Natural habitats are often characterized by a low availability of
phosphate. In plants and many bacteria,
phosphate deficiency causes different physiological responses, including the replacement of phosphoglycerolipids in the membranes with nonphosphorous
lipids. We describe here a processive
glycosyltransferase (Pgt) in Mesorhizobium loti (Rhizobiales) involved in the synthesis of di- and triglycosyldiacylglycerols (DGlycD and TGlycD) during
phosphate deprivation. Cells of the corresponding Δpgt deletion mutant are deficient in DGlycD and TGlycD. Additional Pgt-independent
lipids accumulate in Mesorhizobium after
phosphate starvation, including diacylglyceryl trimethylhomoserine (DGTS) and
ornithine lipid (OL). The accumulation of the nonphosphorous
lipids during
phosphate deprivation leads to the reduction of phosphoglycerolipids from 90 to 50%. Nodulation experiments of Mesorhizobium wild type and the Δpgt mutant with its host plant, Lotus japonicus, revealed that DGlycD and TGlycD are not essential for nodulation under
phosphate-replete or -deficient conditions.
Lipid measurements showed that the Pgt-independent
lipids including OL and DGTS accumulate to higher proportions in the Δpgt mutant and therefore might functionally replace DGlycD and TGlycD during
phosphate deprivation.