy techniques, spectroscopic analytical methods, and molecular analyses. We found that the major adaptation strategy was to avoid the extreme environmental conditions by colonizing cryptoendolithic, as well as, hypoendolithic habitats within gypsum deposits. The cryptoendolithic colonization occurred a few millimeters beneath the gypsum surface and showed a succession of organized horizons of algae and cyanobacteria, which has never been reported for endolithic microbial communities. The presence of cyanobacteria beneath the algal layer, in close contact with sepiolite inclusions, and their hypoendolithic colonization suggest that occasional liquid water might persist within these sub-microhabitats. We also identified the presence of abundant carotenoids in the upper cryptoendolithic algal habitat and scytonemin in the cyanobacteria hypoendolithic habitat. This study illustrates that successful lithobiontic microbial colonization at the limit for microbial life is the result of a combination of adaptive strategies to avoid excess solar irradiance and extreme evapotranspiration rates, taking advantage of the complex structural and mineralogical characteristics of gypsum deposits—conceptually called “rock's habitable architecture.” Additionally, self-protection by synthesis and accumulation of secondary metabolites likely produces a shielding effect that prevents photoinhibition and lethal photooxidative damage to the chlorophototrophs, representing another level of adaptation. [This Document is Protected by copyright and was first published by Frontiers. All rights reserved. it is reproduced with permission.]CA, JD, OA, AD, and JW are thankful for financial support by CGL2013-42509P grant from MINECO, Spain. JD acknowledges funding from the NASA Exobiology Program (Grant EXOB08-0033) and from the National Science Foundation (Grant NSF-0918907), PV acknowledges funding from the Czech Science Foundation, project no. P210/12/P330 and ENVIMET project CZ.1.07/2.3.00/20.0246 and AD acknowledges funding from the NASA Exobiology Program (Grant NNX12AD61G) and the NASA Astrobiology Institute (NAI Grant NNX15BB01A to the SETT Institute). The authors would like to thank to the MNCN - CSIC Microscopy Service staff and A. Gonzalez (GIG - Univ. Granada) for technical assistance

Haloferax mediterranei Cells as C50 Carotenoid Factories

Haloarchaea produce C50 carotenoids such as bacterioruberin, which are of biotechnological in-terest. This study aimed to analyze the effect of different environmental and nutritional conditions on the cellular growth and dynamics of carotenoids accumulation in Haloferax mediterranei. The maximum production of carotenoids (40 µg·mL−1) was obtained during the stationary phase of growth, probably due to nutrient-limiting conditions (one-step culture). By seven days of culture, 1 mL culture produced 22.4 mg of dry weight biomass containing 0.18 % (w/w) of carotenoids. On the other hand, carbon-deficient cultures (low C/N ratio) were observed to be optimum for C50 bacterioruberin production by Hfx. mediterranei, but negatively affected the growth of cells. Thus, a two-steps process was evaluated for optimum carotenoids yield. In the first step, a nutri-ent-repleted culture medium enabled the haloarchaea to produce biomass, while in the second step, the biomass was incubated under osmotic stress and in a carbon-deficient medium. Under the conditions used, the obtained biomass contained 0.27% (w/w) of carotenoids after seven days, which accounts for 58.49 µg·mL−1 of carotenoids for a culture with turbidity 14.0.This work was funded by a research grant from MINECO Spain (RTI2018-099860-B-I00) and the University of Alicante (VIGROB-309). We are also indebted to the Andalusian Government (research project BIO-214). ZM was assisted by a pre-doctoral grant from “Plan Propio de Investigación” of the University of Huelva, Spain. MG was awarded with a pre-doctoral fellowship from the Valencian Community Government (ACIF/2019/043)

Haloarchaeal Carotenoids: Healthy Novel Compounds from Extreme Environments

Haloarchaea are halophilic microorganisms belonging to the archaea domain that inhabit salty environments (mainly soils and water) all over the world. Most of the genera included in this group can produce carotenoids at significant concentrations (even wild-type strains). The major carotenoid produced by the cells is bacterioruberin (and its derivatives), which is only produced by this kind of microbes and few bacteria, like Micrococcus roseus. Nevertheless, the understanding of carotenoid metabolism in haloarchaea, its regulation, and the roles of carotenoid derivatives in this group of extreme microorganisms remains mostly unrevealed. Besides, potential biotechnological uses of haloarchaeal pigments are poorly explored. This work summarises what it has been described so far about carotenoids from haloarchaea and their production at mid- and large-scale, paying special attention to the most recent findings on the potential uses of haloarchaeal pigments in biomedicine.This work was partially funded by research grants from the MINECO Spain (CTM2013-43147-R; RTI2018-099860-B-I00) and University of Alicante (VIGROB-309)

Impact of microalgae-bacteria interactions on the production of algal biomass and associated compounds

A greater insight on the control of the interactions between microalgae and other microorganisms, particularly bacteria, should be useful for enhancing the efficiency of microalgal biomass production and associated valuable compounds. Little attention has been paid to the controlled utilization of microalgae-bacteria consortia. However, the studies of microalgal-bacterial interactions have revealed a significant impact of the mutualistic or parasitic relationships on algal growth. The algal growth, for instance, has been shown to be enhanced by growth promoting factors produced by bacteria, such as indole-3-acetic acid. Vitamin B12 produced by bacteria in algal cultures and bacterial siderophores are also known to be involved in promoting faster microalgal growth. More interestingly, enhancement in the intracellular levels of carbohydrates, lipids and pigments of microalgae coupled with algal growth stimulation has also been reported. In this sense, massive algal production might occur in the presence of bacteria, and microalgae-bacteria interactions can be beneficial to the massive production of microalgae and algal products. This manuscript reviews the recent knowledge on the impact of the microalgae-bacteria interactions on the production of microalgae and accumulation of valuable compounds, with an emphasis on algal species having application in aquaculture

Identification, biochemical composition and phycobiliproteins production of Chroococcidiopsis sp. from arid environment

Molecular and microscopic studies were performed to identify Chroococcidiopsis sp., an endolithic cyanobacterium, isolated from gypsum rocks of Atacama Desert (Chile). It was adapted to grow in mineral liquid medium, with 9 mM nitrate, bubbled with CO2-enriched air (2.5 % v/v), and continuously illuminated with a white light of 70 μmol photons m–2 s–1. The obtained biomass (productivity of 0.21 g L–1 d–1) had a C/N ratio of 6.67, and it contained carbohydrates (45.40 % of dry weight), proteins (36.72 %), lipids (5.60 %) nucleic acids (3.90 %) and ashes (8.28 %). The lipid fraction was particularly rich in palmitic (29.86 % of total fatty acids), linoleic (18.20 %), palmitoleic (12.75 %), linolenic (10.92 %), stearic (9.64 %) and capric acid (6.29 %). Chroococcidiopsis sp. accumulated phycobiliproteins in a light-dependent process and produced 204 mg g–1, under incident light of 10 μmol photons·m–2·s–1, with a relative abundance of 40.9 % for phycocyanin, 23.3 % for phycoerythrin, and 35.8 % for allophycocyanin. The biomass from this cyanobacterium can be a good source of these pigments, especially APC (maximum of 95 mg g dw−1), which are of interest for pharmacological, cosmetic, and food industries.Ministerio de Ciencia, Innovación y Universidades PGC2018–094076-B-I0