Use of a fluorescence-based approach to assess short-term responses of the alga Pseudokirchneriella subcapitata to metal stress

This work explores the use of fluorescent probes to evaluate the responses of the green alga Pseudokirchneriella subcapitata to the action of three nominal concentrations of Cd(II), Cr(VI), Cu(II) and Zn(II) for a short time (6 h). The toxic effect of the metals on algal cells was monitored using the fluorochromes SYTOX Green (SG, membrane integrity), fluorescein diacetate (FDA, esterase activity) and rhodamine 123 (Rh123, mitochondrial membrane potential). The impact of metals on chlorophyll a (Chl a) autofluorescence was also evaluated. Esterase activity was the most sensitive parameter. At the concentrations studied, all metals induced the loss of esterase activity. SG could be used to effectively detect the loss of membrane integrity in algal cells exposed to 0.32 or 1.3 mol L1 Cu(II). Rh123 revealed a decrease in the mitochondrial membrane potential of algal cells exposed to 0.32 and 1.3 mol L1 Cu(II), indicating that mitochondrial activity was compromised. Chl a autofluorescence was also affected by the presence of Cr(VI) and Cu(II), suggesting perturbation of photosynthesis. In conclusion, the fluorescence-based approach was useful for detecting the disturbance of specific cellular characteristics. Fluorescent probes are a useful diagnostic tool for the assessment of the impact of toxicants on specific targets of P. subcapitata algal cells.The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013. Manuela D. Machado gratefully acknowledges the post-doctoral grant from FCT (SFRH/BPD/72816/2010)

Metabolic adaptation of a Chlamydomonas acidophila strain isolated from acid mine drainage ponds with low eukaryotic diversity

© 2018 Elsevier B.V. The diversity and biological characteristics of eukaryotic communities within acid mine drainage (AMD) sites is less well studied than for prokaryotic communities. Furthermore, for many eukaryotic extremophiles the potential mechanisms of adaptation are unclear. This study describes an evaluation of eight highly acidic (pH 1.6–3.1) and one moderately acidic (pH 5.6) metal-rich acid mine drainage ponds at a disused copper mine. The severity of AMD pollution on eukaryote biodiversity was examined, and while the most species-rich site was less acidic, biodiversity did not only correlate with pH but also with the concentration of dissolved and particulate metals. Acid-tolerant microalgae were present in all ponds, including the species Chlamydomonas acidophila, abundance of which was high in one very metal-rich and highly acidic (pH 1.6) pond, which had a particularly high PO4-P concentration. The C. acidophila strain named PM01 had a broad-range pH tolerance and tolerance to high concentrations of Cd, Cu and Zn, with bioaccumulation of these metals within the cell. Comparison of metal tolerance between the isolated strain and other C. acidophila strains previously isolated from different acidic environments found that the new strain exhibited much higher Cu tolerance, suggesting adaptation by C. acidophila PM01 to excess Cu. An analysis of the metabolic profile of the strains in response to increasing concentrations of Cu suggests that this tolerance by PM01 is in part due to metabolic adaptation and changes in protein content and secondary structure

Omics in algae: Paving the way for a systems biological understanding of algal stress phenomena?

The last decade, the biological and biomedical scientific landscape has seen the increase in use and applications of "omics" technologies. These technologies provide methods that allow for a comprehensive description of nearly all components within the cell. Microalgae not only play an important ecological role, but are also of commercial importance and therefore call for an in depth knowledge of basic biological functions. Knowledge of separate algal subsystems has gradually become available, but the challenge remains to integrate data obtained from these subsystems and from different levels of biological organization. Systems biology is a discipline that aims at this integration. In this paper, the current status of "omics" in algae is reviewed. At the lowest level, genome studies and the use of microarrays seem to have found widespread acceptance in algal research. At higher level such as the proteome and metabolome, however, very few omic studies have been carried out in algae so far. Moreover, the need arises for the construction of computer databases to store obtained information in a systematic way. To illustrate the use and especially the future needs of algal "omics" in a systems biological context, a case study is presented in which a freshwater alga was subjected to heavy metal stress and toxicity endpoints were monitored on different levels of biological organization

An omics based assessment of cadmium toxicity in the green alga Chlamydomonas reinhardtii

The effects of cadmium were assessed in the freshwater alga Chlamydomonas reinhardtii. Algae were exposed to concentrations of 0, 8.1 or 114.8 μM of cadmium and growth rates, gene transcription and metabolite profiles were examined after 48 and 72 h of exposure. In algae exposed to 8.1 μM Cd, several genes were differentially transcribed after 48 h but no adverse growth related effects were detected. A transient effect on both gene transcription patterns and metabolite profiles could be discerned after 48 h of exposure but the majority of these changes disappeared after 72 h. In contrast, all effects were more pronounced at the 114.8 μM cadmium exposure. Here growth was clearly reduced and transcription of a large number of genes involved in oxidative stress defense mechanisms was differentially increased. Metabolites involved in the glutathione synthesis pathway (an important antioxidant defense) were also affected but the effects of cadmium were found to be more pronounced at the transcript level than in the metabolome, suggesting that the former exhibits greater sensitivity toward cadmium exposure

Copper toxicity in the microalga Chlamydomonas reinhardtii: an integrated approach

The effects of copper exposure at five different concentrations on the freshwater alga Chlamydomonas reinhardtii were studied at the biochemical (metabolite), physiological (uptake kinetics and flow cytometry) and growth level. Changes at the physiological level were evident at the lowest exposure concentration while effects on the metabolome and on growth only occurred at the highest copper concentration tested. Flow cytometry revealed the presence of higher reactive oxygen species concentrations in algae exposed to higher copper concentrations and this was confirmed by a significant reduction in glutathione levels as part of the metabolomics assessment. Cu2? uptake kinetic data contributed information on possible mechanisms of copper toxicity, revealing that, a decrease in efflux pumping might be at the basis of an increased metal accumulation at higher exposure levels. This study demonstrates the value of using a comparative approach to investigating the mechanisms of toxicity rather than focusing on a single level of organization or effect