Text Cylindrotheca closterium alga belongs to family Bacillariaceae, order
Bacillariales, class Bacillariophyceae and phylum Bacillariophyta. In this study
Cylindrotheca closterium alga was isolated from Alexandria coastal region
(Eastern Harbor) using two methods: dilution method and streak and spray
plating technique. Isolated algal cells were cultured on Guillard F2 liquid
medium. Morphological identification was carried out by light microscope and
scanning electric microscope. Algal cells were found to be wrapped by the
raphe canal of valves, which is a typical characteristic of Cylindrotheca
closterium shape. The cells contained two plastids lying next to each other
along the longitudinal axis of the cell and apprised to one side of the cell with
lobes extending onto the other sides, and the nucleus centrally in between.
However, previous studies indicated some morphological variations during the
life cycle of the alga.Genetic identification of Cylindrotheca closterium was
carried out using ribulose-bisphosphate carboxylase gene (rbcL) located in the
plastids as molecular marker. Specific PCR primers were used to amplify rbcL
gene fragment from total genomic DNA extracted from Cylindrotheca
closterium cells. Amplified rbcL (1177 bp) gene fragment was purified and
sequenced. Nucleotide sequence was compared with Cylindrotheca sequences
available in the GenBank. The Genetic distances and multi alignments were
computed by Pairwise Distance method using Clusteral W software analysis.
The nucleotide sequence of amplified rbcL gene showed varied identity
percentages (81, 80 and 78%) with other related sequences in the GenBank.
This could be correlated to the observed morphological variations. Previous
studies indicated high sequence divergences of rbcL gene among
Cylindrotheca isolates, and numerous nucleotide variations of rbcL gene
caused relatively few variation of deduced amino acid sequence. These results
may indicate that Cylindrotheca closterium is a species complex as was
previously evidenced by the variations of rbcL gene.