The bacterium is naturally present in large numbers in the intestine.这种细菌大量地自然存在于肠道内。Nitrates are chemicals that occur naturally in water and the soil.硝酸盐是水和土壤中自然存在的化学物质。Bacteria are naturally present in the environment.细菌自然存在于环境当中。Minerals occur naturally in the earth's crust.矿物自然存在于地壳中。