The role of bias in crystallization conditions in automated microseeding

The automated microseeding protocol previously proposed by D'Arcy et al. [D'Arcy et al. (2007), Acta Cryst. D63, 550-554] includes an inherent chemical shift in all conditions in a sparse-matrix screen. This results from the uniform addition of mother liquor used to stabilize the microcrystalline seed stock, which is usually the mother liquor that resulted in successful crystal growth. It was found that there is an overlap in identified crystallization leads between addition of seed and addition of the mother liquor used to stabilize the seed. This indicates that additional crystallization `hits' primarily (but not exclusively) arise from changes in the drop composition, not the introduction of seeds. A complementary automated microseeding protocol is proposed as a novel approach for biasing drops in a screen with many of the most popular precipitants.