SPECIFIC LONG-CHAIN FATTY-ACIDS PROMOTE OPTIMAL-GROWTH OF FRANKIA - ACCUMULATION AND INTRACELLULAR-DISTRIBUTION OF PALMITIC AND PROPIONIC-ACID

Frankia isolates from nodules of the genera Casuarina (BR, S21, Thr), Allocasuarina (Allo2), and Gymnostoma (G80) were found to grow exponen tially with high biomass yield and minimal sporangia formation in stir red propionate mineral medium when supplemented either with 2.4 mu M p almitic acid (C16:0), pentadecanoic (C15:0), heptadecanoic (C17:0), or linoleic (C18:2, cis 9, 12) fatty acids. Strains also grew with lauri c (C12:0) or myristic (C14:0) acids, but gave lower biomass yield. Ste aric acid (C18:0) produced a good biomass yield, but cultures slowly a ccumulated sporangia; oleic acid (C18:1, cis-9) was detrimental to gro wth. Caprylic (C8:0) or capric (C10:0) acids proved to be prejudicial for long-term storage of Frankia strains. In experiments using labeled 1,2-dipalmitoyl phosphatidylcholine and palmitic acid, radioactivity bound rapidly to the insoluble, but solvent-extractable fraction of Fr ankia cells. In contrast, label from propionic acid accumulated in the cytosolic fraction. Therefore, the beneficial effect of some specific phosphatidylcholines or free fatty acids on Frankia growth appears to result from their utilization as building blocks for the membrane, su ggesting that membrane biosynthesis may be the limiting step for Frank ia growth in unamended propionate mineral medium.