Protein Model and Function Analysis in Quorum-Sensing Pathway of Vibrio qinghaiensis sp.-Q67

Bioluminescent bacteria are mainly found in marine habitats. Vibrio qinghaiensis sp.-Q67 (Q67), a nonpathogenic freshwater bacterium, has been a focus due to its wide use in the monitoring of environmental pollution and the assessment of toxicity. However, the lack of available crystal structures limits the elucidation of the structures of the functional proteins of the quorum-sensing (QS) system that regulates bacterial luminescence in Q67. In this study, 19 functional proteins were built through monomer and oligomer modeling based on their coding proteins in the QS system of Q67 using MODELLER. Except for the failure to construct LuxM due to the lack of a suitable template, 18 functional proteins were successfully constructed. Furthermore, the relationships between the function and predicted structures of 19 functional proteins were explored one by one according to the three functional classifications: autoinducer synthases and receptors, signal transmission proteins (phosphotransferases, an RNA chaperone, and a transcriptional regulator), and enzymes involved in bacterial bioluminescence reactions. This is the first analysis of the whole process of bioluminescence regulation from the perspective of nonpathogenic freshwater bacteria at the molecular level. It provides a theoretical basis for the explanation of applications of Q67 in which luminescent inhibition is used as the endpoint.

Generation of Fluorescent Bacteria with the Genes Coding for Lumazine Protein and Riboflavin Biosynthesis

Lumazine protein is a member of the riboflavin synthase superfamily and the intense fluorescence is caused by non-covalently bound to 6,7-dimethyl 8-ribityllumazine. The pRFN4 plasmid, which contains the riboflavin synthesis genes from Bacillus subtilis, was originally designed for overproduction of the fluorescent ligand of 6,7-dimethyl 8-ribityllumazine. To provide the basis for a biosensor based on the lux gene from bioluminescent bacteria of Photobacterium leiognathi, the gene coding for N-terminal domain half of the lumazine protein extending to amino acid 112 (N-LumP) and the gene for whole lumazine protein (W-LumP) from P. leiognathi were introduced by polymerase chain reaction (PCR) and ligated into pRFN4 vector, to construct the recombinant plasmids of N-lumP-pRFN4 and W-lumP-pRFN4 as well as their modified plasmids by insertion of the lux promoter. The expression of the genes in the recombinant plasmids was checked in various Escherichia coli strains, and the fluorescence intensity in Escherichia coli 43R can even be observed in a single cell. These results concerning the co-expression of the genes coding for lumazine protein and for riboflavin synthesis raise the possibility to generate fluorescent bacteria which can be used in the field of bio-imaging.

Direct and Indirect Detoxification Effects of Humic Substances

The review summarizes studies on the detoxification effects of water-soluble humic substances (HS), which are products of the natural transformation of organic substances in soils and bottom sediments that serve as natural detoxifying agents in water solutions. The detoxifying effects of HS on microorganisms are quite complex: HS neutralize free pollutants (indirect bioeffects) and also stimulate the protective response of organisms (direct bioeffects). Prospects and potential problems of bioluminescent bacteria-based assay to monitor toxicity of solutions in the presence of HS are discussed. The main criterion for the bioassay application is versatility and ease of use. The detoxification efficiency of HS in different pollutant solutions was evaluated, and the detoxification mechanisms are discussed. Particular attention was paid to the direct and complex direct + indirect effects of HS. The review focuses on the protective function of HS in solutions of radionuclides and salts of stable metals, with special consideration of the antioxidant properties of HS.

Imaging the oxygen wave with single bioluminescent bacteria

We developed a capability of a monolayer of bioluminescent (BL) bacteria for spatiotemporally visualizing the heterogeneous distribution and dynamic evolution of interfacial oxygen concentration, resulting in the discovery of spontaneous...