Bacterial aggregation has important implications for the maintenance of bacteria in engineered environments. The triggers for aggregation, however, are poorly understood. A strain of Acidovorax temperans CB2Hn isolated from activated sludge was found to exhibit transient aggregation and was applied as a model to investigate factors that regulate biological aggregation. Growth kinetic studies indicate CB2Hn has exponential growth rates (mu (max)) ranging from 0.11 to 0.75 (log(CFU mL(-1))h(-1)) depending on nutrient conditions. CB2Hn exhibited variable aggregation in growth media that differed in the type of available carbon. Aggregation indices and extracellular polysaccharide polymer levels showed transient maxima which occurred at different points in the growth curve for each medium type. Maximum aggregation points were detected at the beginning of log phase in media containing complex carbon sources. In contrast, maximum values were detected in early log phase and mid-to-late log phase in media containing both simple and complex carbon sources. The results suggest that aggregation is regulated by nutritional cues and is possibly triggered by the switch to utilisation of complex carbon substrates.