PERIODIC, QUASI-PERIODIC, AND CHAOTIC COEXISTENCE OF 2 COMPETING MICROBIAL-POPULATIONS IN A PERIODICALLY OPERATED CHEMOSTAT

It is well known that when two microbial populations competing for a s ingle rate-limiting nutrient are grown in a chemostat with time-invari ant inputs, with competition being the only interaction between them, they cannot coexist, but eventually one of the two populations prevail s and the other becomes extinct. It has been suggested that periodic v ariation of one of the chemostat's operating parameters can stabilize the coexistence state of the two microbial populations. A systematic n umerical study of the model equations describing microbial competition in a chemostat with periodically varying dilution rate is performed, and it is shown that coexistence of the competing microbial population s is obtained for a wide range of operating conditions. The coexistenc e state is usually in the form of limit cycle oscillations. However, c ases of chaotic behavior resulting from successive period doublings an d quasi-periodicity are also observed.