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A bacterial factor induces changes in cysteine proteinase forms in the cellular slime mould Dictyostelium discoideum
1Department of Biological Science, University of Stirling, Scotland, U.K.
Abstract:
The electrophoretic pattern of cysteine proteinases in axenically grown myxamoebae of Dictyostelium discoideum can be altered by the addition of either Gram-negative (Klebsiella aerogenes, Escherichia coli) or Gram-positive (Micrococcus lysodeikticus, Bacillus subtilis) bacteria to the culture. No changes occurred, however, if either yeast or latex beads were used in place of bacteria. The changes involved the simultaneous loss of proteinases characteristic of the axenic cells (the A-forms) and the acquisition of those found in cells which have been grown on bacteria (the B-forms). Using K. aerogenes the conversion was complete within 4 h. Extracellular proteinase activity was unaffected during this period. After the D. discoideum cells had been lysed, no equivalent change in proteinase band pattern could be produced either by prolonged incubation of cell extracts or by treatment with proteinases. An identical conversion could be induced in cultures of myxamoebae by a factor, cysteine proteinase converting factor (CPCF), present in the 15,000 g supernatant of a sonicated suspension of K. aerogenes. CPCF was macromolecular, as demonstrated by both ultrafiltration and gel filtration, acid-precipitable, but was soluble in ethanol or alkali. Its activity was unaffected by treatment with trypsin. The results suggested that CPCF might be a component of the bacterial cell wall, and since its activity was affected by lysozyme treatment, peptidoglycan is implicated. The results can be interpreted in terms of a novel nutrient-dependent post-translational change which affected most of the cysteine proteinases present in D. discoideum myxamoebae.
Insights
Bacterial presence alters Dictyostelium discoideum cysteine proteinases, shifting from axenic (A-forms) to bacterial (B-forms) types. This nutrient-dependent change is mediated by a bacterial cell wall factor, cysteine proteinase converting factor (CPCF).
Area of Science:
- Cell Biology
- Biochemistry
- Microbiology
Background:
- Dictyostelium discoideum exhibits distinct cysteine proteinase patterns depending on its growth environment.
- Axenically grown myxamoebae possess specific proteinases (A-forms) different from those in bacteria-fed cells (B-forms).
Purpose of the Study:
- To investigate the environmental factors influencing cysteine proteinase expression in Dictyostelium discoideum.
- To identify the mechanism behind the shift in proteinase patterns observed between axenic and bacterial-fed cells.
Main Methods:
- Culturing Dictyostelium discoideum myxamoebae with various bacteria, yeast, and latex beads.
- Analyzing electrophoretic patterns of cysteine proteinases.
- Characterizing a bacterial factor (CPCF) responsible for inducing proteinase pattern changes.
Main Results:
- Addition of Gram-negative or Gram-positive bacteria, but not yeast or latex beads, induced a conversion from A-form to B-form proteinases within 4 hours.
- A macromolecular factor (CPCF) from Klebsiella aerogenes supernatant mediated this conversion.
- CPCF activity was linked to bacterial cell wall components, potentially peptidoglycan, and was trypsin-resistant but lysozyme-sensitive.
Conclusions:
- Bacterial interaction triggers a nutrient-dependent, post-translational modification of cysteine proteinases in Dictyostelium discoideum.
- CPCF, likely a bacterial cell wall component, plays a crucial role in this environmental adaptation.
- This study reveals a novel mechanism of gene expression regulation influenced by microbial cues.