Bacteria Colon Community modelling Forecasting Gastrointestinal Microbiome Humans Hydrogen Hydrogen sulphide Important features Metabolic parameters Metabolism Metabolites Methane Methanogens Microbial communities Microbiome Models, Biological Predictive analytics Relative abundance Short-chain fatty acids Spatial representations Sulfides Sulfur compounds Sulphate-reducing bacteria Sulphide concentration Volatile fatty acids bacterium biological model colon human