Methods for fluid mixing systems with laterally displaced flexible drive lines

A method for mixing a biological suspension, the method comprising:

• disposing a biological suspension within a compartment of a container, the biological suspension comprising cells or microorganisms suspended within a nutrient growth medium;
• and
• rotating a first drive line and laterally spaced apart second drive line within the compartment of the container so as to cause the drive lines to twist around each other to thereby transition from a non-helical configuration into a helical configuration and mix the biological suspension, wherein the drive lines are configured to transition between the non-helical configuration and the helical configuration by twisting and untwisting, wherein the non-helical configuration comprises the first drive line and the second drive line arranged parallel to each other, and the helical configuration comprises the first drive line and second drive line arranged around each other in a double helix.