一種普通的磁性礦物——微小磁鐵礦(kuang)晶(jing)粒能同時充(chong)當(dang)電(dian)(dian)(dian)(dian)(dian)子受體(ti)和(he)電(dian)(dian)(dian)(dian)(dian)子給(gei)體(ti)的角色，從(cong)而像(xiang)電(dian)(dian)(dian)(dian)(dian)池一樣(yang)工作。他讓由地桿菌(jun)屬(shu)(shu)和(he)紅假(jia)單(dan)胞菌(jun)屬(shu)(shu)組成的群(qun)落生長在(zai)磁(ci)鐵上面(mian)，然后發現(xian)地桿菌(jun)屬(shu)(shu)能將電(dian)(dian)(dian)(dian)(dian)子投(tou)放(fang)到晶(jing)體(ti)上，而紅假(jia)單(dan)胞菌(jun)屬(shu)(shu)從(cong)晶(jing)體(ti)上獲取電(dian)(dian)(dian)(dian)(dian)子。對于群(qun)落而言(yan)，磁(ci)鐵礦(kuang)晶(jing)體(ti)就像(xiang)的可充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池一樣(yang)發揮(hui)作用：由地桿菌(jun)屬(shu)(shu)充(chong)電(dian)(dian)(dian)(dian)(dian)，紅假(jia)單(dan)胞菌(jun)屬(shu)(shu)耗電(dian)(dian)(dian)(dian)(dian)。依據的不同需求，磁(ci)鐵可以(yi)作為一種導體(ti)，也可以(yi)是(shi)電(dian)(dian)(dian)(dian)(dian)子的儲存箱和(he)來(lai)源。