Experimental molecular evolution showing flexibility of fitness leading to coexistence and diversification in biological system

Molecular evolution was observed through three serial cycles of consecutive random mutagenesis of glutamine synthetase gene and chemostat culture of transformed Escheiichia coli cells containing the mutated genes. From an initial of diversified mutant population in each cycle, several varieties of mutants reached the state of coexistence. In addition, a once extinct mutant gene was found to have the capacity to coexist with a gene pool of later cycle of molecular evolution. These results including the kinetic characteristics of the purified wild-type and mutant glutamine synthetases in the phylogenetic tree revealed that the enzyme activity has diverged rather than optimized to a fittest value during the course of evolution. Here, we proposed that the flexibility of the fitness of a gene in consequence to cellular interaction via the environment is an essential mechanism governing molecular evolution.