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Role of autocide AMI in development of Myxococcus xanthus
1Department of Microbiology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
Abstract:
A new developmental mutant of Myxococcus xanthus has been isolated by screening TnV insertion mutants for AMI-dependent development in submerged culture. This mutant (ER304) aggregated and sporulated on agar surfaces but required at least 3.8 micrograms of autocide AMI per ml for development in submerged cultures. Spore rescue of ER304 was obtained with the saturated, monounsaturated, and diunsaturated fatty acid fractions of AMI, with specific activities of 68, 115, and 700 U/mg, respectively. In addition, several model fatty acids were capable of rescuing sporulation of ER304; however, there was no correlation between specific lytic activity observed in vegetative cultures and specific rescue activity. Rescue of ER304 was effected during the first ca. 12 h after the initiation of starvation conditions; after this time, addition of AMI or model fatty acids killed the cells. Supernatant fluids of ER304 rescued development in dsg mutants (e.g., DK3260) in submerged cultures, but dsg mutant supernatant fluids were incapable of rescuing ER304 development. The data presented in this article support the idea that the primary mechanism of rescue by AMI is not via lysis, although developmental lysis may be an indirect result of the rescue event. A membrane permeability model is presented to explain the role of autocides in early developmental events in wild-type strains and in the aggregation and sporulation rescue of developmental mutants ER304 and DK3260.
Insights
A new Myxococcus xanthus mutant requires autocide AMI for development in liquid cultures. Fatty acids in AMI rescue this mutant, suggesting a membrane permeability role in development, not lysis.
Area of Science:
- Microbiology
- Developmental Biology
- Bacterial Genetics
Background:
- Myxococcus xanthus undergoes complex developmental processes, including aggregation and sporulation.
- Autocides, such as AMI (autocide molecule I), play a role in M. xanthus development, but their precise function is not fully understood.
- Developmental mutants often exhibit defects in these complex life cycle transitions.
Purpose of the Study:
- To isolate and characterize a novel developmental mutant of Myxococcus xanthus dependent on autocide AMI for development in submerged culture.
- To investigate the role of AMI and its components in rescuing developmental defects.
- To elucidate the mechanism by which autocides influence M. xanthus development.
Main Methods:
- Screening of TnV insertion mutants for AMI-dependent development in submerged culture.
- Characterization of a new mutant (ER304) for aggregation and sporulation capabilities.
- Testing the rescue activity of AMI fractions and model fatty acids on mutant ER304 development.
- Analysis of supernatant fluids from wild-type and mutant strains for rescue capabilities.
- Development of a membrane permeability model.
Main Results:
- A new mutant, ER304, was isolated, requiring AMI for development in submerged culture but not on agar.
- Saturated, monounsaturated, and diunsaturated fatty acid fractions of AMI, as well as several model fatty acids, rescued ER304 sporulation.
- No correlation was found between lytic activity and rescue activity of fatty acids.
- Rescue was time-dependent, with addition of AMI or fatty acids becoming toxic after 12 hours of starvation.
- ER304 supernatant rescued dsg mutants, but not vice versa, indicating a specific role for ER304-produced factors.
Conclusions:
- The primary mechanism of AMI-mediated rescue in M. xanthus development is likely related to membrane permeability, not lysis.
- Autocides play a crucial role in early developmental events, influencing aggregation and sporulation in both wild-type and developmental mutants.
- The study presents a membrane permeability model to explain autocide function in M. xanthus development.