Swarmer cell differentiation in Proteus mirabilis

Under the appropriate environmental conditions, the gram-negative bacterium Proteus mirabilis undergoes a remarkable differentiation to form a distinct cell type called a swarmer cell. The swarmer cell is characterized by a 20- to 40-fold increase in both cell length and the number of flagella per cell. Environmental conditions required for swarmer cell differentiation include: surface contact, inhibition of flagellar rotation, a sufficient cell density and cell-to-cell signalling. The differentiated swarmer cell is then able to carry out a highly ordered population migration termed swarming. Genetic analysis of the swarming process has revealed that a large variety of distinct loci are required for this differentiation including: genes involved in regulation, lipopolysaccharide and peptidoglycan synthesis, cell division, ATP production, putrescine biosynthesis, proteolysis and cell shape determination. The process of swarming is important medically because the expression of virulence genes and the ability to invade cells are coupled to the differentiated swarmer cell. In this review, the genetic and environmental requirements for swarmer cell differentiation will be outlined. In addition, the role of the differentiated swarmer cell in virulence and its possible role in biofilm formation will be discussed.     

Choline acetyltransferase activity of spinal cord cell cultures increased by co-culture with muscle and by muscle-conditioned medium

Activity of the enzyme choline acetyltransferase (CAT), which mediates the synthesis of the neurotransmitter, acetylcholine, was increased up to 20- fold in spinal cord (SC) cells grown in culture with muscle cells for 2 wk. This increase was directly related to the duration of co-culture as well as to the cell density of both the SC and muscle involved and was not affected by the presence of the acetylcholine receptor blocking agent, α-bungarotoxin. Glutamic acid decarboxylase (GAD) activity was often markedly decreased in SC-muscle cultures while the activities of acetylcholinesterase and several other enzymes were little changed. Increased CAT activity was also observed when SC cultures were maintained in medium which had been conditioned by muscle cells or by undifferentiated cells from embryonic muscle. Muscle-conditioned medium (CM) did not affect the activities of SC cell GAD or acetylcholinesterase. Dilution or concentration of the CM directly affected its ability to increase SC CAT activity , as did the duration and timing of exposure of the SC cells to the CM. The medium could be conditioned by muscle cells in the presence or absence of serum, and remained effective after dialysis or heating to 58 degrees C. Membrane filtration data were consistent with the conclusion that the active material(s) in CM had a molecular weight in excess of 50,000 daltons. We conclude that large molecular weight material that is released by muscle cells is capable of producing a specific increase in CAT activity of SC cells.     

Improved shoot regeneration system through leaf derived callus and nodule culture of Sansevieria cylindrica

Long-term culture establishment and efficient in vitro regeneration protocol for Sansevieria cylindrica Bojer ex Hook was developed using leaf derived callus and nodule culture. Profuse callus induction on leaf discs was achieved on Murashige and Skoog (MS) medium supplemented with 10 μM indole-3-butyric acid (IBA), while a high frequency of nodulation was induced on 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) containing media. Shoot regeneration ability from cultured tissues occurred at varying degrees on all media. Through callus culture a maximum of 17.6 ± 0.14 shoots per culture was formed on medium containing 5μM 6-benzyladenine (BA) and 2 μM α-naphthaleneacetic acid (NAA). Among nodule cultures, the 2,4-D generated nodules were more proliferative and regenerative as compared to 2,4,5-T induced nodules and a maximum of 25 ± 0.16 shoots per culture was produced on a medium containing 5 μM BA plus 1 μM NAA. The regenerated shoots were successfully rooted on a semi-solid half strength MS medium containing 5 μM IBA with an average root number 3.5 ± 0.18 and root length 6.5 ± 0.14 cm. The regenerative ability of callus tissues was steady upto one year, while the nodules retained the totipotency to regenerate on optimal medium even after 3 years of subculturing. The histological sections of nodules confirm the typical anatomy exhibiting the vascular elements in bundles with well demarcated cortex and epidermal covering.