title: The effects of temperature and light intensity on growth, reproduction and EPS synthesis of a thermophilic strain related to the genus Graesiella.
abstract: Tunisian microalgae are diverse and rarely been studied. This study reports a first investigation of thermophile Chlorophyta isolated from mats community colonizing the geothermal springs in the north of Tunisia at water temperature 60 °C. In the study, the combined effect of temperature and light intensity was investigated on the cell growth, the mother and daughter cells abundance and the extracellular polymeric substances synthesis in batch culture of the isolated species. Three levels were tested for each factor, 20, 30, 40 °C for temperature; and 20, 70, 120 μmol photons m(-2) s(-1) for light intensity, using full factorial design and response surface methodology. The thermophile strain was identified as a genus Graesiella and showed 99.8% similarity with two Graesiella species: Graesiella emersonii and Graesiella vacuolata based on the 18S rDNA molecular identification. The optimal growth condition was found at 30 °C and 120 µmol photons m(-2) s(-1) (7 MC mL(-1) day(-1)), with the abundance of vegetative cells (daughter cells). In contrast, the number of mother cells increased significantly as the growth decreased; consequently, the highest ratio of auto spore mother cells versus daughter cells (19.4) was obtained at 20 °C and 20 µmol photons m(-2) s(-1). The highest yield of EPS production (11.7 mg L(-1) day(-1)) was recorded at the highest temperature (40 °C) and lowest light intensity (20 µmol photons m(-2)s(-1)). These results revealed how the species respond to high and low temperatures and suggest that the species should be considered as facultative thermophile.
authors.affiliation: Marine Biodiversity and Biotechnology Laboratory, National Institute of Marine Sciences and Technology, PO Box 59, 5000, Monastir, Tunisia, nahla.mezhoud@yahoo.fr.
authors.forename: Nahla
authors.initials: N
authors.lastname: Mezhoud
authors.forename: Fatma
authors.initials: F
authors.lastname: Zili
authors.forename: Nahla
authors.initials: N
authors.lastname: Bouzidi
authors.forename: Fatma
authors.initials: F
authors.lastname: Helaoui
authors.forename: Jihene
authors.initials: J
authors.lastname: Ammar
authors.forename: Hatem Ben
authors.initials: HB
authors.lastname: Ouada
mesh_terms: D001483:Base Sequence; D001704:Biopolymers / Q000096:biosynthesis*; D000460:Chlorophyta / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D048028:DNA, Algal / Q000235:genetics; D045482:Hot Springs / Q000382:microbiology; D007700:Kinetics; D008027:Light; D058086:Microalgae / Q000254:growth & development* / Q000302:isolation & purification / Q000378:metabolism*; D008954:Models, Biological; D013696:Temperature; D014416:Tunisia
chemical_list: D001704:Biopolymers; D048028:DNA, Algal