Burkholderia sp. DBT1 is a bacterial strain formerly isolated from the wastewater dicharge pipeline of an oil refinery located in Tuscany, Italy. It is cable of biodegrading dibenzothiophene (DBT) in liquid culture through the “Kodama pathway” within three days of incubation. Molecular characterization of the strain DBT1 has shown the presence of an unusual genetic structure. Actually, the genes involved in dibenzothiophene transformation are harbored in two operons (namely, p51 and pH1A) and show low similarity to both nah-like and phn-like genes. Since DBT results to be a recalcitrant compound and tends to bioaccumulate throughout the food chain, isolation and characterization of bacterial strains able to use it as sole source of carbon and energy is of great interest for bioremediation purposes. Nevertheless for a safe exploitation of Burkholderia sp. DBT1 in bioremediation protocols, the exclusion of such strain from the Burkholderia cepacia complex (BCC) is of prominent importance. Actually, members of this complex are responsible for opportunistic human infections. Thus, the objective of the present study was to investigate the taxonomic position of DBT1 within the genus Burkholderia, in order to demonstrate no affiliation of this strain to BCC. Both classical (API 20E, API 20 NE, fatty acid composition, carbon source utilization) and molecular (PCR protocols, DNA sequencing, DNA-DNA hybridization) analyses were carried out. Burkholderia DBT1 has been compared with strains belonging to its phylogenetic surrounding, (namely, B. fungorum, B. graminis, B. cepacia and B. caledonica). All results obtained indicate a strong relationship of DBT1 with B. fungorum. In particular, the sequencing of both 16S hypervariable regions (V3 and V6-V8) and housekeeping protein-coding genes (i.e. RecA and GyrB) evidenced such a high similarity with B. fungorum as well as a great divergence from B. cepacia strains. Moreover, the PCR reaction aimed to detect in DBT1 the presence of esmR, a molecular markers encoding for “B. cepacia epidemic strain marker” (BCESM), gave a negative result. Finally, the DNA-DNA hybridization analysis definitively revealed the affiliation of DBT1 strain to Burkholderia fungorum species, with a percentage of hybridization of 78,2 ± 2,9%.
Burkholderia sp. DBT1 a promising bacterial strain for bioremediation protocols non-related to the Burkholderia cepacia complex (BCC)
ANDREOLLI, Marco;LAMPIS, Silvia;VALLINI, Giovanni
2009-01-01
Abstract
Burkholderia sp. DBT1 is a bacterial strain formerly isolated from the wastewater dicharge pipeline of an oil refinery located in Tuscany, Italy. It is cable of biodegrading dibenzothiophene (DBT) in liquid culture through the “Kodama pathway” within three days of incubation. Molecular characterization of the strain DBT1 has shown the presence of an unusual genetic structure. Actually, the genes involved in dibenzothiophene transformation are harbored in two operons (namely, p51 and pH1A) and show low similarity to both nah-like and phn-like genes. Since DBT results to be a recalcitrant compound and tends to bioaccumulate throughout the food chain, isolation and characterization of bacterial strains able to use it as sole source of carbon and energy is of great interest for bioremediation purposes. Nevertheless for a safe exploitation of Burkholderia sp. DBT1 in bioremediation protocols, the exclusion of such strain from the Burkholderia cepacia complex (BCC) is of prominent importance. Actually, members of this complex are responsible for opportunistic human infections. Thus, the objective of the present study was to investigate the taxonomic position of DBT1 within the genus Burkholderia, in order to demonstrate no affiliation of this strain to BCC. Both classical (API 20E, API 20 NE, fatty acid composition, carbon source utilization) and molecular (PCR protocols, DNA sequencing, DNA-DNA hybridization) analyses were carried out. Burkholderia DBT1 has been compared with strains belonging to its phylogenetic surrounding, (namely, B. fungorum, B. graminis, B. cepacia and B. caledonica). All results obtained indicate a strong relationship of DBT1 with B. fungorum. In particular, the sequencing of both 16S hypervariable regions (V3 and V6-V8) and housekeeping protein-coding genes (i.e. RecA and GyrB) evidenced such a high similarity with B. fungorum as well as a great divergence from B. cepacia strains. Moreover, the PCR reaction aimed to detect in DBT1 the presence of esmR, a molecular markers encoding for “B. cepacia epidemic strain marker” (BCESM), gave a negative result. Finally, the DNA-DNA hybridization analysis definitively revealed the affiliation of DBT1 strain to Burkholderia fungorum species, with a percentage of hybridization of 78,2 ± 2,9%.
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