1,2-dipalmitoyl phosphatidylcholine, 1,2-dipalmitoyl phosphatidic acid or 1,2-dipalmitoyl- sn-glycerol inhibit sporangia formation and promote exponential growth of various frankia isolates from the casuarinaceae family

Abstract

Frankia strains from Casuarina (BR, S21, Thr), Allocasuarina (Allo2) and Gymnostoma (G80) genera were found to grow exponentially in stirred, propionate-containing BAP medium supplemented with 1.2 or 2.4 μ m synthetic 1,2-dipalmitoyl phosphatidylcholine, 1,2-dipalmitoyl phosphatidic acid or 1,2-dipalmitoyl- sn-glycerol. Phosphatidylcholines containing C15:0 or C17:0 acyl residues instead of C16:0 (palmitoyl) residues were equally beneficial but stearoyl (C18:0) residues favored the formation of small sporangia. Oleoyl residues (C18:1) appeared to be toxic as they produced a progressive post-exponential decrease in biomass. Our results suggest that phospholipids containing palmitoyl residues are part of the beneficial compounds present in the complex egg yolk phosphatidyl choline mixture which promote exponential growth of Frankia strains, inhibit sporangia formation and delay post-exponential biomass degradation. Phosphatidic acids do not appear to mediate the enhancing effect of phosphatidylcholine derivatives. The fact that 1,2-dipalmitoyl- sn-glycerol alone is beneficial, suggests that the phosphate and choline residues of the phosphatidylcholine molecule are not essential for balanced growth of Frankia under our conditions. Taken together our results suggest that a primary target of the beneficial compounds may be the plasma membrane of Frankia cells.