Abstract
The incorporation of microbial diversity in design would ideally require predictive theory that would relate operational parameters to the numbers and distribution of taxa. Resource ratio-theory (RRT) might be one such theory. Based on Monod kinetics, it explains diversity in function of resource-ratio and richness. However, to be usable in biological engineered system, the growth parameters of all the bacteria under consideration and the resource supply and diffusion parameters for all the relevant nutrients should be determined. This is challenging, but plausible, at least for low diversity groups with simple resource requirements like the ammonia oxidizing bacteria (AOB). One of the major successes of RRT was its ability to explain the ‘paradox of enrichment’ which states that diversity first increases and then decreases with resource richness. Here, we demonstrate that this pattern can be seen in lab-scale-activated sludge reactors and parallel simulations that incorporate the principles of RRT in a floc-based system. High and low ammonia and oxygen were supplied to continuous flow bioreactors with resource conditions correlating with the composition and diversity of resident AOB communities based on AOB 16S rDNA clone libraries. Neither the experimental work nor the simulations are definitive proof for the application of RRT in this context. However, it is sufficient evidence that such approach might work and justify a more rigorous investigation.
Highlights
There is growing consensus on the key role of species richness of ecosystem function (Hooper et al, 2005; Cardinale et al, 2006)
In R3-high nitrogen and high oxygen (HNHO), the ammonia consumption was 22.3% ± 4.4% of the total ammonium concentration of the influent, while in R4-high nitrogen and low oxygen (HNLO) an average of 29.1% ± 4.4% of ammonium was removed after 28 days of operation
Free ammonia and free nitrous acid concentration were almost negligible in R1-low nitrogen and high oxygen (LNHO), while they varied over time in the other bioreactors (Fig. S2 and SI)
Summary
There is growing consensus on the key role of species richness of ecosystem function (Hooper et al, 2005; Cardinale et al, 2006). Empirical and theoretical studies in ecology suggest that elevated species richness improves ecosystem functional stability, especially system resilience to perturbations (Pimm, 1984; Tilman and Downing, 1994; Tilman et al, 2001). More diverse systems have a greater pool of physiological and genetic traits, which provide them the capacity to change and sustain function under varying environmental conditions. This observation is of particular relevance to the engineering of open biological systems. Wittebolle and colleagues (2009) argued that the initial evenness of the community rather than species richness per se is the key factor for the functional stability of the system. It seems likely that increasing microbial diversity will do no harm and may improve stability
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