The Impact of Bacterial Cell Growth and Microbial Lag on the Transport and Biodegradation of Organic Compounds

Abstract

Miscible-displacement experiments were conducted to examine the impact of microbial variables (such as cell growth and metabolic lag) on the biodegradation and transport of salicylate, a model hydrocarbon compound. For each experiment, a soil column was inoculated with bacteria that contained the NAH plasmid encoding genes for the degradation of naphthalene and salicylate, and then subjected to a step input of salicylate solution. Oxygen availability, cell growth, and microbial lag were each examined to determine their effect on the characteristic shape of the salicylate breakthrough curve. For all cases examined, the transport behavior of salicylate was nonsteady. While sparging the influent solution with oxygen increased the total amount of salicylate that was degraded in the column, it did not influence the shape of its initial breakthrough behavior. The effect of microbial lag on the shape of the salicylate breakthrough curve was eliminated in a second substrate pulse by exposing the column to two successive pulses of salicylate, thereby allowing the organisms to acclimate to the carbon source during the first pulse. The cause of the lag was further investigated using succinate, a TCA intermediate that was expected to have minimal metabolic lag. Thus, any lag effects would most likely be related to physiological lag. A very slight lag was observed in the succinate breakthrough curve, indicating that physiological lag was minimal in these systems. This implies that metabolic lag is the primary behavior observed in the characteristic nonsteady transport behavior of salicylate. Elimination of microbial lag effects allowed the impact of bacterial growth on salicylate breakthrough to be quantified.