The automated docking program DOCK 5.3.0 was applied to screening for quorum sensing inhibitors (QSIs) of Peudomonus aeruginosa from a database containing 51 active components of Traditional Chinese Medicines with antibacterial activity. Five potential QSIs were revealed by the computer-based virtual screening. The compounds 3, 4, 5, 6, 7 inhibit biofilm formation of P. aeruginosa at a concentration of 200 microM. Compound 4 (baicalein) does not inhibit the growth of P. aeruginosa; however, it significantly inhibits biofilm formation of the bacteria at a lower concentration of 20 microM and promoted proteolysis of the signal receptor TraR protein in Escherichia coli at 4-40 mM. Baicalein and ampicillin showed synergistic activity against P. aeruginosa. These results suggested that baicalein can interfere with quorum sensing system of P. aeruginosa and will be developed as antibacterial agent with novel target.

China remains by far the largest aquaculture producer in the world. However, biofilms formed by pathogenic Vibrio strains pose serious problems to marine aquaculture. To provide a strategy for biofilm prevention, control, and eradication, extracts from 88 marine actinomycetes were screened. Thirty-five inhibited the biofilm formation of Vibrio harveyi, Vibrio vulnificus, and Vibrio anguillarum at a concentration of 2.5% (v/v). Thirty-three of the actinomycete extracts dispersed the mature biofilm. Six extracts inhibited the quorum-sensing system of V. harveyi by attenuating the signal molecules N-acylated homoserine lactones' activity. Strain A66, which was identified as Streptomyces albus, both attenuated the biofilms and inhibited their quorum-sensing system. It is suggested that strain A66 is a promising candidate to be used in future marine aquaculture.

The delta subunit of RNA polymerase, RpoE, is widespread in low-G؉C Gram-positive bacteria and is thought to play a role in enhancing transcriptional specificity by blocking RNA polymerase binding at weak promoter sites and stimulating RNA synthesis by accelerating core enzyme recycling. Despite the well-studied biochemical properties of RpoE, a role for this protein in vivo has not been defined in depth. In this study, we show that inactivation of rpoE in the human dental caries pathogen Streptococcus mutans causes impaired growth and loss of important virulence traits, including biofilm formation, resistance to antibiotics, and tolerance to environmental stresses. Complementation of the mutant with rpoE expressed in trans restored its phenotype to wild type. The luciferase fusion reporter showed that rpoE was highly transcribed throughout growth and that acid and hydrogen peroxide stresses repressed rpoE expression. Transcriptome profiling of wild-type and ⌬rpoE cells in the exponential and early stationary phase of growth, under acid and hydrogen peroxide stress and under both stresses combined, revealed that genes involved in histidine synthesis, malolactic fermentation, biofilm formation, and antibiotic resistance were downregulated in the ⌬rpoE mutant under all conditions. Moreover, the loss of RpoE resulted in dramatic changes in transport and metabolism of carbohydrates and amino acids. Interestingly, differential expression, mostly upregulation, of 330 noncoding regions was found. In conclusion, this study demonstrates that RpoE is an important global modulator of gene expression in S. mutans which is required for optimal growth and environmental adaptation.

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To characterize the alginate lyase produced by rhizosphere Streptomyces, Streptomyces sp. A5 was isolated from banana rhizosphere, and its extracellular lyase was purified to an electrophoretically homogeneous state. The lyase has a molecular mass of 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimum temperature and pH were 37 degrees C and pH 7.5, respectively. Ninety-two percent of the activity was lost after incubation at 70 degrees C and pH 7.5 for 20 min. The enzyme was inhibited by 0.05 M SDS and 2 mM Hg2+, Cu2+, and Fe3+, but EDTA enhanced the enzyme activity. The Km value of the lyase was 0.13 mg mL-1 with the substrate sodium alginate. The lyase had substrate specificity for polyguluronate units in the alginate molecules. The alginate oligomers prepared by the lyase show growth-promoting activity on the roots of banana plantlets. These results indicated that the encapsulation method using alginate microbeads to inoculate beneficial streptomycete strains might be beneficial to the root growth of banana plantlets.