STUDIES ON FIBRILS PRODUCED BY MYXOCOCCUS XANTHUS

Abstract

4 - 5 rm diameter fibrils were originally observed in 2% phosphotungstate- negatively stained, 10* x g supernatant fractions of French Pressure Cell-disruptedM. xanthus FB vegetative cells. The fibrils are also present in the periplasmic fraction prepared by osmotic shock; treatment of cells with pronase (100 jig/ml; 30 min.) prior to osmotic shock increases the number of fibrils observed. They are also present in 10° Xie pellets of culture medium in which logarithmic phase cells had been growing. Aggregates of fibrils are observed in association with gliding cells on filmed electron microscope grids which have been pressed on the edges of colonies. Cells of at least one non-motile mutant also produce these structures. One hypothesis concerning the nature of the fibrils is that they are comparable to eukaryotic actin. This was based on their structure and on the presence of a major protein constituent (molecular weight of approximately 50,000) recovered in a procedure designed to extract actin from ™. xanthus. However, attempts to decorate the fibrils with rabbit heavy meromyosin have been unsuccessful. Not all fibrils are sedimented by centrifugation at 150,000 x g for 90 min. Fibrils are restitant to digestion by pronase and by lysozyme; treatment with sodium dedecyl] sulfate (1 %; 70 3 does not alter their morphology. We hypothesize that fibrils, produced by vegetative cells, serve as tracks on which cells glide. These tracks may account for the phase-bright trails left by gliders on agar.