Observation of microtubule-like structures and crystalline array in Azotobacter vinelandii

Abstract

Many studies have been conducted on microtubules in eukaryotes, including protozoans, but few have dealt with similar structures in bacteria. Microtubule-1ike structures (MT) have been observed in Proteus mirabilis, Azotobacter vinelandii, and some bacterial L-forms . The function of these MT in prokaryotes is as yet undetermined. Microtubules in eukaryotes are involved in cytoskeleton support, cel1 motility, molecule transport, and the separation of chromosomes during mitosis . It has been suggested that A. vinelandii possesses forty chromosomes per cell , so this investigation speculates on the possibility these MT are involved in some form of chromosomal separation. While observing these structures a crystal lattice was noticed which has not been observed in the aforementioned prokaryotes.Cells were fixed for 10-20 min in 2% glutaraldehyde/0.1M sodium cacodylate (pH 7.2), washed with buffer, post-fixed with 1% OsO4, and stained with uranyl acetate. Samples were thin-sectioned, collected on carbon-coated parlodion- reinforced grids, and post-stained with lead citrate. Other preparations involved whole or lysed cells negatively stained with 2% phosphotungstic acid. All specimens exhibiting MT or the crystalline array were photographed in stereo pair.