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Microcysts of the cellular slime mold Polysphondylium pallidum. I. Factors influencing microcyst formation
Abstract:
Microcyst formation can be induced by increasing the osmotic pressure of the surrounding medium. Certain ions such as K(+), Ca(++), or Mg(++) may be needed in the encystment process, and the presence of divalent cations increases the rate of encystment and cyst maturation. Chloride of potassium is optimal for encystment, but other anions of potassium are either less effective or toxic. The optimal pH for encystment was found to be pH 6.0. The use of agar plates containing KCl revealed the importance to the encystment process of inhibiting cell aggregation. When myxamoebae of Polysphondylium pallidum strain Pan-17 are deposited on KCl-agar plates, approximately 20% of the population proceeds through aggregation to sorocarp formation at the concentration of KCl optimal for microcyst formation. However, the same proportion of myxamoebae remains unaligned, or forms defective aggregation centers, if synergistic inhibitors (such as incubation in darkness or at low temperature) are employed in addition to KCl. The possibility that this is due to heterocytosis has been excluded. Accordingly, it is suggested that during the stationary phase approximately 20% of the population becomes committed to forming component cells of fruiting bodies, and that these myxamoebae cannot be induced to form microcysts by exposure to KCl. In P. pallidum strains WS-320 on the other hand, the imposition of synergistic inhibitors leads to the total encystment of the cell population. This suggests that, in contrast to Pan-17, the myxamoebae of the latter strain remain potentially equal and exhibit minimal presumptive specialization.
Insights
Microcyst formation in Polysphondylium pallidum is induced by osmotic pressure, with potassium chloride being optimal. Strain Pan-17 shows partial resistance to microcyst induction due to cell specialization, unlike strain WS-320.
Area of Science:
- Cell Biology
- Developmental Biology
- Microbiology
Background:
- Microcyst formation is a crucial survival mechanism for certain microorganisms.
- Osmotic pressure and specific ions play significant roles in inducing encystment.
- Polysphondylium pallidum is a model organism for studying cellular differentiation and development.
Purpose of the Study:
- To investigate the optimal conditions for microcyst formation in Polysphondylium pallidum.
- To explore the role of osmotic pressure and specific ions, particularly potassium chloride (KCl), in inducing encystment.
- To understand the differential response of various strains, such as Pan-17 and WS-320, to encystment-inducing conditions.
Main Methods:
- Inducing microcyst formation by increasing osmotic pressure using KCl-agar plates.
- Optimizing encystment conditions, including ion type, pH, and synergistic inhibitors (darkness, low temperature).
- Analyzing the aggregation and encystment patterns of Polysphondylium pallidum strains Pan-17 and WS-320.
Main Results:
- Optimal microcyst formation occurs at pH 6.0 with potassium chloride (KCl) as the inducing agent.
- Strain Pan-17 exhibits approximately 20% resistance to KCl-induced encystment, attributed to pre-committed cells forming fruiting bodies.
- Strain WS-320 shows complete encystment under synergistic inhibitory conditions, indicating less presumptive cell specialization.
Conclusions:
- Potassium chloride (KCl) is an effective inducer of microcyst formation in Polysphondylium pallidum.
- Cellular commitment to differentiation pathways can influence the success of encystment induction.
- Strain-specific differences in cell specialization affect the population's response to environmental cues for survival.