translation.en: These bacteria were not uncovered sooner because they are also among the smallest of all Earth's organisms -- so minute that they cannot be seen with conventional optical microscopy.
translation.zh: 我们没能在更早的时候发现这些细菌 是因为它们也是地球上体型最小的生物之一 你用普通的光学仪器是难以看得到它们的