Kinetic modeling of Shewanella baltica KB30 growth on different substrates through respirometry

Abstract

Background: Shewanella baltica KB30 was isolated from seawater collected in Kandalaksha Bay, White Sea (Russia). This strain is known for its ability to grow on a pool of different substrates, including carbohydrates, carboxylic and amino acids, and lipids. However, no data are available on its metabolic efficiency in relation to the use of different carbon sources typologies. This work represents the first attempt to characterize S. baltica by its heterotrophic kinetic performance.

Results: Growth and substrate consumption, during the biodegradation of sodium acetate, glucose, tween 80 and peptone, were analyzed through a respirometric method. To find the model best fitting the experimental data and to obtain the kinetic parameters, the equations of Monod, Moser, Contois and Tessier were applied. The kinetic behavior of S. baltica was fitted to Monod model for sodium acetate and tween 80, while it was adjusted to Contois model for glucose and peptone. In this regard, peptone was consumed faster than the other substrates, as indicated by the highest values of substrate degradation rate, which exceeded 60 mg O₂ L^-1 h^-1.

Conclusions: Proteolytic metabolism was favored than lipidic and glucidic metabolism, which could contribute much more to mineralization and recycling of proteins than lipids and carbohydrates.

Keywords: Carbon utilization; Kinetics; Modeling; Shewanella baltica.

Fig. 1

Schematic diagram of the bioreactor used in the respirometric experiments (a); evolution of dissolved oxygen (DO) (b) and schematic diagram of the assessment of the kinetic parameters for the biodegradation of different substrates by Shewanella baltica KB30: yield coefficient (Y), substrate concentration S, biomass concentration (X), oxygen consumption (OC), maximum specific growth rate (µ_m), empirical specific growth rate (µ_emp), dynamic oxygen uptake rate (R_s) and substrate half-saturation coefficient (Ks) (c)

Fig. 2

Time course of dissolved oxygen (DO) in a typical respirometric experiment carried out with Shewanella baltica KB30 for the metabolization of the selected substrates: sodium acetate (a), glucose (b), tween 80 (c) and peptone (d)

Fig. 3

Degrading ability of Shewanella baltica KB30 regarding different substrate categories (carbohydrates, carboxylic and amino acids, amine/amides and lipids), as previously determined by the Biolog Microarray system. Arrows’ thickness is proportional to the number of substrates used for each category

Fig. 4

Substrate degradation rate (r_su) of Shewanella baltica KB30 during the respirometric experiments in relation to substrate concentration (S), measured as chemical oxygen demand in (mg O₂ L⁻¹), obtained by different models: Monod (a), Moser (b), Contois (c) and Tessier (d)

Fig. 5

Cell growth rate (r_x) of Shewanella baltica KB30 during the respirometric experiments in relation to substrate concentration (S), measured as chemical oxygen demand in (mg O₂ L⁻¹), obtained by different models: Monod (a), Moser (b), Contois (c) and Tessier (d)