You’ll find Gigi’s comment about bacteria throughout the soil science literature, but the first article I tracked down on the subject suggests that pristine soil can have up to a million species of bacteria (Gans, Wolinsky and Dunbar; Science August 26, 2005. Vol. 309, pp. 1387-1390).
Answers to yesterday’s question: (1) fruit espalier along the fence and (2) planted in a guild with bulbs; (3) chicken tractor; (4) pool converted to a natural swimming pond, fed by (5) rooftop catchment (6) filtering through a constructed wetland; (7) potatoes growing in stacked tires filled with straw; (8) an herb spiral; (9) keyhole beds (10) polycropped with garlic and salad greens.