Selection of microbial mutants tolerant to extreme environmental stress using continuous culture-control design

The design of controllers for a continuous selection technique (BOICS; Brow n and Oliver, 1982) is considered. This technique is used to obtain microbi al mutants that are tolerant to extreme environmental stress. Applications of BOICS have been hampered by the problem of controller design. In this pa per, a modified implementation of BOICS is considered which has a number of practical advantages. A model-based approach to controller design is taken . The case in which the stress is due to an inhibitory substance in the gro wth environment is considered. The analysis is intended to be applicable to any reasonable combination of organism and inhibitor. Conventional linear and time-invariant controllers are considered. Guidelines for the selection of controller parameters' values are suggested. The application of these g uidelines requires that certain process parameters' values be identified. M ethods by which these parameters' values can be identified are suggested. S imulation results indicate that the resulting controllers perform satisfact orily. This is confirmed by experimental data from a model selection experi ment. A recipe for the design of controllers is a necessary part of a proto col for BOICS. It is hoped that the solution to the controller design probl em that is offered in this paper will encourage further applications for th e technique.