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Modifications in the composition of the SBR bacterial community due to alterations in theoperating conditions were assessed through DGGE profiling of samples collected at the end of thedump feed and fed-batch periods, and after the batch tests carried out in the SBR with DCA feed(Figure 2). The results showed that the changes in performance resulting from the change of theoperational mode were accompanied by shifts in the microbial population present in the SBR. Thefed-batch feeding strategy induced the growth of e.g. organisms related to the rhizospheremicrobiota (uncultured Rhizobium sp. (band K), or Mesorhizobium sp. (band L), both members ofthe Alphaproteobacteria), which is not surprising given their ability to encode aryl acylamidases,one of the key enzymes needed to degrade propanil (Hoagland et al., 1994). Additionally anorganism related to Variovorax sp. (band I) became particularly intense after the DCA feedings,suggesting its association with the degradation of this compound. Earlier studies reported theisolation of two different strains of Variovorax sp. which were able to mineralize phenylureaherbicides as the sole carbon, nitrogen and energy source (Dejonghe et al., 2003; Sørensen etal.2008). Isolates obtained from the acclimatised population included members of the generaEnterococcus and Rhodococcus, as well as Brevundimonas, which displayed >90 % biodegradationefficiency of propanil without accumulation of DCA. Two other isolates (a Stenotrophomonas andan uncultured Betaproteobacteria) displayed good DCA removal, although lower propanildegradation efficiency. None of the isolates corresponded to the DGGE bands observed for the SBRcultures, suggesting that other non-cultivable organisms may be involved in the high degradationperformance observed after acclimatisation.EPL1EPL2EPL5DFDF1FBFB1FB-DCAFB-DCA1EPL3EPL7EPL6EPL4ABCDEFGACIEJFKLAMCIJKLHHHFigure 2. DGGE band pattern of the SRB biomass at different operating conditions (DF - dumpfeed, FB - fed-batch and FB-DCA - fed-batch with DCA as sole C source) and of each of theisolates. Duplicates of each of the mixed culture samples are presented. Sequenced bands areindicated by letters. Excerpt from Carvalho et al. (2010).____________________________________________________________________________________________________________8IWA <strong>Specialist</strong> <strong>Group</strong> on Microbial Ecology and Water Engineering:Newsletter July 2011
Overall, this work defined an effective reactor operation strategy based on fed-batch feeding toobtain a propanil- and DCA-degrading mixed culture, which can be used for bioaugmentation orbioremediation purposes. The culture stability and performance when applied to real contaminatedwater, wastewater and soils is an important issue which deserves future research.AcknowledgementsThe Fundação para a Ciência e Tecnologia (FCT, Portugal) is acknowledged for projectsPTDC/AMB/59836/2004 and PTDC/AMB/65702/2006. We thank Ana Rita Lopes, Cátia Faria,João Paulo Noronha and Olga Nunes for their support and contribution in this work.ReferencesCarvalho, G., Marques, R., Lopes, A.R., Faria, C., Noronha, J.P., Oehmen, A., Nunes, O.C., Reis,M.A.M. (2010). Biological treatment of propanil and 3,4-dichloroaniline: kinetic andmicrobiological characterization. Water Research 44, 4980–4991.Dejonghe, W., Berteloot, E., Goris, J., Boon, N., Crul, K., Maertens, S., Höfte, M., De Vos, P.,Verstraete, W., Top, E.M. (2003). Synergistic degradation of linuron by a bacterial consortiumand isolation of a single linuron-degrading Variovorax strain. Applied and EnvironmentalMicrobiology 69 (3), 1532–1541.Hoagland R.E., Zablotowicz R.M., Locke, M.A. (1994). Propanil metabolism by rhizospheremicroflora. In Bioremediation through Rhizosphere Technology (ed. T.A. Anderson, J.R. Coats),vol. 563, Chapter 14, pp. 160–183. ACS Symposium Series. American Chemical Society.Pothuluri, J.V., Hinson, J.A., Cerniglia, C.E. (1991). Propanil: toxicological characteristics,metabolism, and biodegradation potential in soil. Journal of Environmental Quality 20, 330–347.Primel, E.G., Zanella, R., Kruz, M.H.S., Gonçalves, F.F., Martins, M.L., Machado, S.L.O.,Marchesan, E. (2007). Risk assessment of surface water contamination by herbicide residues:Monitoring of propanil degradation in irrigated rice field waters using HPLC-UV andconfirmation by GC-MS. Journal of the Brazilian Chemical Society 18 (3), 585–589.Sørensen, S.R., Albers, C.N., Aamand, J. (2008). Rapid mineralization of the phenylurea herbicidediuron by Variovorax sp. strain SRS16 in pure culture and within a two-member consortium.Applied and Environmental Microbiology 74 (8), 2332–2340.________________________________________________________________________________________________________IWA <strong>Specialist</strong> <strong>Group</strong> on Microbial Ecology and Water Engineering:9Newsletter July 2011
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