Environmental factors driving the occurrence of the invasive cyanobacterium Sphaerospermopsis aphanizomenoides (Nostocales) in temperate lakes.

Cyanobacterial blooms are an increasing threat worldwide. Invasions of certain cyanobacterial species, mainly towards higher latitudes, add to this concern as they enrich the pool of potential bloom-formers in the invaded region. Among the numerous causes of this escalating process, climate warming is commonly considered the most crucial factor, but empirical studies of this issue are lacking. The aim of our study was to identify physical, chemical and biological factors related to the occurrence of an invasive cyanobacterium at the northern border of its putative current range, and thus enabling its expansion. This study focuses on the relatively little studied species Sphaerospermopsis aphanizomenoides (Nostocales, Cyanobacteria; synonyms: Aphanizomenon aphanizomenoides, Anabaena aphanizomenoides), which is predicted to become one of the main nuisance species of the future. Forty-nine freshwater lakes located between latitudes 51° and 55°N were examined for the presence of S. aphanizomenoides, and environmental factors that could drive its occurrence were studied simultaneously. To identify factors correlated with the presence of the species, principal component analysis (PCA) and Mann-Whitney U test were performed. Water temperature did not differentiate lakes with or without S. aphanizomenoides, however the study was conducted in a particularly hot summer. Total phosphorus concentration was identified as the primary driving factor of the occurrence of S. aphanizomenoides. The species grew in poor light conditions and high phytoplankton biomass, mainly in shallow lakes. As shown by detrended correspondence analysis (DCA), the species accompanied shade tolerant, eutrophic species of native and invasive cyanobacteria as well as eukaryotic algae. Our results indicate that eutrophication may be the primary factor enabling the increasing occurrence of S. aphanizomenoides in temperate environments, and suggest that this process may stimulate expansion of cyanobacterial species towards high latitudes.

First and second line mechanisms of cadmium detoxification in the lichen photobiont Trebouxia impressa (Chlorophyta).

"First line" defence mechanisms, such as phytochelatin biosynthesis, and "second line" mechanisms, such as stress protein induction, were investigated in cadmium-exposed cells of Trebouxia impressa Ahmadjian, a green microalgal species that is a common photobiont of the lichen Physcia adscendens (Fr.) H. Olivier. When T. impressa cells were exposed to 0, 9 and 18 microM Cd for 6, 18 and 48 h, glutathione and phytochelatins efficiently protected the cells against Cd damage. By contrast, the highest Cd concentration (36 microM) at the longest exposure-time (48 h) caused marked drops in glutathione and phytochelatin content, several types of ultrastructural damage, and decreases in cell density and total chlorophyll concentration. In this case, induction of stress proteins was observed, but only long after the induction of phytochelatins. Thus, stress proteins could represent a "second line" mechanism to counteract Cd stress, activated when there is a decline in the "first line" mechanism of Cd detoxification given by phytochelatins.

Arsenic availability, toxicity and direct role of GSH and phytochelatins in As detoxification in the green alga Stichococcus bacillaris.

Accumulation and toxicity of inorganic arsenic forms As(III) and As(V) to the green microalga Stichococcus bacillaris depended on environmental variables. pH of exposure and to a lesser extent elevated concentrations of humic acid, chloride and orthophosphate ions affected arsenic accumulation and its toxicity. As(V) was more toxic than As(III), especially at the near neutral pH 6.8. Intracellular As(V) uptake by algal cells was greater at pH 6.8 than at 8.2. In response to As(III) and As(V) the alga produced phytochelatins (PC(2-3)), but at As(V) exposure, their levels in cells were higher than with As(III), suggesting higher As(V) than As(III) availability and uptake. Arsenic in algal cells occurred in various complexes with non-protein SH groups. Some of these complexes dissociated under acidic conditions, but others were able to dissociate only at an alkaline pH. The former consisted of SH groups of phytochelatins. Those dissociating at an alkaline pH involved SH groups from both glutathione (GSH) and phytochelatins (PC) or their derivatives. In the predominant acid-stable mixed As-SH complex, the ratio of SH (PC(2)) to SH (GSH) was 2:1, which suggests that one molecule of PC(2) (containing two SH groups) together with one molecule of GSH were involved in intracellular complexation of each As atom. This is the first demonstration of GSH involvement in arsenic complexation, in vivo. The intracellular concentration of As was greater than that of non-protein SH groups which suggests that not all the arsenic in algal cells was complexed and detoxified by thiol groups.

