Cyanobacteria form extensive macroscopic mats in shallow freshwater environments in the High Arctic and Antarctic. In these habitats, the communities are exposed to seasonal freezing and desiccation as well as to freeze-thawing and drying-rewetting cycles. Here, we characterized the annual cycles of two Phormidium communities in very shallow seepages located in central Svalbard. We observed the structure of the communities and the morphology, ultrastructure, metabolic activity, and viability of filaments and single cells. The communities overwintered as frozen mats, which were formed by long filaments enclosed in thick multilayered polysaccharide sheaths. No morphologically and/or ultrastructurally distinct spore-like cells were produced for surviving the winter, and the winter survival of the communities was not provided by a few resistant cells, which did not undergo visible morphological and ultrastructural transformations. Instead, a high proportion of cells in samples (85%) remained viable after prolonged freezing. The sheaths were the only morphological adaption, which seemed to protect the trichomes from damage due to freezing and freeze-associated dehydration. The cells in the overwintering communities were not dormant, as all viable cells rapidly resumed respiration after thawing, and their nucleoids were not condensed. During the whole vegetative season, defined by the presence of water in a liquid state, the communities were constantly metabolically active and contained <1% of dead and injured cells. The morphology and ultrastructure of the cells remained unaltered during observations throughout the year, except for light-induced changes in thylakoids. The dissemination events are likely to occur in spring as most of the trichomes were split into short fragments (hormogonia), a substantial proportion of which were released into the environment by gliding out of their sheaths, as well as by cracking and dissolving their sheaths. The short fragments subsequently grew longer and gradually produced new polysaccharide sheaths.

Botany Department Faculty of Science University of South Bohemia České Budějovice Czech Republic

Centre for Polar Ecology Faculty of Science University of South Bohemia České Budějovice Czech Republic

Institute of Botany Academy of Sciences of the Czech Republic Třeboň Czech Republic

Zobrazit více v PubMed

Proc Natl Acad Sci U S A. 2008 Dec 2;105(48):18854-9 PubMed

Appl Environ Microbiol. 1991 Mar;57(3):645-8 PubMed

Am J Physiol. 1984 Sep;247(3 Pt 1):C125-42 PubMed

Nat Rev Microbiol. 2010 Jan;8(1):39-50 PubMed

Microbiol Mol Biol Rev. 2002 Mar;66(1):94-121; table of contents PubMed

PLoS One. 2013;8(2):e55283 PubMed

Philos Trans R Soc Lond B Biol Sci. 2002 Jul 29;357(1423):937-43 PubMed

Front Microbiol. 2015 Apr 08;6:278 PubMed

J Bacteriol. 2000 Mar;182(5):1191-9 PubMed

J Bacteriol. 1991 Jul;173(13):4188-94 PubMed

J Bacteriol. 1992 Jan;174(2):345-8 PubMed

Environ Microbiol. 2005 Apr;7(4):519-29 PubMed

Plant Physiol. 1998 Sep;118(1):1-8 PubMed

Mol Microbiol. 2004 Jan;51(2):395-405 PubMed

Microbiol Rev. 1994 Jun;58(2):211-32 PubMed

FEMS Microbiol Rev. 2010 Jul;34(4):476-95 PubMed

J Phycol. 2013 Dec;49(6):1167-80 PubMed

FEMS Microbiol Rev. 2009 Sep;33(5):917-41 PubMed

Biol Rev Camb Philos Soc. 2009 Aug;84(3):449-84 PubMed

Experimental freezing of freshwater pennate diatoms from polar habitats