Cyclic Dipeptides Mediating Quorum Sensing and Their Biological Effects in Hypsizygus Marmoreus.

A novel quorum sensing (QS) system was discovered in Serratia odorifera, the symbiotic bacterium of Hypsizygus marmoreus. This system uses cyclo(Pro-Phe), cyclo(Pro-Tyr), cyclo(Pro-Val), cyclo(Pro-Leu), cyclo(Tyr-Leu), and cyclo(Tyr-Ile) as autoinducers. This discovery is the first attempt to characterize cyclic dipeptides as QS signaling molecules in S. odorifera and improves the classical QS theory. Significantly, except for cyclo(Tyr-Leu), these QS autoinducers can increase the transcription level of lignin-degrading enzyme genes of H.marmoreus. The cyclo(Pro-Phe) can increase the activity of extracellular laccase (1.32-fold) and manganese peroxidase (20%), which may explain why QS potentially regulates the hyphal growth, primordium formation, and fruit body development of H. marmoreus. Furthermore, it was demonstrated that the cyclo(Tyr-Ile) biosynthesis in S. odorifera was catalyzed by the nonribosomal peptide synthetase (NRPS). This study supports exploring the growth and development of H.marmoreus promoted by its symbiotic bacteria at QS signal transduction level.

Polyvinyl alcohol degradation by Bacillus cereus RA23 from oil sludge sample.

A novel polyvinyl alcohol (PVA)-degrading strain Bacillus cereus RA23 was isolated from an oil sludge sample and environmental factors affecting its PVA degradation efficiency were optimized in detail. Inorganic nitrogen source, ammonium chloride (NH4Cl), was found to be the best nitrogen source and enhanced the PVA degradation rate greatly. The optimal medium for PVA biodegradation consisted of (g/L) PVA 1, NH4Cl 1, K2HPO4 1.6, MgSO4·7H2O 0.05, FeSO4·6H2O 0.02, CaCl2 0.05, NaCl 0.02. The optimal temperature and pH for PVA biodegradation by strain RA23 was 28 °C and 7.0, respectively, and 85% of 0.1% PVA was degraded after 5 days under these conditions. FTIR studies showed that the carboxylic acids (possibly including aldehyde or ketone) could be the intermediate product of PVA biodegradation. The investigation of strain RA23 for PVA degradation will provide important information to facilitate the removal of wastewater pollution in industrial zones.

Degradation of polyvinyl alcohol by a novel bacterial strain Stenotrophomonas sp. SA21.

In this study, polyvinyl alcohol (PVA)-degrading bacteria were screened from oil sludge using PVA as a sole source of carbon in the culture medium. A novel strain, SA21, was obtained and identified as a member of the Stenotrophomonas genus based on the analysis of a partial 16S rDNA nucleotide sequence, morphological and biochemical characteristics, and phylogenetic analysis. This Stenotrophomonas isolate had not previously been reported as a PVA-degrading bacterium. Stenotrophomonas sp. strain SA21 degraded 90% of the PVA present in the culture medium after 4 days. The effect of nitrogen sources on the production of PVA-degrading enzyme involved in the biodegradation process was significant, and the enzymatic activity reached 82 U/ml when ammonium nitrate or urea was used in the optimized medium. The information obtained in this study will provide a foundation for improving industrial wastewater treatment. ABBREVIATIONS: DCW: dry cell weight; FTIR: Fourier Transform Infrared Spectroscopy; NCBI: National Center for Biotechnology Information; PCR: polymerase chain reaction; PVA: polyvinyl alcohol; SEM: scanning electron microscope.

The response of Serratia marcescens JG to environmental changes by quorum sensing system.

Many bacterial cells are known to regulate their cooperative behaviors and physiological processes through a molecular mechanism called quorum sensing. Quorum sensing in Serratia marcescens JG is mediated by the synthesis of autoinducer 2 (AI-2) which is a furanosyl borate diester. In this study, the response of quorum sensing in S. marcescens JG to environment changes such as the initial pH, carbon sources and boracic acid was investigated by a bioreporter and real-time PCR analysis. The results show that glucose can affect AI-2 synthesis to the greatest extent, and 2.0 % glucose can stimulate S. marcescens JG to produce more AI-2, with a 3.5-fold increase in activity compared with control culture. Furthermore, the response of quorum sensing to changes in glucose concentration was performed by changing the amount of luxS RNA transcripts. A maximum of luxS transcription appeared during the exponential growth phase when the glucose concentration was 20.0 g/L. AI-2 production was also slightly impacted by the low initial pH. It is significant for us that the addition of boracic acid at microdosage (0.1-0.2 g/L) can also induce AI-2 synthesis, which probably demonstrated the feasible fact that the 4,5-dihydroxy-2, 3-pentanedione cyclizes by the addition of borate and the loss of water, is hydrated and is converted to the final AI-2 in S. marcescens JG.