Obogaćivanje i karakterizacija bakterija aktivnih u razgradnji polikloriranih bifenila kao potencijalnih starter kultura za biološki oporavak onečišćenih tala

Abstract

The main objective of our study was to obtain seed cultures for enhancing the transformation of polychlorinated biphenyls (PCBs) in contaminated soil of the transformer station in Zadar, Croatia, damaged during warfare activities in 1991. For enrichment, six soil samples were collected from different polluted areas and microcosm approach, stimulating the growth of biphenyl-degrading bacteria, was employed. Enrichment experiments resulted in the selection of two fast growing mixed cultures TSZ7 and AIR1, originating from the soil of the transformer station and the airport area, respectively. Both cultures showed significant PCB-degrading activity (56 to 60 % of PCB50 mixture was reduced after a two-week cultivation). Furthermore, the cultures displayed similar PCB-degrading competence and reduced di-to tetrachlorobiphenyls more effectively than penta- to hepta-chlorobiphenyls. Strain Z6, identified as Rhodococcus erythropolis, was found to be the only culture member showing PCB-transformation potential similar to that of the mixed culture TSZ7, from which it was isolated. Based on the metabolites identified in the assay with the single congener 2,4,4’-chlorobiphenyl, we proposed that the strain Z6 was able to use both the 2,3-and 3,4-dioxygenase pathways. Furthermore, the identified metabolites suggested that beside these pathways another unidentified pathway might also be active in strain Z6. Based on the obtained results, the culture TSZ7 and the strain Z6 were designated as potential seed cultures for bioremediation of the contaminated soil.Osnovni je cilj istraživanja bio dobivanje katabolički aktivnih kultura za ubrzanje razgradnje polikloriranih bifenila (polychlorinated biphenyls – PCBs) u onečišćenom tlu u blizini zadarske trafostanice (Hrvatska) koja je oštećena tijekom domovinskoga rata godine 1991. Obogaćivanje aktivnih bakterija provedeno je iz 6 uzoraka tala sakupljenih s različitih područja onečišćenih polikloriranim bifenilima te je primijenjena metoda submerznog uzgoja uz poticanje rasta bakterija koje mogu razgrađivati bifenil. Tim su postupkom izdvojene dvije mješovite kulture (TSZ7 i AIR1, potječu iz tla u blizini trafostanice i zračne luke), koje su najbolje rasle na bifenilu. Obje su kulture pokazale podjednaku sposobnost razgradnje bifenila (nakon dva tjedna uzgoja razgrađeno je 56-60 % smjese PCB50) te su brže razgrađivale di-, tri- i tetraklorbifenile nego penta-, heksa- i heptaklorbifenile. Soj Z6, Rhodococus erythropolis, bio je jedini član mješovite kulture TSZ7 koji je pokazao sposobnost razgradnje polikloriranih bifenila. Na osnovi metabolita identificiranih u pokusu s pojedinačnim kongenerom (2,4,4\u27-klorbifenilom) i sojem Z6 pretpostavlja se da su u razgradnji tog spoja uključena oba enzima, 2,3- i 3,4-dioksigenaza. Također se pretpostavlja da soj Z6 može aktivirati i neki drugi, neidentificirani metabolički put u razgradnji polikloriranih bifenila. Temeljem postignutih rezultata mješovita kultura TSZ7 i soj Z6 odabrani su kao starter kulture za biološki oporavak onečišćenih tala