Errol, ....Serge, others...
Relating to your question about unu.ai, hivemind and your examples and question to Serge of, "How do you define 'think'?", below, please notice that I define 'think' and 'consciousness' as structural coding (or nested structural coding) which fits for all your microbial communications instances.
Also, please notice that the structural coding I generally refer to is in the energy-related ~6^n hydrogen-bonded ordered water stacks continually forming at aerobic respiration sites. Also, please notice that these sites, and thus the account I advocate and bring forward are INSIDE neurons (and other cells), thus differing a bit from the neuron theory model which Jonathan and many others may advocate. Also please note the nested organization of: ordered water structures (and energy) within respiration sites within neurons within brain structures within environmental vibrations within hivemind conveyed within protein folding markings in the English language words and sentences resonating here within our various screens, etc..
The thing with this structural coding within the respiration reaction is it is integrated with energy collection and conservation and thus structural codings which associate with energy conservation, and/or associated development of what we call enzymatic structures which replicate DO have or offer some survival or sustenance advantage. And, this structural coding advantage, if you think about it, is also quite a bit like the value we find in the empirical 'proofs' of our so-called objective science. Things that strongly repeat and also conserve energy generally have value and/or persist and re-occur.
[As an aside, please notice that the storyline I am advocating, including the 6^n structural coding in water forming in the respiration reaction and besides also demonstrating multiple states and variable mass density in increments of 1/2 spins, flows from empirical 'proof' or basis found in the analog math of magnetic tetrahedron. Learning the analog math IS acquiring physical intuition via the tactile channel on the things listed herein.]