Abstract
Washing A. xylinum whole cells in 0.01 m phosphate-0.003 m citrate, pH 6.2, leads to the release of particulate fractions which retain the ability to synthesize cellulose microfibrils from glucose and from UDPG. These fractions contain both outer and cytoplasmic membrane fragments. Frccze-etching shows the microfibrils to arise from outer membrane vesicles. A scheme to describe the synthesis of cellulose microfibrils by A. xylinum is proposed.