The microbial community associated with a bioremediation system comprised of a fluidized bed reactor to clean dieselcontaminated groundwater in Vega Baja, Puerto Rico was examined with the GeoChip 1.0 (Rodríguez-Martínez et al., 2006) . Genes involved in the degradation of diesel fuel and other organic contaminants (acetylene, aniline, benzoate, biphenyl, cyclohexanol, methyl tert-butyl ether, naphthalene, phthalate, protocatechuate, and toluene) were detected. Increased signal intensities for genes involved in anaerobic benzoate degradation indicated a shift toward anaerobiosis over time, a conclusion supported by other experimental evidence. Liang et al. (2009b) examined the effect of different bioremediation treatments on microbial communities using laboratory scale bioremediation systems with sediment from contaminated oil fields and inoculated with oil degrading enrichment cultures. The systems were incubated 242 days, treated with ozone, and incubated an additional 125 days. Many oil degradation genes (benzene, benzoate, catechol, polyaromatic hydrocarbon aromatics, protocatechuate, phthalate) were detected with GeoChip 2.0. Ozonation treatment resulted in an almost 50% reduction in the number of functional genes detected. Gene numbers increased again after a recovery period and the community retained the ability to degrade oil.