Isolation and genetic identification of Cylindrotheca closterium algae from Alexandria coastal region

Text Cylindrotheca closterium alga belongs to family Bacillariaceae, orderBacillariales, class Bacillariophyceae and phylum Bacillariophyta. In this studyCylindrotheca closterium alga was isolated from Alexandria coastal region(Eastern Harbor) using two methods: dilution method and streak and sprayplating technique. Isolated algal cells were cultured on Guillard F2 liquidmedium. Morphological identification was carried out by light microscope andscanning electric microscope. Algal cells were found to be wrapped by theraphe canal of valves, which is a typical characteristic of Cylindrothecaclosterium shape. The cells contained two plastids lying next to each otheralong the longitudinal axis of the cell and apprised to one side of the cell withlobes extending onto the other sides, and the nucleus centrally in between.However, previous studies indicated some morphological variations during thelife cycle of the alga.Genetic identification of Cylindrotheca closterium wascarried out using ribulose-bisphosphate carboxylase gene (rbcL) located in theplastids as molecular marker. Specific PCR primers were used to amplify rbcLgene fragment from total genomic DNA extracted from Cylindrothecaclosterium cells. Amplified rbcL (1177 bp) gene fragment was purified andsequenced. Nucleotide sequence was compared with Cylindrotheca sequencesavailable in the GenBank. The Genetic distances and multi alignments werecomputed by Pairwise Distance method using Clusteral W software analysis.The nucleotide sequence of amplified rbcL gene showed varied identitypercentages (81, 80 and 78%) with other related sequences in the GenBank.This could be correlated to the observed morphological variations. Previousstudies indicated high sequence divergences of rbcL gene amongCylindrotheca isolates, and numerous nucleotide variations of rbcL genecaused relatively few variation of deduced amino acid sequence. These resultsmay indicate that Cylindrotheca closterium is a species complex as waspreviously evidenced by the variations of rbcL gene.