N-Acylhomoserine lactones (AHLs) are used as quorum-sensing signal molecules by many gram-negative bacteria. We have reported that Solibacillus silvestris, which was isolated from the potato leaf, has AHL-degrading activity. To identify the AHL-degrading gene, whole genome sequencing of S. silvestris StLB046 was performed by using pyrosequencing technology. As the result of the BLAST search, one predicted ORF (ahlS) showed slight similarity to AiiA-like AHL lactonase from Bacillus cereus group. Escherichia coli harboring the ahlS-expressing plasmid showed high AHL-degrading activity. The ahlS-cording region was also amplified by PCR from the other potato leaf-associated and AHL-degrading S. silvestris strains. Purified AhlS as a maltose binding fusion protein showed high AHL-degrading activity and catalyzes AHL ring opening by hydrolyzing lactones. In addition, expression of ahlS in plant pathogen Pectobacterium carotovorum subsp. carotovorum attenuated maceration of the potato slices. Our results suggest that AHL-degrading activity of ahlS might perform useful functions such as useful biocontrol agents.
"Strain W01 was selected during the screening of microbial strains that have flocculating ability for harvesting marine microalgae N. oceanica DUT01 by flocculation. The 1482-bp 16S rRNA sequence of W01 shared 99% identity with S. silvestris StLB406 (Morohoshi et al., 2012). Therefore, strain W01 was identified as S. silvestris. "
[Show abstract][Hide abstract] ABSTRACT: Microalgae are widely studied for biofuel production, however, current technologies to harvest microalgae for this purpose are not well developed. In this work, a bacterial strain W01 was isolated from activated sludge and identified as Solibacillus silvestris. Bioflocculant in the culture broth of W01 showed 90% flocculating efficiency on marine microalga Nannochloropsis oceanica, and no metal ion was required for the flocculation process. Chemical analysis of the purified bioflocculant indicated that it is a proteoglycan composed of 75.1% carbohydrate and 24.9% protein (w/w). The bioflocculant exhibits no effect on the growth of microalgal cells and can be reused to for economical harvesting of N. oceanica. This is the first report that strain of S. silvestris can produce bioflocculant for microalgae harvest. The novel bioflocculant produced by W01 has the potential to harvest marine microalgae for cost-effective production of microalgal bioproducts.
[Show abstract][Hide abstract] ABSTRACT: N-Acylhomoserine lactones (AHLs) are used as quorum-sensing (QS) signal molecules by many Gram-negative bacteria. We have reported that Chryseobacterium sp. strain StRB126, which was isolated from the root surface of potato, has AHL-degrading activity. In this study, we cloned and characterized the aidC gene from the genomic library of StRB126. AidC has AHL-degrading activity and shows homology to several metallo-β-lactamase proteins from Bacteroidetes, although not to any known AHL-degrading enzymes. Purified AidC, as a maltose-binding fusion protein, showed high degrading activity against all tested AHLs, whether short- or long-chain forms, with or without substitution at carbon 3. High-performance liquid chromatography (HPLC) analysis revealed that AidC functions as an AHL lactonase catalyzing AHL ring opening by hydrolyzing lactones. An assay to determine the effects of covalent and ionic bonding showed that Zn(2+) is important to AidC activity both in vitro and in vivo. In addition, the aidC gene could also be PCR amplified from several other Chryseobacterium strains. In conclusion, this study indicated that the aidC gene, encoding a novel AHL lactonase, may be widespread throughout the genus Chryseobacterium. Our results extend the diversity and known bacterial hosts of AHL-degrading enzymes.
[Show abstract][Hide abstract] ABSTRACT: In a polymicrobial community, while some bacteria are communicating with neighboring cells (quorum sensing), others are interrupting the communication (quorum quenching), thus creating a constant arms race between intercellular communication. In the past decade, numerous quorum quenching enzymes have been found and initially thought to inactivate the signalling molecules. Though this is widely accepted, the actual roles of these quorum quenching enzymes are now being uncovered. Recent evidence extends the role of quorum quenching to detoxification or metabolism of signalling molecules as food and energy source; this includes "signalling confusion", a term coined in this paper to refer to the phenomenon of non-destructive modification of signalling molecules. While quorum quenching has been explored as a novel anti-infective therapy targeting, quorum sensing evidence begins to show the development of resistance against quorum quenching.
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