Effects Of Temperature, Light And Nitrogen On The Growth And Trichome Morphology Of Cylindrospermopsis Raciborskii

Cylindrospermopsis raciborskii is a toxic bloom-forming cyanobacterium. It has beenspreading from tropical and subtropical to temperate water bodies because of globalenvironmental changes in recent years, which has a significant influence on the safety ofaquatic ecosystems and human health. In this study, eight strains of Cylindrospermopsisraciborskii were isolated and purified from Zhenhai Reservoir. The primer set27F/809Rspecifically targeting the cyanobacterial16S rDNA gene was used for PCR with the genomicDNA samples from eight strains. The16S rDNA sequences of our strains and19related genesequences downloaded from GeneBank were used to build a Neighhorjoining (NJ) tree. Inorder to investigate the response of Cylindrospermopsis raciborskii to ecological factors, three groups of experiments were set with6different temperatures,3different lightintensities, and3nitrogen forms with5different concentrations. The samples collected fromZhenhai reservoir were observed for the occurrence of Cylindrospermopsis raciborskii.Based on the laboratory experiments and field investigation, the adaptibility ofCylindrospermopsis raciborskii were showed as follows:(1) The16S rDNA sequences of C. raciborskii strains from different countries revealed a lowgenetic and geographical differentiation, and the genetic similarity exceeded99%.(2) Temperature excerted a significant effect on the growth and trichome morphology of C.raciborskii. Their specific growth rates were negative and the concentration of chlorophyll a(Chl a) was reduced sharply to10ug/L at12℃. The optimum growth temperature for bothstrains was28℃. The trichome length was relatively short in low and high temperaturetreatments, while the trichome width did not show any differences between differenttemperatures. Both strains did not produced heterocysts during the whole experimentalperiod.(3) C. raciborskii showed a wide adaptation to light intensity. When cultured under the lightintensities ranging from30μmol/m2/s~120μmol/m2/s, both strains exhibited no observabledifferences on Chl a concentrations, specific growth rates, trichome sizes and heterocystproportion in all treatments.(4) Nitrogen was an important factor affecting the growth and morphology of C. raciborskii. When cultured under nitrate concentrations ranging from2mg/L to247mg/L, both strainsshowed a similar growth trend and no obvious differentiation was observed in their trichomesizes. The growth of both strains was significantly inhibited by higher concentrations ofammonium and organic nitrogen. The optimum concentration of both nitrogen forms was8mg/L. The heterocyst appeared only under low nitrogen treatments (2mg/L~8mg/L) and itsheterocyst proportion increased and trichome length decreased under the lower nitrogenconcentration (2mg/L), the average trichome width showed no obvious differentiation in alltreatments.(5) The maximum abundance of C. raciborskii in Zhenhai reservoir was660cells/mL in August,2013when water temperature was30.5℃, with a total nitrogen concentration of0.75mg/L.Heterocyst proportion reached its peak (6.2%) at the same time. However, the averagetrichome sizes in field were smaller than those cultured in laboratory.