To explain the above, we consider recent results collected using a similar microfluidic perpendicular flow against a G. sulfurreducens EAB of approximately the same age (5 months), which provided evidence of compression due to pronounced elastic mechanical properties, compared to EABs of other ages, which could be studied by other onchip methods. We propose that the compression under the elevated perpendicular flow rates in the current work resulted in further improvement of the EET due to densification of cytochrome c charge carriers within the diminished EAB volume, thus further shifting the bottleneck further towards other (bio)chemical steps. As well, the expected deeper acetate penetration into the thick EAB at high concentration and high flow rate are expected to further reduce the distance required for EET between the active G. sulfurreducens bacteria (exposed to non-zero [Ac]) and the electrode surface. The reader is directed to the SI, where we present EIS results that support the hypothesis that increased flow rates and concentrations can reduce the ohmic resistances in our system. Again, we note that previous studies on reaction bottlenecks in EABs, had reported EET limitations throughout all monitoring times. We hypothesize that the shifted bottleneck reaction away from EET limitations in our highly matured EABs is because of the compression forces from the perpendicular flow orientation. This is in contrast to previous work where flow is directed tangentially, which will produce lift forces on the EAB, causing it to expand, which we posit will increase distances between charge carriers, resulting in bottlenecks in EET. To understand the differences in behaviour we propose future studies that focus on replicating the experimental conditions of the previous work (e.g., under tangential flow), this time in a system like the present one, with the present methods for control over temperature and applied potential, while also exploring the ability to conduct long-duration experiments on graphite electrodes. Previous demonstrations of accurate measurements into the EAB conductivity during growth may also provide complementary perspective that can lead to a better understanding of role of perpendicular versus tangential flow on EET. Next, we examine the data in Figure , which reports the effect of growth time, flow rate and acetate concentration on the product of the pre-exponential constant and the kinetic rate proportionality constant (A•p), as explained in relation to equation 2. This examination requires a kinetic formulation involving the rate-limiting bottleneck step. After 1 month, the limitations arising from EET are difficult to analyse because it is itself a complex process, involving electron transport through a series of sub-transport pathways, any of which may be the source of the limitation. Therefore, we do not consider the 1-month data in this analysis. However, after 4 months, EET is no longer the limiting mechanism, and we hypothesize that the limitation has switched to acetate oxidation.