You have to remember that the reactions that I show are "net" reactions. In reality, this is a much more complicated process. Some microorganisms are capable of initiating only a portion of the complete biodegradation. The first organism may take it halfway and then another type of organism will come along and consume the "intermediate product" that was formed from the first reaction to produce the final result, carbon dioxide (CO2). Some microorganisms are capable of mediating entire degradation from initial "reactant" to final "product". Others are only capable of completing a small fraction of the total degradation. That is why microbial "consortia" are usually better at degrading organics than individual species.