Alterations in Growth Temperature-range and Fatty-acid Composition of Thermus as a Result of Plasmid Elimination

Elimination of plasmids from Thermus flavus, T. thermophilus and three wild Thermus strains caused alterations in growth temperature range, pigmentation and membrane fatty acids without affecting viability. Following plasmid elimination all Thermus strains lost their ability to grow above 70-degrees-C. In addition, the minimum growth temperature was lowered by 5-10-degrees-C. Fatty acids were reduced by an average of approximately 35%. In addition, the contribution of iso- and ante-isobranched fatty acids were altered in four of the five strains. The iso C-15:0/iso C-17:0 ratio approached 1.0 in all strains, whereas the anteiso C-15:0/anteiso C-17:0 was reduced to 0.2. The iso C-16:0/normal-C-16:0 ratio increased in all strains due to an increase in iso C-16:0 in four strains and a reduction in normal-C-16:0 relative to iso C-16:0 in one strain. However, it was evident that the plasmid-free strains were able to compensate for these alterations in membrane fluidity to a certain extent by reducing the average chain length of isobranched acids. Altered fatty acid metabolism at the level of precursors may have influenced membrane composition and consequently growth temperature range.