A modified procedure for determining the pattern of peptidoglycan synthesis during the division cycle has allowed the measurement of the rate of side wall synthesis during the division cycle without the contribution due to pole formation. As predicted by a model proposing that the surface growth of the cell is regulated by mass increase, we find a decrease in side wall synthesis in the latter half of the division cycle. This supports the proposal that, upon invagination, pole growth accommodates a significant proportion of the increasing cell mass and that residual side wall growth occurs in response to the residual mass increase not accommodated by pole volume. The observed side wall synthesis patterns support the proposal that mass increase is a major, and possibly sole, regulator of bacterial surface increase. Membrane synthesis during the division cycle of the gram-negative, rod-shaped bacteria Escherichia coli and Salmonella typhimurium has also been measured with similar methods. The rate of membrane synthesis-measured by incorporation of radioactive glycerol or palmitate relative to simultaneous labeling with radioactive leucine exhibits the same pattern as peptidoglycan synthesis. The results are compatible with a model of cell surface growth containing the following elements. (i) During the period of the division cycle prior to invagination, growth of the cell occurs predominantly in the side wall and the cell grows only in length. (ii) When invagination begins, pole growth accommodates some cytoplasmic increase, leading to a concomitant decrease in side wall synthesis. (iii) Surface synthesis increases relative to mass synthesis during the last part of the division cycle because of pole formation. It is proposed here that membrane synthesis passively follows the pattern of peptidoglycan synthesis during the division cycle.How is the rate of cell surface synthesis regulated in bacteria? One proposal consistent with the available data is that the surface of the gram-negative, rod-shaped cell grows in response to the increase in cell mass. This proposal has been termed the surface stress model (12; see reference 13 for discussion and recent references). The continuous increase in the cytoplasmic constituents of a cell (RNA, protein, water, and ions, etc.) leads to an increase in turgor pressure on the cell surface. This increase in turgor pressure leads to the stressing and bending of peptidoglycan bonds. The cell surface expands when nascent material is incorporated into the stress-bearing plane upon the preferential scission of the stressed peptidoglycan linkages. Thereby, new wall growth responds to and accommodates the increase in mass or volume. The slight reduction in turgor resulting from the incorporation of new material into the stressed layer allows cell mass to again increase prior to further surface growth. The continuous and exponential increase in cell mass or cytoplasm leads to the continuous increase in cell surface.It has been proposed that the murein of gram-negative, rod-shaped bacteria...

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Bob Feilden will be remembered by scientists and engineers around the world for his innovative work on industrial gas turbines which became, in the Ruston Type TAgas turbine, a prime mover of choice for all those who wanted high reliability and automatic or remote operation.