RNA-seq analysis was conducted to identify genes involved in adaptation to low-salinity conditions in two related Ulva species: U. prolifera restricted in brackish water (BW) and U. linza growing in seawater (SW). Samples of both organisms were cultured under either freshwater (FW), BW or SW, and their gene expression patterns were compared. The comparison between gene expression profiles of organisms cultured in FW and SW conditions identified 42 upregulated genes in U. prolifera and 139 in U. linza. Comparing organisms cultured in BW and SW conditions, 21 upregulated genes were identified in U. prolifera and 170 in U. linza. Moreover, the expression of 93 genes was downregulated in U. prolifera cultured in FW compared to SW and 51 genes in U. linza. In organisms cultured in BW compared to SW, 93 genes were downregulated in U. prolifera and 92 genes in U. linza. In both species, upregulated genes included genes functionally annotated as “ion transporters (DASS transporters),”and downregulated genes included genes annotated as“membrane”and“cell adhesion.”In U. prolifera, genes annotated “hydrolases (cell wall hydrolases)”were upregulated and those with“lipid metabolic process”were downregulated. Many genes annotated as“heat shock proteins”were upregulated in U. linza.
As potential competing species for the economically important resource kelp (Saccharina japonica var. ochotensis), the spatial distribution of two Sargassum species (Sargassum siliquastrum and S. boreale) on Rishiri and Rebun Island in northern Hokkaido, Japan, was observed by diving surveys (1993-2014). Oceanographic conditions of this coastal area were analyzed based on satellite images and particle-tracking experiments. We confirm the extension of the distribution of S. siliquastrum to the more northern areas on Rishiri (Kutsugata, from 2010) and Rebun islands (Funadomari, first found in 2014). The vertical distributions of S. siliquastrum and S. boreale were recorded along with environmental conditions in those habitats. One possible reason that an increase in sea surface temperature in August, the reproductive season of S. siliquastrum, and changes of the Tsushima Warm Current paths in the northern Sea of Japan might have affect their horizontal and vertical distribution.
The terrestrial cyanobacterium Nostoc commune accumulates high levels of radioactive material, but the mechanism had not been understood. Localization of Sr and Cs in N. commune was analyzed by using the analytical scanning electron microscopy. N. commune was cultured in a chemically defined liquid medium supplemented with CsCl or SrCl2・6H2O. N. commune absorbed high amount of Sr and Cs, but the cultured monilioid cells were contracted. As a result of energy dispersive X-ray spectrometer analysis, Sr and Cs were detected in both cell and jelly-like extracellular matrix. These results suggested that N. commune absorbed Sr and Cs in both cell and extracellular matrix.