Heat the oven to 400 F. Have ready a nonstick baking sheet.
In a bowl, combine the flours, wheat germ, baking soda and salt. Whisk to blend. Add buttermilk and egg and stir just until moistened. The dough will be sticky.
Turn the dough out onto a generously floured work surface and, with floured hands, gently knead it 8 to 10 times. Gather into a loose ball.
On the baking sheet, form the dough into a 7-inch round. Dust the top of dough with a small amount of flour. Cut a large (4-inch) X into the top of the dough, cutting about 1/2 inch deep.
Bake until the bread splits open at the X and makes a hollow sound when the underside is tapped, 25 to 30 minutes. Transfer to a wire rack and let cool for 2 hours (ideally) before slicing.