Searching for species in haloarchaea

Area of Science:

• Microbiology
• Systematic Biology
• Genomics

Background:

• Prokaryotic species definitions rely on clustering of individuals by genome content and gene similarity.
• Homologous recombination maintains similarity within clusters and allows divergence between them, forming the basis for applying the Biological Species Concept to prokaryotes.
• Recent efforts aim to use the Biological Species Concept for prokaryote systematics and ecology.

Purpose of the Study:

• To investigate species boundaries within the haloarchaeal genus Halorubrum.
• To assess the applicability of the Biological Species Concept to Halorubrum using multilocus sequence analysis.
• To evaluate the extent of gene exchange and barriers between Halorubrum populations from different saline environments.

Main Methods:

• Multilocus sequence analysis (MLSA) was employed.
• Isolates of the haloarchaeal genus Halorubrum were collected from diverse saline environments (Spanish saltern and Algerian saline lake).
• Concatenation of multiple marker sequences was used to define potential clusters.

Main Results:

• Clusters could be defined using concatenated marker sequences.
• Barriers to genetic exchange between these clusters were found to be leaky.
• Evidence suggests significant gene flow between populations.

Conclusions:

• No non-arbitrary method for circumscribing Halorubrum species is likely to emerge.
• The findings suggest that applying the Biological Species Concept broadly across prokaryotes may be problematic due to leaky gene flow barriers.
• Community agreement on arbitrary criteria may be necessary for practical prokaryotic species delineation.