Computational resources and strategies to construct single-molecule metabolic models of microbial cells.

Recent computational methodologies, such as individual-based modelling, pave the way to the search for explanatory insight into the collective behaviour of molecules. Many reviews offer an up-to-date perspective about such methodologies, but little is discussed about the practical information requirements involved. The biological information used as input should be easily and routinely determined in the laboratory, publicly available and, preferably, organized in programmatically accessible databases. This review is the first to provide a systematic and comprehensive overview of available resources for the modelling of metabolic events at the molecular scale. The glycolysis pathway of Escherichia coli, which is one of the most studied pathways in Microbiology, serves as case study. This curation addressed structural information about E. coli (i.e. defining the simulation environment), the reactions forming the glycolysis pathway including the enzymes and the metabolites (i.e. the molecules to be represented), the kinetics of each reaction (i.e. behavioural logic of the molecules) and diffusion parameters for all enzymes and metabolites (i.e. molecule movement in the environment). Furthermore, the interpretation of relevant biological features, such as molecular diffusion and enzyme kinetics, and the connection of experimental determination and simulation validation are detailed. Notably, the information from classical theories, such as enzymatic rates and diffusion coefficients, is translated to simulation parameters, such as collision efficiency and particle velocity.

Metabolic potential of the moderate halophile Yangia sp. ND199 for co-production of polyhydroxyalkanoates and exopolysaccharides.

Yangia sp. ND199 is a moderately halophilic bacterium isolated from mangrove samples in Northern Vietnam, which was earlier reported to grow on several sugars and glycerol to accumulate poly(hydroxyalkanoates) (PHA). In this study, the potential of the bacterium for co-production of exopolysaccharides (EPS) and PHA was investigated. Genome sequence analysis of the closely related Yangia sp. CCB-M3 isolated from mangroves in Malaysia revealed genes encoding enzymes participating in different EPS biosynthetic pathways. The effects of various cultivation parameters on the production of EPS and PHA were studied. The highest level of EPS (288 mg/L) was achieved using sucrose and yeast extract with 5% NaCl and 120 mM phosphate salts but with modest PHA accumulation (32% of cell dry weight, 1.3 g/L). Growth on fructose yielded the highest PHA concentration (85% of CDW, 3.3 g/L) at 90 mM phosphate and higher molecular weight EPS at 251 mg/L yield at 120 mM phosphate concentration. Analysis of EPS showed a predominance of glucose, followed by fructose and galactose, and minor amounts of acidic sugars.

Single Molecule Simulation of Diffusion and Enzyme Kinetics.

This work presents a molecular-scale agent-based model for the simulation of enzymatic reactions at experimentally measured concentrations. The model incorporates stochasticity and spatial dependence, using diffusing and reacting particles with physical dimensions. We developed strategies to adjust and validate the enzymatic rates and diffusion coefficients to the information required by the computational agents, i.e., collision efficiency, interaction logic between agents, the time scale associated with interactions (e.g., kinetics), and agent velocity. Also, we tested the impact of molecular location (a source of biological noise) in the speed at which the reactions take place. Simulations were conducted for experimental data on the 2-hydroxymuconate tautomerase (EC 5.3.2.6, UniProt ID Q01468) and the Steroid Delta-isomerase (EC 5.3.3.1, UniProt ID P07445). Obtained results demonstrate that our approach is in accordance to existing experimental data and long-term biophysical and biochemical assumptions.