Coping with Polychlorinated Biphenyl (PCB) Toxicity: Physiological and Genome-Wide Responses of
            <i>Burkholderia xenovorans</i>
            LB400 to PCB-Mediated Stress

The genus Burkholderia includes over 60 species isolated from a wide range of environmental niches and can be tentatively divided into two major species clusters. The first cluster includes pathogens such as Burkholderia glumae, B. pseudomallei, and B. mallei and 17 well-studied species of the Burkholderia cepacia complex. The other recently established cluster comprises at least 29 nonpathogenic species, which in most cases have been found to be associated with plants. It was previously established that Burkholderia kururiensis, a member of the latter cluster, possesses an N-acyl homoserine lactone (AHL) quorum-sensing (QS) system designated "BraI/R," which is found in all species of the plant-associated cluster. In the present study, two other BraI/R-like systems were characterized in B. xenovorans and B. unamae and were designated the BraI/R XEN and BraI/R UNA systems, respectively. Several phenotypes were analyzed, and it was determined that exopolysaccharide was positively regulated by the BraIR-like system in the species B. kururiensis, B. unamae, and B. xenovorans, highlighting commonality in targets. However, the three BraIR-like systems also revealed differences in targets since biofilm formation and plant colonization were differentially regulated. In addition, a second AHL QS system designated XenI2/R2 and an unpaired LuxR solo protein designated BxeR solo were also identified and characterized in B. xenovorans LB400 T . The two AHL QS systems of B. xenovorans are not transcriptionally regulating each other, whereas BxeR solo negatively regulated xenI2. The XenI2/R2 and BxeR solo proteins are not widespread in the Burkholderia species cluster. In conclusion, the present study represents an extensive analysis of AHL QS in the Burkholderia plant-associated cluster demonstrating both commonalities and differences, probably reflecting environmental adaptations of the various species.From its establishment in 1992, the genus Burkholderia has been extensively studied since its members are catabolically versatile and are found in many different environments and some are of medical importance (87). Validly described species have been isolated from a wide range of niches, including soil, water, wastes, plants, fungi, animals, and humans. Importantly, several species have been reported to have either a beneficial or a pathogenic interaction with plants, animals, or humans (62, 81). Currently available Burkholderia genome sequences suggest that this genus owes its niche versatility to its large genomes comprised of several large replicons, as well as to lateral gene transfer events and plasmid acquisition (13,44).Taxonomic analysis of more than 60 species described to date shows an internal division of the genus that can be viewed in two major clusters (11, 49). The first cluster includes pathogens such as Burkholderia glumae, B. pseudomallei, and B. mallei, as well as the 17 well-studied species of the Burkholderia cepacia complex (BCC) (83). The second and more recently established cluster comprises more than ...

Section: Discussionmentioning

confidence: 99%

Commonalities and Differences in Regulation of N -Acyl Homoserine Lactone Quorum Sensing in the Beneficial Plant-Associated Burkholderia Species Cluster

Suárez-Moreno¹,

Devescovi²,

Myers

et al. 2010

“…All of those experiments used high PCB concentrations, 20 to 500 g/ml, that were known to be dechlorinated in sediment microcosms or in sediment-free mixed cultures derived from PCB-contaminated sites. PCBs, like other hydrophobic compounds, can adsorb to and partition into cell membranes causing cell stress as manifested in changes in membrane fluidity, decreased cell surface area, and separation of membrane layers (16,25,30). At high PCB-to-cell ratios these effects would presumably be maximal and might be toxic.…”

Section: Discussionmentioning

confidence: 99%

“ Dehalococcoides ” sp. Strain CBDB1 Extensively Dechlorinates the Commercial Polychlorinated Biphenyl Mixture Aroclor 1260

Adrian

Dudková

Демнерова

et al. 2009

129

101

"Dehalococcoides" sp. strain CBDB1 in pure culture dechlorinates a wide range of PCB congeners with three to eight chlorine substituents. Congener-specific high-resolution gas chromatography revealed that CBDB1 extensively dechlorinated both Aroclor 1248 and Aroclor 1260 after four months of incubation. For example, 16 congeners comprising 67.3% of the total PCBs in Aroclor 1260 were decreased by 64%. We confirmed the dechlorination of 43 different PCB congeners. The most prominent dechlorination products were 2,3,5-chlorinated biphenyl (25-3-CB) and 24-3-CB from Aroclor 1248 and 235-25-CB, 25-25-CB, 24-25-CB, and 235-236-CB from Aroclor 1260. Strain CBDB1 removed flanked para chlorines from 3,4-, 2,4,5-, and 3,4,5-chlorophenyl rings, primarily para chlorines from 2,3,4,5-chlorophenyl rings, primarily meta chlorines from 2,3,4-and 2,3,4,6-chlorophenyl rings, and either meta or para chlorines from 2,3,4,5,6-chlorophenyl rings. The site of attack on the 2,3,4-chorophenyl ring was heavily influenced by the chlorine configuration on the opposite ring. This dechlorination pattern matches PCB Process H dechlorination, which was previously observed in situ both in the Acushnet Estuary (New Bedford, MA) and in parts of the Hudson River (New York). Accordingly, we propose that Dehalococcoides bacteria similar to CBDB1 are potential agents of Process H PCB dechlorination in the environment. This is the first time that a complex naturally occurring PCB dechlorination pattern has been reproduced in the laboratory using a single bacterial strain.

“…Rapid dioxygenation of a given CB must not necessarily result in an evolutionary advantage. Indeed, it may result in a disadvantage, if accumulating catabolites exert toxic effects (8,11,12,16,27,29). Moreover, the evolution of catalytic activity in the presence of substrate mixtures will necessarily lead to compromises, so that any given enzyme will only be able to efficiently transform a fraction of substrates.…”

Section: Resultsmentioning

confidence: 99%

Characterization of Biphenyl Dioxygenase Sequences and Activities Encoded by the Metagenomes of Highly Polychlorobiphenyl-Contaminated Soils

Standfuss-Gabisch

Al-Halbouni

Höfer

2012

ABSTRACTTotal extracted DNA from two heavily polychlorobiphenyl-contaminated soils was analyzed with respect to biphenyl dioxygenase sequences and activities. This was done by PCR amplification and cloning of a DNA segment encoding the active site of the enzyme. The translated sequences obtained fell into three similarity clusters (I to III). Sequence identities were high within but moderate or low between the clusters. Members of clusters I and II showed high sequence similarities with well-known biphenyl dioxygenases. Cluster III showed low (43%) sequence identity with a biphenyl dioxygenase fromRhodococcus jostiiRHA1. Amplicons from the three clusters were used to reconstitute and express complete biphenyl dioxygenase operons. In most cases, the resulting hybrid dioxygenases were detected in cell extracts of the recombinant hosts. At least 83% of these enzymes were catalytically active. Several amino acid exchanges were identified that critically affected activity. Chlorobiphenyl turnover by the enzymes containing the prototype sequences of clusters I and II was characterized with 10 congeners that were major, minor, or not constituents of the contaminated soils. No direct correlations were observed between on-site concentrations and rates of productive dioxygenations of these chlorobiphenyls. The prototype enzymes displayed markedly different substrate and product ranges. The cluster II dioxygenase possessed a broader substrate spectrum toward the assayed congeners, whereas the cluster I enzyme was superior in the attack ofortho-chlorinated aromatic rings. These results demonstrate the feasibility of the applied approach to functionally characterize dioxygenase activities of soil metagenomes via amplification of incomplete genes.