Effect of external environmental factors on the morphology of Spiroplasma citri

An L-form of Staphylococcus aureus adapted to a brain heart infusion medium without osmotic stabilizers

An L-form derived from halotolerant Staphylococcus aureus Tasaki was adapted to growth in a brain heart infusion medium without any supplemental osmotically protective solutes (360 mOsm/kg). This L-form had no chemically detectable peptidoglycan residues on its surface. Electron microscopic observations confirmed morphologically the absence of the structures and also of other osmotically protective polymers within or exterior to the cytoplasmic membrane. The osmotic stability and susceptibility to bacitracin, D-cycloserine, and vancomycin of the L-form adapted to growth in 360 mOsm osmotically unprotective medium was higher than that of the L-form grown in 1,950 mOsm supplemented with 4.5% NaCl. The adapted L-form tended to be more sensitive to almost all of the antibiotics examined, other than the inhibitors for cell wall-synthesis, than the original L-form strain requiring osmotic protection for growth. Chemical analysis of the membrane of the adapted L-form indicated 16.3% total lipids and 20.6% proteins by dry weight of the membrane, and it contained larger amounts of lipid phosphorus (20.0 microgram/mg).

Growth and division of spiroplasmas: morphology of Spiroplasma citri during growth in liquid medium

The helical mycoplasma Spiroplasma citri was examined by electron microscopy with a newly developed transfer technique which preserves the helical morphology of the organism. The smallest viable cell was found to be a two-turn (elementary) helix. During the logarithmic phase of growth, organisms increased in length and divided by constriction, liberating two-turn elementary helices. The most frequently dividing parental helix was one with approximately four turns, yielding two elementary helices. Influence of pH and temperature on the morphology of the organism was also investigated. In unbuffered medium, growth of the organism produced a significant decrease in pH and a consequent formation of abnormal morphological forms and cell lysis. At 37 degrees C, cell division was inhibited, leading to a progressive disappearance of two-turn helices and an increase in the average length of other helices. Finally, helices were never seen to arise from round bodies at any stage of the growth cycle.