Genome diversity in the cyanobacterium Nostoc linckia at 'Evolution canyon', Israel, revealed by inter-HIP1 size polymorphisms

The relationship between genomic diversity and environmental heterogeneity and stress was assessed in the cyanobacterium Nostoc linckia, across the sharp microclimatic contrasts of opposing slopes in 'Evolution Canyon', Mt. Carmel, Israel. 'Evolution Canyon' is a microcosm model of life with south-and north-facing slopes (SFS and NFS) that share a limestone lithology but contrast biotically, primarily due to interslope differences in solar radiation, resulting in higher rock temperatures on the south-facing slopes. The cyanobacterium N. linckia, a sessile prokaryote that grows in the canyon on limestone rock surfaces, is exposed to fluctuations of solar radiation, temperature and desiccation. We found remarkable differences in genomic diversity of N. linckia subpopulations between slopes (interslope) and within elevations of the south-facing slopes (intraslope). These differences were assessed by amplification of genomic DNA with primers based on the highly iterated palindrome (HIP1) (5′-GCGATCGC-3′), thereby revealing the diversity among the HIPl sites (inter-HIP1 polymorphism) in the genome of N. linckia. The interslope divergence was demonstrated by significantly higher diversity (He and v) and polymorphism (p) indices on the heterogeneous south-facing slopes, due in particular to the upper and middle elevations (SFS 1 and SFS 2). The intraslope divergence on the south-facing slopes reflects an upslope increase in genetic diversity indices with xeric microclimate, across the slope. Correlations were found between p and He and variables influencing aridity stress: solar radiation, temperature and day-night temperature differences. This may imply that the major cause for the inter-and intraslope genetic divergence is the differences in their microclimatic conditions. We show that the genetic diversity of N. linckia in 'Evolution Canyon' revealed by I-HIP1 is related to heterogeneity and stress at a microsite, and appears to be moulded by natural selection as a genomic adaptive strategy to cope with climatic stress. This could highlight the importance of ecological stress and selection in evolution and its remarkable effect on the genetic system across the prokaryotic genome. Our results indicate that I-HIP1 can be exploited not only as a genetic marker, but also as a genetic monitor for the response to climatic stress. This conclusion supports the suggestion that HIP1 is involved in promoting genome diversity in cyanobacteria.