Comparison of Growth Performance, Pigment Synthesis, and Esterase Activity of Synechococcus sp. HS01 and Limnothrix sp. KO01 in Response to Cadmium Toxicity.

Various studies have been conducted to understand the impact of environmental pollutants on cyanobacteria due to their abundant presence in aquatic and terrestrial environments, specific morphological and physiological characteristics, and high ecological flexibility in response to environmental changes. Here, the effect of different concentrations of cadmium on two native strains of cyanobacteria, namely Synechococcus sp. HS01 and Limnothrix sp. KO01 was studied and compared with each other. In this regard, the cyanobacterial growth, pigment contents, and esterase enzyme activity were evaluated after exposure of the cells to different concentrations of cadmium (II). The toxic effects of Cd(II) on the growth rate of Limnothrix sp. KO01, even at low concentrations, tended to be higher than those for Synechococcus sp. HS01. The content of pigments decreased by an increase in Cd(II) concentration. In compliance with the cell growth, the changes occurred in pigment contents of Limnothrix sp. KO01 was more sensitive than Synechococcus sp. HS01 in the presence of different concentrations of cadmium. Flow cytometry analysis of Cd(II) effects on esterase activity of both strains after 6, 24, 48, and 72 h of exposure to Cd(II) concentrations of 9, 27, 63, and 90 µM showed that tolerance to Cd(II) toxicity in Limnothrix sp. KO01 is less than Synechococcus sp. HS01. The results obtained in this study suggest high potentials of Synechococcus sp. HS01 for heavy metal bioaccumulation due to its considerable tolerance to cadmium.

Cadmium uptake capacity of an indigenous cyanobacterial strain, Nostoc entophytum ISC32: new insight into metal uptake in microgravity-simulating conditions.

Among nine cyanobacterial strains isolated from oil-contaminated regions in southern Iran, an isolate with maximum cadmium uptake capacity was selected and identified on the basis of analysis of morphological criteria and 16S rRNA gene sequence similarity as Nostoc entophytum (with 99% similarity). The isolate was tentatively designated N. entophytum ISC32. The phylogenetic affiliation of the isolates was determined on the basis of their 16S rRNA gene sequence. The maximum amount of Cd(II) adsorbed by strain ISC32 was 302.91 mg g(-1) from an initial exposure to a solution with a Cd(II) concentration of 150 mg l(-1). The cadmium uptake by metabolically active cells of cyanobacterial strain N. entophytum ISC32, retained in a clinostat for 6 days to simulate microgravity conditions, was examined and compared with that of ground control samples. N. entophytum ISC32 under the influence of microgravity was able to take up cadmium at amounts up to 29% higher than those of controls. The activity of antioxidant enzymes including catalase and peroxidase was increased in strain ISC32 exposed to microgravity conditions in a clinostat for 6 days, as catalase activity of the cells was more than three times higher than that of controls. The activity of the peroxidase enzyme increased by 36% compared with that of the controls. Membrane lipid peroxidation was also increased in the cells retained under microgravity conditions, up to 2.89-fold higher than in non-treated cells. Images obtained using scanning electron microscopy showed that cyanobacterial cells form continuous filaments which are drawn at certain levels, while the cells placed in a clinostat appeared as round-shaped, accumulated together and distorted to some extent.

Lipid production and mixotrophic growth features of cyanobacterial strains isolated from various aquatic sites.

The present study was conducted to determine the potential of five cyanobacteria strains isolated from aquatic zones to induce lipid production. The phylogenetic affiliation of the isolates was determined by 16S rRNA gene sequencing. Amongst the isolates, an efficient cyanobacterium, Synechococcus sp. HS01 showing maximal biomass and lipid productivity, was selected for further studies. In order to compare lipid productivity, the HS01 strain was grown in different media to screen potential significant culture ingredients and to evaluate mixotrophic cultivation. Mixotrophic cultivation of the strain using ostrich oil as a carbon source resulted in the best lipid productivity. GC analysis of fatty acid methyl esters of the selected cyanobacterial strain grown in media supplemented with ostrich oil showed a high content of C16 (palmitoleic acid and palmitic acid) and C18 (linoleic acid, oleic acid and linolenic acid) fatty acids of 42.7 and 42.8 %, respectively. Transmission electron micrographs showed that the HS01 cells exhibited an elongated rod-shaped appearance, either isolated, paired, linearly connected or in small clusters. According to initial experiments, ostrich oil, NaNO3 and NaCl were recognized as potential essential nutrients and selected for optimization of media with the goal of maximizing lipid productivity. A culture optimization technique using the response surface method demonstrated a maximum lipid productivity of 56.5 mg l(-1) day(-1). This value was 2.82-fold higher than that for the control, and was achieved in medium containing 1.12 g l(-1) NaNO3, 1 % (v/v) ostrich oil and 0.09 % (w/v) NaCl.