Combined effect of the growth temperature and salinity of the medium on the accumulation of compatible solutes by Rhodothermus marinus and Rhodothermus obamensis

In this study we propose revised structures for the two major compatible so lutes of Rhodothermus marinus. We have also examined the accumulation of co mpatible solutes by the type strains of the slightly halophilic and thermop hilic species Rhodothermus marinus and Rhodothermus obamensis at several gr owth temperatures and salinities. The major solutes of R. marinus were iden tified as alpha-mannosylglycerate (alpha-MG) and alpha-mannosylglyceramide (alpha-MGA), whereas R. obamensis accumulated only alpha-mannosylglycerate. The total osmolyte content was higher during the early exponential phase a nd decreased abruptly as growth continued into the stationary phase. At low growth temperatures, R. marinus responded to water stress by accumulation of alpha-mannosylglycerate and its amide, in addition to low levels of treh alose, glutamate, and glucose. At the highest growth temperature, alpha-man nosylglycerate was the major compatible solute and alpha-mannosylglyceramid e was not detected. When both compounds were present, an increase in the sa linity of the growth medium favored the accumulation of alpha-mannosylglyce ramide over alpha-mannosylglycerate. The absence of alpha-mannosylglycerami de in R. obamensis at all growth temperatures and salinities constituted th e most pronounced difference in the profiles of compatible solute accumulat ion by the two strains. Trehalose was also a prominent solute in this organ ism. Both organisms accumulated higher levels of alpha-mannosylglycerate as the temperature was raised. The importance of the two compounds in the mec hanisms of thermoadaptation and osmoadaptation is discussed.