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Isolation and characterization of nonspreading mutants of the gliding bacterium Cytophaga johnsonae
Abstract:
Three approaches were taken to isolate a total of 153 nonspreading mutants derived from our laboratory strain of Cytophaga johnsonae, UW101, or from its auxotrophic derivative, UW10538. Characterization of 109 of these mutants led to their placement in five general categories: (i) motile, nonspreading (MNS) mutants whose cells are motile to various degrees but whose colonies fail to spread on agar gels under any conditions of incubation; (ii) conditional nonspreading (CNS) mutants with motile cells whose colonies require more moisture to spread on agar gels than do those of wild-type cells; (iii) filamentous conditional motility (FCM) mutants whose cells grow as nonmotile filaments or as motile cells with wild-type morphology, depending on conditions of incubation; (iv) short, tumbling, nonspreading (STN) mutants with short cells that tumble constantly; and (v) truly nonmotile (TNM) mutants whose cells never move and whose colonies never spread under any conditions tested. All TNM mutants exhibited a remarkable pleiotropy not seen in the other four classes of mutants: all were resistant to 39 phages to which wild-type cells are sensitive, and all were unable to digest chitin, which is digested by wild-type cells. The correlation between ability to move and phage sensitivity was strengthened further by showing that 150 additional TNM mutants derived from UW101 and 43 TNM mutants derived from 29 independent isolates of C. johnsonae were resistant to all phages to which their parents were sensitive. Furthermore, motile revertants of TNM mutants became phage sensitive, and temperature-sensitive mutants were motile and phage sensitive at 25 degrees C and nonmotile and phage resistant at 32 degrees C. Evidence supports the conclusion that any mutation rendering cells truly nonmotile invariably alters cell surface-associated properties such as phage sensitivity and chitin digestion merely as a consequence of changing a moving cell surface to a static surface.
Insights
Researchers isolated 153 Cytophaga johnsonae mutants, categorizing them by motility and colony spreading. Truly nonmotile mutants showed pleiotropy, losing phage sensitivity and chitin digestion abilities.
Area of Science:
- Microbiology
- Bacteriology
- Genetics
Background:
- Cytophaga johnsonae is a motile bacterium known for its spreading colonies on agar.
- Understanding the genetic basis of motility and colony spreading is crucial for bacterial research.
Purpose of the Study:
- To isolate and characterize nonspreading mutants of Cytophaga johnsonae.
- To investigate the relationship between cell motility, colony spreading, and other cell surface properties.
Main Methods:
- Isolation of 153 nonspreading mutants using three different approaches.
- Categorization of 109 mutants into five classes based on motility and spreading.
- Phenotypic characterization including motility assays, spreading assays, phage sensitivity tests, and chitin digestion assays.
Main Results:
- Five classes of mutants were identified: motile nonspreading (MNS), conditional nonspreading (CNS), filamentous conditional motility (FCM), short tumbling nonspreading (STN), and truly nonmotile (TNM).
- TNM mutants displayed pleiotropy, being resistant to phages and unable to digest chitin, unlike wild-type cells.
- Motility and phage sensitivity were correlated; motile revertants regained phage sensitivity, and temperature-sensitive mutants showed conditional motility and phage sensitivity.
Conclusions:
- Mutations rendering Cytophaga johnsonae cells truly nonmotile lead to altered cell surface properties, including phage resistance and reduced chitinase activity.
- These changes in surface properties are likely a consequence of the transition from a motile to a static cell surface.
- The study provides evidence for a link between motility and specific cell surface characteristics in C. johnsonae.