Small subunit ribosomal RNA evolution in the genus Acanthamoeba

Reverse transcription of small subunit ribosomal RNA (srRNA) was used to determine the partial nucleotide sequences of the srRNA of seven isolates of Acanthamoeba. These seven sequences and the sequence of the corresponding region in an A. castellanii previously totally sequenced were compared in order to investigate evolution of the srRNA gene in Acanthamoeba. The results of the comparisons were consistent with the hypotheses that the genus is monophyletic, that the Pussard and Pons grouping system is valid, that the Acanthamoeba expansion segments in the srRNA gene evolve at a much faster rate than the rest of the gene, and that the extent of nucleotide sequence divergence in the genus Acanthamoeba is roughly similar to that differentiating vertebrates and invertebrates.

Pathogenicity of Acanthamoeba and a Corynebacterium in the rat cornea

Acanthamoeba keratitis is a sight-threatening disease that is difficult to treat. The development of an animal model is necessary for many of the studies required to improve visual outcome in human patients. A rat model is proposed that is dependent on coinoculation of amebae and corynebacteria into the corneal stroma. The infective dose was determined for a virulent Acanthamoeba isolate and was used to screen 17 other isolates, including 7 from the human cornea. A total of 6 were infective in the rat cornea. The model should be useful for controlled in vivo studies of this intractable condition.

srRNA evolution and phylogenetic relationships of the genus Naegleria (Protista: Rhizopoda)

A rapid RNA sequencing technique was used to partially sequence the small-subunit ribosomal RNA (srRNA) of four species of the amoeboid genus Naegleria. The extent of nucleotide sequence divergence between the two most divergent species was roughly similar to that found between mammals and frogs. However, the pattern of variation among the Naegleria species was quite different from that found for those species of tetrapods characterized to date. A phylogenetic analysis of the consensus Naegleria sequence showed that Naegleria was not monophyletic with either Acanthamoeba castellanii or Dictyostelium discoideum, two other amoebas for which sequences were available. It was shown that the semiconserved regions of the srRNA molecule evolve in a clocklike fashion and that the clock is time dependent rather than generation dependent.

A temporary flagellate (mastigote) stage in the vahlkampfiid amoeba Willaertia magna and its possible evolutionary significance

A temporary flagellate (mastigote) stage has been observed in several isolates of the vahlkampfiid amoeba Willaertia magna. In an Australian isolate studied in detail, flagellates appeared synchronously, although later than in Naegleria fowleri or N. lovaniensis under similar conditions (half-maximal time, t50 = 168 min at 37 degrees C). The flagellates initially have four flagella and lack a cytostome, but undergo several successive divisions, the first of them synchronous, resulting in progressive reduction in cell volume. New flagella appear during and after division, and the number of flagella in daughter cells of later divisions is rather variable. Comparison of these observations with descriptions of other amoeboflagellates confirms that Willaertia is a valid genus. A likely sequence of morphological changes in the evolution of Willaertia and Naegleria from a hypothetical ancestral vahlkampfiid is proposed.

Determinants of the microbiological characteristics of South Australian swimming pools

A survey of 100 swimming pools has been conducted to assess the effectiveness of disinfection practices against various microorganisms and to check compliance with recommended chlorine levels and pH. Microbiological quality was assessed from densities of total coliforms, Escherichia coli, and Pseudomonas aeruginosa, total colony counts, and the presence or absence of amoebae, including the pathogen Naegleria fowleri. Although a free chlorine residual of 1.0 mg/liter and a pH range of 7.0 to 7.6 are recommended by local health authorities, 41 pools had a lower free chlorine residual and 37 had a pH outside this range. Multiple logistic regression analysis was used to test the association of field measurements with the microbiological data. The analysis demonstrated a strong positive association of free chlorine with bacteriological quality and the absence of Naegleria spp. No other field measurement was predictive in this regard, although the absence of all amoebae was associated with a relatively low water temperature and pH. Using a mathematical model derived from this analysis, it was estimated that 99% of pools would have acceptable bacteriological quality and 94% would be free of Naegleria spp. at a free chlorine residual of 1.0 mg/liter. However, at the mean water temperature (23 degrees C) and pH (7.5) seen in this study, other amoebae would still be detectable in 500-ml samples taken from 40% of pools at this chlorine level.