The image above gives the general ranges of the organisms where you should also note the overlap in each group. I have come to see the transition zone from one group to the other as a "Problem Zone" where none of the individual groups is completely in its optimum growth range. Frequently we see this problem as increase in effluent suspended solids (TSS) for both the low and high temperatures. Also with low temperatures slowing metabolic activity in general, the low temperature problem zone also can cause problem with BOD/COD removal.
In my field of bioaugmentation or adding in select cultures to wastewater systems to enhance treatment, we add organisms that are very successful in the problem zone ranges to quickly establish the new microbial population that nature is taking its time to develop. By adding cultures, the system can be rapidly brought back under control for the entire period of high or low temperatures.