In wastewater treatment plants, the performance of the biological denitrification processes depend on the key functionally relevant microbial populations, which are affected by many factors, including influent characteristics (e.g., carbon sources), operational conditions, and temperature. This study used Automated Ribosomal Intergenic Spacer Analysis (ARISA) to analyze microbial population structures and dynamics associated with various carbon sourcespecific denitrifying enrichment cultures and reveal the dynamics and microbial diversity, as well as biochemical fundamentals underlying the different denitrification behavior observed. The ability of the specific carbon-acclimated populations to use other alternative carbon sources and the associated changes in microbial community structure was assessed by evaluating the maximum denitrification rates and with ARISA analysis. Although the ARISA profiles showed distinct community structures for denitrifying cultures as a result of enrichment with different carbon sources, no stable community structure or strong correlation between the microbial community signatures with certain carbon sources emerged. Furthermore, the ability of carbonspecific acclimated sludge to utilize other carbon sources varied for different enrichments, showing different acclimatization time duration and denitrification rates .