A simple, fast and inexpensive approach using <i>E. coli</i> to detect and estimate vitamin B12 content in microbial extracts

Vitamin B12 is an essential micronutrient produced only by prokaryotes, and animals must acquire it from their diet. Vitamin B12 is critical for the synthesis of methionine and propionyl-CoA metabolism. In humans, vitamin B12 deficiency has been linked to many disorders, including infertility and developmental abnormalities. The growing trend towards plant-based diets and ageing populations increases the risk of vitamin B12 deficiency, and, therefore, there is an increasing interest in understanding vitamin B12 biology. Accurate approaches for detecting and quantifying vitamin B12 are essential in studying its complex biology, from its biogenesis in Bacteria and Archaea to its effects in complex organisms. Here, we present an approach using the commonly available E. coli methionine auxotroph strain B834 (DE3) and a multi-well spectrophotometer to detect and estimate the levels of vitamin B12 from biological samples at picomolar concentrations. We further show that our method is sufficient to reveal important differences in the production of vitamin B12 from vitamin B12-synthesising bacteria commonly found in the microbiome of wild Caenorhabditis elegans isolates. Our results establish a high-throughput and simple assay platform for detecting and estimating vitamin B12 levels using the E. coli B834 (DE3) strain.