Reproducibility, the ability to carry out and replicate the results of a single experiment, is an important aspect of scientific disciplines. However, in the life sciences, the concept of reproducibility has become a large problem. A vast number of experiments throughout the various disciplines of the life sciences are seen to lack a reproducible nature, ultimately costing and inadvertently wasting large sums of money. Synthetic biology is no exception to the troubles of reproducibility, with inaccurate part characterisation impacting the the ability to use Bio-Design Automation (BDA) to build fully functioning, novel synthetic gene circuits.

iGEM devised the inter-lab study – an annual, large-scale study carried out by institutions around the world by researchers of varying experience levels – to determine the reproducibility of individual synthetic biology protocols, assessing and addressing the limiting factors of reproducibility. The study attempted to address variation between different models of plate readers by producing a step by step protocol for measurement and analysis, allowing the production of directly comparable fluorescence measurements. In addition, ribosome binding site (RBS) sequences designed to increase precision of expression were included in the devices to be transformed into the host cells.

A weakness in the measurement of fluorescence relative to OD600, as with previous IGEM interlab protocols, is the potential discrepancy between optical density and actual cell concentration. This year the IGEM study aims to reduce lab-to-lab variability further by measuring GFP fluorescence relative to absolute cell counts or colony forming units. Normalisation of fluorescence to colony forming units goes further by allowing measurement of fluorescence relative only to viable cells, and thus a more accurate measurement of promoter strength, whereas OD600 and absolute cell count measures cannot differentiate between viable and non-viable cells.