High diversity on a single grain of soil

Why can a single grain of soil nevertheless have hundreds of species on them? One reason is “microbial warfare”, where microbes continuously try to kill one another by producing toxins. By trying to be one step ahead of the others, there is an ongoing fight. But what if they become resistant to each other’s toxins? Why not just lose the toxin, which after all is pretty costly to produce? As it turns out, horizontal gene transfer (HGT) saves the day, and nevertheless maintains diversity on a single grain of soil: