Nobel Prize laureate Monod proposed the Monod equation to model the growth of microorganisms. The equation is dependent mainly upon an organism's maximum growth rate and the concentration of a limiting substrate.

To find a microorganism's growth rate, the term for the limiting substrate needs to be constant, which led to the development of the chemostat.

Larsen and Dimmick described a correlation between biofilm growth and the surface area-to-volume ratio. This is based on the fact that, as the volume of an object decreases, the proportion of the surface area compared to the volume increases. In microchemostats with very low working volumes, this means there will be a higher proportion of surface-adhering bacteria compared to free-floating bacteria, facilitating biofilm formation.

Topiwala and Hamer developed a mathematical model to determine factors that disrupt a bioreactor’s optimal function. Their model describes bacterial growth in a liquid culture when an additional culture forms along the bioreactor walls. They found that wall growth expands the operational range of the liquid culture within the bioreactor, delaying washout until a significantly higher dilution rate is reached.

Elowitz et al. and Atkinson et al. both developed oscillators using synthetic gene networks. To create an oscillatory gene circuit, they utilized two types of genes: activators and repressors. By engineering gene circuits with activators and repressors, they generated systems with oscillatory gene expression.

Elowitz et al. and Atkinson et al. developed similar genetic circuits, aiming to induce oscillatory behavior in gene expression (which is based on protein production within a cell). In contrast, this study demonstrates intercellular, oscillatory behavior in cell growth and population dynamics.

You et al. demonstrated the functionality of a genetic circuit to regulate communication and population in E. Coli on a macroscopic scale. They expected the circuit to perform similarly when scaled down the microscopic level. Balagadde et al. used this circuit as a benchmark for their microchemostat by demonstrating consistent and stable oscillations in E. Coli populations over extended periods.

You et al. successfully demonstrated and described a genetic circuit to consistently regulate communication and cell death in E. Coli. This circumvents differences the bacteria can exhibit though mutations, which would lead to further differences within a population. This genetic circuit was used in the experiment described in Figure 3.

Starting with Kim and Lee (reference 8), researches are pushing towards smaller, more compact bioreactors for the benefits of miniaturization, which include using less resources, reduced costs, and benefiting from physics at the micro/nano scale.

In the observations of Costerton et al., they have found the surface adhering bacteria making up biofilms differ physically to their free-floating counterparts.

Zanzotto et al. developed a microscopic bioreactor with a gas permeable membrane for carrying out bacterial fermentation. Their device mirrors the functionality of larger bioreactors and as an early showcase of bioreactor miniaturization.

Miller and Bassler described quorum sensing in bacteria and other microorganisms to coordinate activity. The key takeaway of the paper is quorum sensing is dependent upon population density to regulate gene expression.

Costerton et al. provided a detailed description of microbial biofilms through their own experiments and observations. They have found biofilms can form in any sufficient aquatic environments and have distinct properties compared to free-floating bacteria of the same species.

The last point poses a problem, since the study of a strain of bacteria can be influenced by the bacteria in biofilms.

The Larsen's and Dimmick's experiments determined the existence biofilms in early chemostats through observing microbial populations with different parameters, such as temperature, dilution rate, and different species of bacteria.

Their paper was published in the 1960s, in which the chemostats of the time were larger, made from glass, and had macro-scale elements, such as vaccine stoppers or separate inlets for bacterial cultures. One conclusion reached is the presence of biofilms increase with a smaller chemostat.

Zanzotto et al had developed a microscopic bioreactor for carrying out bacterial fermentation. Their device had sensors measuring 2 mm in diameter and can hold a volume as low as 5 µL, compared to the 500 mL of a typical bioreactor.

Here, the authors further miniaturized their bioreactor volume down to the nanoliter range/scale. For reference, 1 microliter is one millionth of a liter, while 1 nanoliter is one billionth of a liter.

Research from as early as the 1950s has found that different properties of bacteria can be studied by creating a stable environment with a constant source of nutrients. This has been backed up with mathematical models and led to the creation of the chemostat.

Novick and Szilard developed the first chemostat. This allowed them and other researchers to study the metabolism, regulatory processes, adaptations, and mutations of bacteria / microorganisms.