Phytochelatin production in freshwater algae Stigeoclonium in response to heavy metals contained in mining water; effects of some environmental factors.

Production of phytochelatins (PC) in two freshwater, filamentous green algae of the genus Stigeoclonium, in response to heavy metals contained in mining water was studied. Stigeoclonium sp. grown abundantly in ditches with the mining water (southern Poland) accumulated high amounts of heavy metals. The other studied alga Stigeoclonium tenue Kütz. was isolated from unpolluted lake water in the Netherlands. Both algae exposed to the heavy metal mixture (17 microM; mainly zinc) contained in the hard, alkaline (pH 8.2) mining water produced similar amounts of phytochelatins (PC2 and PC3): 500-600 nmol SH g(-1) dry weight. After water acidification to pH 6.8, a > 2-fold increase of the total phytochelatin level as well as the appearance of longer chain peptide PC4 in the cells of both algae was observed. The concentration of labile forms of zinc in the acidified mining water was four times as high as that in the alkaline water. The heavy metal mixture (17 microM) in non-complexing solution of pH 6.8 caused a comparable phytochelatin production in both Stigeoclonium strains as the same mixture present in the acidified mining water. However, in the non-complexing solution of pH 8.2, the metal mixture induced in algae more PCs than at pH 6.8. A positive effect of bicarbonate enrichment in the solution on the PC production in S. tenue was also observed. Stigeoclonium sp. exposed to high concentrations (10 microM) of individual metals (Zn, Pb and Cd available as free cations) synthesised much higher amounts of phytochelatins (PC2-PC4) than in response to the metal mixture contained in the mining water. The order of PC induction by the studied metals in the Stigeoclonium sp. was Cd > Pb > Zn. Addition of suspended solid matter to the heavy metal solution resulted in essential quantitative changes in phytochelatins in algal cells; a considerable decrease of PC2, PC3 and PC4 levels was observed. The PC production in algae of the genus Stigeoclonium exposed to the heavy metal mixture is discussed in the context of various metal bioavailability and the algal adaptation to complex aquatic environment.

The impact of inorganic tin on the planktonic cyanobacterium Synechocystis aquatilis: the effect of pH and humic acid.

The influence of inorganic tin compounds on the unicellular cyanobacterium Synechocystis aquatilis was studied, and its dependence on changing pH of the surrounding medium and the presence of humic acid. Both Sn(II) and Sn(IV), used as chlorides (at the concentrations 1-10 mg litre(-1)), inhibit the growth and chlorophyll a content of the cyanobacterium cultures, but only under alkaline conditions. Generally, the observed tin toxicity increased with increase of metal concentration, time of exposure and pH value of the medium (in the range 7-9.8). Sn(II) seems to be more toxic than Sn(IV). At the lowest studied metal concentration (1 mg litre(-1)), Sn(II) caused a 36 and 40% decrease in growth and chl a content, respectively, after 96 h exposure at pH 9.8, while Sn(IV) caused even a slight increase of both physiological parameters (hormetic effect). Similar increases in growth and chl a content were also observed at a high Sn (II) and Sn(IV) concentration (10 mg litre(-1)), but only in cultures exposed to metal at pH 7. At high pH (9.8), 10 mg litre(-1) of Sn(II) and Sn(IV) significantly suppressed both the growth of the cyanobacterium (by 54.2 and 26.1%, respectively) and the chl a content in cultures (by 58.2 and 24%, respectively). Humic acid reduced the toxicity of tin towards the cyanobacterium. The observed effects of pH and complexing ligand on the inorganic tin toxicity are discussed in the context of changing, chemical metal speciation and bioavailability.