Stress responses and metal tolerance of Chlamydomonas acidophila in metal-enriched lake water and artificial medium

Abstract

Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake-water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium-grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.

Photosynthesis in Extreme Environments

“…Similar results were found in C. reinhardtii in the presence of cadmium and copper (Boswell et al, 2002;Gillet et al, 2006), as well as in other photosynthetic organisms (Takamura et al, 1989;Wang et al, 2004). Although growth in extreme acidic environments is expected to require specific cellular adaptations of photosynthetic organisms, other studies have reported stress symptoms in acidophilic Chlamydomonas growing under acidic or metal-enriched natural water (Spijkerman et al, 2007;Langner et al, 2009). On the contrary, phytochrome B, phosphoribulokinase and phosphoglycerate kinase were up-regulated when cells were grown in metal rich acidic water .…”

“…In our case, this cannot be the reason, since phototrophic biofilms are the principal contributors of biomass www.intechopen.com in Río Tinto, representing over 65% of the total biomass (Lopez-Archilla et al, 2001). Another suggested reason for the low productivity in these extreme environments could be the lack of nutrients such as ammonium, phosphate or nitrate (Spijkerman et al, 2007). All the photosynthetic parameters analyzed showed statistical significant differences among species and sampling locations.…”

“…There are relatively few reports regarding photosynthesis in acidic environments in the literature, and most have focused on primary productivity measurements in acidic lakes. Thus, its been reported that minimum primary productivity is mainly due to metal stress (Niyogi et al, 2002;Hamsher et al, 2002) or soluble reactive phosphate concentration (Spijkerman et al, 2007). However, low pH itself does not reduce photosynthetic activity (Gyure et al, 1987).…”

“…Photoadaptation refers to changes in the genotype that arise either from mutations or from changes in the distribution of alleles within a gene pool, while photoacclimation refers to phenotypic adjustments that arise in response to variations of environmental factors. Besides nutrient limitation, presence of high concentrations of heavy metals could also explain the low values of maximum photosynthetic activity, since inhibition of www.intechopen.com photosynthesis is one of the most important cellular responses to metal stress conditions (Hanikenne, 2003;Spijkerman et al, 2007). Thus, a significant decrease in the amount of some photosynthetic proteins (RuBisCo, cytrochrome C peroxidase or photosystem I 11K protein precursor ) has been reported in an isolate of Chlamydomonas spp.…”

Significant habitat effects influence protist fitness: evidence for local adaptation from acidic mining lakes

“…This stenoecious, specialist species (Gerloff-Elias et al 2005, Spijkerman et al 2007 has been recorded from AML and extremely acid rivers (pH ;2) in Europe and from different environments on other continents (Amaral Zettler et al 2002, Gerloff-Elias et al 2005; (2) two closely related, but different flagellate species, Ochromonas spp., the dominant bacterivore in these mining lakes accounting for the consumption of up to 90% of the daily bacterial production (Schmidtke et al 2006), and (3) two ciliate species of the genus Oxytricha that were isolated from two similar, but geographically distant AML in Austria and Germany. Oxytricha is the only ciliate genus encountered in all our study lakes (T. Weisse et al, unpublished manuscript).…”