Potential of cadmium resistant Burkholderia contaminans strain ZCC in promoting growth of soy beans in the presence of cadmium.

Bioremediation of Cd contaminated environments can be assisted by plant-growth-promoting bacteria (PGPB) enabling plant growth in these sites. Here a gram-negative Burkholderia contaminans ZCC was isolated from mining soil at a copper-gold mine. When exposed to Cd(II), ZCC displayed high Cd resistance and the minimal inhibitory concentration was 7 mM in LB medium. Complete genome analysis uncovered B. contaminans ZCC contained 3 chromosomes and 2 plasmids. One of these plasmids was shown to contain a multitude of heavy metal resistance determinants including genes encoding a putative Cd-translocating PIB-type ATPase and an RND-type related to the Czc-system. These additional heavy metal resistance determinants are likely responsible for the increased resistance to Cd(II) and other heavy metals in comparison to other strains of B. contaminans. B. contaminans ZCC also displayed PGPB traits such as 1-aminocyclopropane-1-carboxylate deaminase activity, siderophore production, organic and inorganic phosphate solubilization and indole acetic acid production. Moreover, the properties and Cd(II) binding characteristics of extracellular polymeric substances was investigated. ZCC was able to induce extracellular polymeric substances production in response to Cd and was shown to be chemically coordinated to Cd(II). It could promote the growth of soybean in the presence of elevated concentrations of Cd(II). This work will help to better understand processes important in bioremediation of Cd-contaminated environment.

Electrochemiluminescence for the identification of electrochemically active bacteria.

Electrochemically active bacteria (EAB) use extracellular electron transfer (EET) to exchange electron with extracellular acceptors. Previous studies regarding the measurement of EAB were based on either extracellular reduction or oxidation. In this work, we developed a simple electrochemiluminescence (ECL) assay for the identification and detection of EAB. The results of this proposed method revealed that EET of EAB influenced the content of dissolved oxygen and the formation of Ru(bpy)32+• thus leading to qualitative changes of the ECL signal. EAB with the ability of extracellular reduction (such as Shewanella oneidensis MR-1) gave enhanced signal on ECL emission while those displaying the ability of extracellular oxidation (i.e., Sulfobacillus acidophilus) showed the opposite effect on ECL emission, but non-EAB (i.e., Escherichia coli) did not. These changes in ECL intensity were also proportional to the cell density that could be quantitatively detected in the concentration range of (1.1 ±â€¯1) × 105-212 ±â€¯2 CFU/mL (i.e. Shewanella oneidensis MR-1). Moreover, the measurement of the ability of EAB using this approach was in agreement with measurements using the dissimilatory Fe(III) reduction method. Compared to previous reports, this method displayed a continual and steady ECL signal that allowed accurate measurements of EAB. Most important, only a low cell density was needed in this Ru(bpy)32+ - based ECL method, which is beneficial for cell detection.

Extracellular electron transfer of Enterobacter cloacae SgZ-5T via bi-mediators for the biorecovery of palladium as nanorods.

In nature, microbes use extracellular electron transfer (EET) to recover noble metals. Most attention has been paid to the biorecovery process occurring intracellularly and on the cell surface. In this work, we report that Pd nanorods could be biosynthesized by Enterobacter cloacae SgZ-5T in the extracellular space. This bacterium possesses both a direct EET pathway through membrane redox systems and an indirect EET pathway via the self-secreted electron carrier hydroquinone (HQ). When exposed to Pd(II), the bacteria adjusted their metabolic pathway and membrane-bound proteins to secrete riboflavin (RF). However, no HQ was detected in the supernatant in presence of Pd(II). No significant change was observed through metabolomic analysis regarding the abundance of HQ in presence of Pd(II) compared to Pd(II)-free supernatant. Similar results were also obtained through transcriptomic analysis of YqjG gene encoding glutathionyl-HQ reductase synthase. X-ray photoelectron spectroscopic evidence indicated that HQ may adsorb to the surface of Pd nanorods. Moreover, the gene encoding RF synthase (ribE) was up-regulated in the present of Pd(II), suggesting that this bioreduction process induced RF synthase, which had been shown in previous results. The UV-vis spectroscopy data demonstrated that the Pd(II) reduction rate was enhanced by 5%, 5.5% and 30% by the addition of 3.33 µM HQ, 3.33 µM RF and the both, respectively. All these results revealed that the bi-mediators secreted by bacteria were beneficial for biorecovery of Pd. This work is of significance for understanding metal biorecovery processes and natural biogeochemical processes.