Complete characterisation of Tn5530 from Burkholderia cepacia strain 2a (pIJB1) and studies of 2,4-dichlorophenoxyacetate uptake by the organism.

The complete genetic characterisation of Tn5530 in Burkholderia cepacia strain 2a (pIJB1) has been accomplished, indicating that it is a Tn3-like transposon with a complex structure bearing operons for the catabolism of 2,4-dichlorophenoxyacetate (2,4-D) and malonate. Tn5530 is terminated at both ends by the IS1071::IS1471 element and the 2,4-D- and malonate-dissimilatory operons are separated by a region encoding a putA and lrp gene and a gene encoding a chloride channel protein. The chloride channel protein may have a role in the expulsion of chloride ions liberated by the dissimilation of 2,4-D. In addition, a putative transposase with a high level of sequence similarity to those of plasmid pGH1 from Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. glycinea, and a transcription factor similar to those of the TetR family with low but significant levels of sequence similarity to those identified in a number of other organisms was observed. The entire Tn5530 sequence length, including the IS1071::IS1471 elements, was found to be 40,956bp, and pIJB1 was replicon-typed and otherwise characterised as being of the IncP-1beta subgroup, bearing merA and merD genes conferring resistance to mercuric chloride. The rate of uptake of 2,4-D by B. cepacia strain 2a was observed to proceed more readily at acid pH, suggesting involvement of the undissociated form of the compound. Uptake did not show saturation kinetics, was concentration-dependent, and appeared to occur in two stages; an initial accumulation followed by a linear second phase. Uptake could be inhibited by sodium azide but not by arsenate, N,N(')-dicyclohexylcarbodi-imide (DCCD) or carbonylcyanide m-chlorophenyl-hydrazone (CCCP) suggesting that it is not energy-dependent

2,4-Dichlorophenoxyacetate/alpha-ketoglutarate dioxygenases from Burkholderia cepacia 2a and Ralstonia eutropha JMP134

2,4-Dichlorophenoxyacetate (2,4-D)/alpha -ketoglutarate (alpha -KG) dioxygenase has been purified to apparent homogeneity from Burkholderia cepacia strain 2a, which utilizes 2.4-D as sole carbon source. The enzyme required ferrous ions, and was a homodimer composed of subunits having an M-r of similar to 32,000. The reaction catalysed consumed one mol each of 2,4-D, alpha -KG and dioxygen, with the production of one mol each of succinate, 2,4-dichlorophenol and glyoxylate. Maximum activity was exhibited at pH 7.8 and 25 degreesC, and reactivity was enhanced by the presence of ascorbate and cysteine. Mn2+, Zn2+, Cu2+ Fe3+ and Co2+ were inhibitory, and chemical modification of the dioxygenase revealed that thiol groups were essential for activity. The enzyme was active towards other substituted phenoxyacetates, but reacted most rapidly with 2,4-D. The apparent Michaelis constants for 2,4-D and alpha -KG were 109 and 8.9 muM, respectively. The properties of this enzyme are compared with those of the 2,4-D/alpha -KG dioxygenase from Ralstonia eutropha JMP134, which exhibits a differing N-terminal amino-acid sequence, and a different temperature 'optimum', pH optimum, substrate specificity and sensitivity to thiol-binding reagents

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta