Since few months, I have started working in bacterial bioflocculation experiment with 5 screened strains. I've successfully characterized the first strain; whereas 4 other screened strains are stored under ultra-low temperature. This unpredictable behavior started from the next strains under characterization process. The polymer/product concentration as well its activity started varying in each time of experiment get repeated. So, I’m wondering how this happened with my screened bacterial strains and when things were done so precisely in every step? If anyone can explain this and suggest if something has been lacking or been overlooked in the process, I would greatly appreciate it.