Species, Sequence Types and Alleles: Dissecting Genetic Variation in Acanthamoeba

Area of Science:

• Microbiology
• Molecular Biology
• Evolutionary Biology

Background:

• Species identification in Acanthamoeba is complicated by pleomorphic morphology, hindering accurate classification.
• Molecular methods like DNA sequencing have been used, but a complete resolution of Acanthamoeba taxonomy remains elusive.
• The concept of sequence types, based on nuclear 18S rRNA gene sequences, was introduced to quantitatively assess differences among Acanthamoeba isolates.

Purpose of the Study:

• To address the confusion arising from redundant labeling of genetic variations (alleles) within Acanthamoeba sequence types.
• To tabulate and determine the frequencies of alleles within the ASA.S1 hypervariable region of the 18S rRNA gene in international DNA databases.
• To gain new insights into the evolutionary history and genetic diversity of Acanthamoeba, potentially clarifying species definitions.

Main Methods:

• Analysis of nuclear 18S rRNA gene sequences from Acanthamoeba isolates available in international DNA databases.
• Focus on the hypervariable region designated ASA.S1 to scrutinize genetic variation.
• Tabulation and frequency determination of identified alleles across different sequence types (T3, T4, T5, T11, T15, and supergroup T2/6).

Main Results:

• Over 150 distinct alleles were identified more than once within more than 3500 isolates of sequence type T4.
• Previous studies identified ten alleles in type T4 and five in type T3 isolates from Hong Kong.
• Data from smaller samples of other sequence types (T3, T5, T11, T15, and T2/6) were also obtained and analyzed.

Conclusions:

• The extensive allelic variation within Acanthamoeba sequence types highlights the complexity of its genetic diversity.
• This comprehensive analysis of alleles provides a more unified approach to understanding Acanthamoeba genetic variation.
• The findings offer crucial insights into the evolutionary trajectory of Acanthamoeba and contribute to defining species boundaries within the genus.