Author Order and Quality of Publication - Postdocs

Bob, a postdoc in Professor Jolly's Lab, initiates a research project consisting of isolating microorganisms that have a particular enzymtic activity against a target molecule. Bob is making excellent progress with the isolation of the microorganism, but Professor Jolly wants to reach a higher quality journal and with greater speed. In order to achieve these goals, Professor Jolly adds Susan, another postdoc, to the project. Susan has extensive experience in protein purification and characterization.

Bob accepts a position elsewhere after 12 months. He writes a paper based on the existing data, but it is not sufficient for the goals Professor Jolly has.

A few months later, another paper-- a full characterization of the molecurel--is written. Most of the data that ends up in the full paper has been generated by Susan. Susan also wrote a considerable part of the manuscript.

How should the decision about the order of authors be made?