The rest are all hitch-hikers, mainly harmless bacteria that have evolved with us.

其它的都是搭便车的生物，主要是一些与我们共生的无害细菌。

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Put simply, probiotics are harmless bacteria that help protect the human body from harmful bacteria.

简单地说，益生素是无害的细菌，能保护人体免遭有害细菌的侵袭。

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Scientists at the University of Birmingham have shown that harmless bacteria that feeds on sugar produces hydrogen gas.

伯明翰大学的科学家发现，以糖为生的无害细菌能产生氢气。

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They may even use harmless bacteria as a transport link to arm other harmful bugs that pass by.

FORBES: Germ Warfare

The harmless bacteria - belonging to the Bacillus genus - then feed on the nutrients to produce limestone.

BBC: Key test for re-healable concrete

There is no need to panic, however: the creatures in question are harmless bacteria that were found preserved in a crystal of rock salt.

ECONOMIST: Old salts