Microbes are simple microscopic organisms that lack the ability to sustain a fully functional and capable nervous system.
Cooperation [ability of two individuals to interact with each other, which results in a net gain] is not performed with the help of the nervous system. Instead, it is required for supporting the needs of either one's own body or the other organism.
Cooperation can be performed in the absence of the nervous system as it requires coordinated working between two individuals and the gain of benefits from the help provided.
Cooperation [coordination] among the organisms is based on their ability to provide support or benefits and take the same when the need arises. It can be done in the absence of the nervous system as well.