THE 18S rRNA GENE OF NAEGLERIA IN THE DNA DATABASES
The first sequence of the N. gruberi 18S rRNA gene sequence was reported by Clark and Cross, 1988. The sequence in N. gruberi was determined to be 2019 bp in length. Sequences of over 1800 bp from various isolates can be considered to constitute a database of “almost complete” 18S rRNA gene sequences. A number of isolates, especially in the taxa N. clarki, contain a large group I intron exceeding 1300 bp, resulting in a transcript for the 18S rRNA in excess of 3300 bp before the intron is spliced out.
Since the first N. gruberi sequence was obtained, 48 nearly complete sequences (> 1900 bp) from isolates within Naegleria have been deposited into the DNA databases. An additional 109 partial sequences have also been reported, including 17 sequences identified through environmental microbiome screens. The distribution of the lengths of the sequences reported in the databases is shown in the figure below. Two peaks are seen, 34 sequences between 600 and 700 bp in length, and 32 almost complete sequences between 2000 and 2100 bp in length.
Aligning the sequences from Naegleria exceeding 1900 bp in length can provide the basis for a phylogenetic analysis based on this gene. The tree obtained from these sequences is shown in the accompanying figure. The tree was constructed using the neighbor joining method in MEGA5. The root of the tree was determined using the sequence of Willaertia magna as an outgroup.
The references and accession numbers for the sequences deposited in the DNA databases are given in the accompanying REFERENCES page.