title: The molecular dimension of microbial species: 2. Synechococcus strains representative of putative ecotypes inhabiting different depths in the Mushroom Spring microbial mat exhibit different adaptive and acclimative responses to light.
abstract: Closely related strains of thermophilic Synechococcus were cultivated from the microbial mats found in the eﬄuent channels of Mushroom Spring, Yellowstone National Park (YNP). These strains have identical or nearly identical 16S rRNA sequences but are representative of separate, predicted putative ecotype (PE) populations, which were identified by using the more highly resolving psaA locus and which predominate at different vertical positions within the 1-mm-thick upper-green layer of the mat. Pyrosequencing confirmed that each strain contained a single, predominant psaA genotype. Strains differed in growth rate as a function of irradiance. A strain with a psaA genotype corresponding to a predicted PE that predominates near the mat surface grew fastest at high irradiances, whereas strains with psaA genotypes representative of predominant subsurface populations grew faster at low irradiance and exhibited greater sensitivity to abrupt shifts to high light. The high-light-adapted and low-light-adapted strains also exhibited differences in pigment content and the composition of the photosynthetic apparatus (photosystem ratio) when grown under different light intensities. Cells representative of the different strains had similar morphologies under low-light conditions, but under high-light conditions, cells of low-light-adapted strains became elongated and formed short chains of cells. Collectively, the results presented here are consistent with the hypothesis that closely related, but distinct, ecological species of Synechococcus occupy different light niches in the Mushroom Spring microbial mat and acclimate differently to changing light environments.
authors.affiliation: Department of Mathematical Sciences, Montana State University, Bozeman MT, USA ; School of Environmental Sciences, University of Guelph, Guelph ON, Canada.
authors.forename: Shane
authors.initials: S
authors.lastname: Nowack
authors.affiliation: Department of Land Resources and Environmental Sciences, Montana State University, Bozeman MT, USA.
authors.forename: Millie T
authors.initials: MT
authors.lastname: Olsen
authors.affiliation: Department of Land Resources and Environmental Sciences, Montana State University, Bozeman MT, USA.
authors.forename: George A
authors.initials: GA
authors.lastname: Schaible
authors.affiliation: Department of Land Resources and Environmental Sciences, Montana State University, Bozeman MT, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Becraft
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park PA, USA.
authors.forename: Gaozhong
authors.initials: G
authors.lastname: Shen
authors.affiliation: Department of Mathematical Sciences, Montana State University, Bozeman MT, USA ; Department of Mathematics, Temple University, Philadelphia, PA USA.
authors.forename: Isaac
authors.initials: I
authors.lastname: Klapper
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park PA, USA ; Department of Chemistry and Biochemistry, Montana State University, Bozeman MT, USA.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
authors.affiliation: Department of Land Resources and Environmental Sciences, Montana State University, Bozeman MT, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Ward
keywords: cyanobacteria; light acclimation; light adaptation; microbial species; photosynthesis