Transport of haloacids across biological membranes.

Haloacids are considered to be environmental pollutants, but some of them have also been tested in clinical research. The way that haloacids are transported across biological membranes is important for both biodegradation and drug delivery purposes. In this review, we will first summarize putative haloacids transporters and the information about haloacids transport when studying carboxylates transporters. We will then introduce MCT1 and SLC5A8, which are respective transporter for antitumor agent 3-bromopyruvic acid and dichloroacetic acid, and monochloroacetic acid transporters Deh4p and Dehp2 from a haloacids-degrading bacterium. Phylogenetic analysis of these haloacids transporters and other monocarboxylate transporters reveals their evolutionary relationships. Haloacids transporters are not studied to the extent that they deserve compared with their great application potentials, thus future inter-discipline research are desired to better characterize their transport mechanisms for potential applications in both environmental and clinical fields.

Complete Genome Sequence of the Exopolysaccharide-Producing Burkholderia caribensis Type Strain MWAP64.

We report the complete genome sequence of Burkholderia caribensis MWAP64 (LMG 18531), which was isolated from soil for its proficiency in producing large amounts of exopolysaccharide that help form microaggregates in a vertisol. There are four replicons with a total size of 9,032,119 bp.

Complete genome sequence and characterization of the haloacid-degrading Burkholderia caribensis MBA4.

Burkholderia caribensis MBA4 was isolated from soil for its capability to grow on haloacids. This bacterium has a genome size of 9,482,704 bp. Here we report the genome sequences and annotation, together with characteristics of the genome. The complete genome sequence consists of three replicons, comprising 9056 protein-coding genes and 80 RNA genes. Genes responsible for dehalogenation and uptake of haloacids were arranged as an operon. While dehalogenation of haloacetate would produce glycolate, three glycolate operons were identified. Two of these operons contain an upstream glcC regulator gene. It is likely that the expression of one of these operons is responsive to haloacetate. Genes responsible for the metabolism of dehalogenation product of halopropionate were also identified.

Draft Genome Sequence of the Haloacid-Degrading Burkholderia caribensis Strain MBA4.

Burkholderia caribensis MBA4 was isolated from soil for its ability to utilize 2-haloacid. An inducible haloacid operon, encoding a dehalogenase and a permease, is mainly responsible for the biotransformation. Here, we report the draft genome sequence of this strain.

Enhanced degradation of haloacid by heterologous expression in related Burkholderia species.

Haloacids are environmental pollutant and can be transformed to non-toxic alkanoic acids by microbial dehalogenase. Bacterium Burkholderia species MBA4 was enriched from soil for its ability to bioremediate haloacids such as mono-chloroacetate (MCA), mono-bromoacetate (MBA), 2-mono-chloropropionate, and 2-mono-bromopropionate. MBA4 produces an inducible dehalogenase Deh4a that catalyzes the dehalogenation process. The growth of MBA4 on haloacid also relies on the presence of a haloacid-uptake system. Similar dehalogenase genes can be found in the genome of many related species. However, wildtype Burkholderia caribensis MWAP64, Burkholderia phymatum STM815, and Burkholderia xenovorans LB400 were not able to grow on MCA. When a plasmid containing the regulatory and structural gene of Deh4a was transformed to these species, they were able to grow on haloacid. The specific enzyme activities in these recombinants ranges from 2- to 30-fold that of MBA4 in similar condition. Reverse transcription-quantitative real-time PCR showed that the relative transcript levels in these recombinant strains ranges from 9 to over 1,600 times that of MBA4 in similar condition. A recombinant has produced nearly five times of dehalogenase that MBA4 could ever achieve. While the expressions of Deh4a were more relaxed in these phylogenetically related species, an MCA-uptake activity was found to be inducible. These metabolically engineered strains are better degraders than the haloacid-enriched MBA4.

Transports of acetate and haloacetate in Burkholderia species MBA4 are operated by distinct systems.

BACKGROUND: Acetate is a commonly used substrate for biosynthesis while monochloroacetate is a structurally similar compound but toxic and inhibits cell metabolism by blocking the citric acid cycle. In Burkholderia species MBA4 haloacetate was utilized as a carbon and energy source for growth. The degradation of haloacid was mediated by the production of an inducible dehalogenase. Recent studies have identified the presence of a concomitantly induced haloacetate-uptake activity in MBA4. This uptake activity has also been found to transport acetate. Since acetate transporters are commonly found in bacteria it is likely that haloacetate was transported by such a system in MBA4. RESULTS: The haloacetate-uptake activity of MBA4 was found to be induced by monochloroacetate (MCA) and monobromoacetate (MBA). While the acetate-uptake activity was also induced by MCA and MBA, other alkanoates: acetate, propionate and 2-monochloropropionate (2MCPA) were also inducers. Competing solute analysis showed that acetate and propionate interrupted the acetate- and MCA- induced acetate-uptake activities. While MCA, MBA, 2MCPA, and butyrate have no effect on acetate uptake they could significantly quenched the MCA-induced MCA-uptake activity. Transmembrane electrochemical potential was shown to be a driving force for both acetate- and MCA- transport systems. CONCLUSIONS: Here we showed that acetate- and MCA- uptake in Burkholderia species MBA4 are two transport systems that have different induction patterns and substrate specificities. It is envisaged that the shapes and the three dimensional structures of the solutes determine their recognition or exclusion by the two transport systems.