Control of the Transcription of a Short Gene Encoding a Cyclic Peptide in Streptococcus thermophilus: a New Quorum-Sensing System?▿

Gram-positive bacteria secrete a variety of peptides that are often subjected to posttranslational modifications and that are either antimicrobials or pheromones involved in bacterial communication. Our objective was to identify peptides secreted by Streptococcus thermophilus, a nonpathogenic bacterium widely used in dairy technology in association with other bacteria, and to understand their potential roles in cell-cell communication. Using reverse-phase liquid chromatography, mass spectrometry, and Edman sequencing, we analyzed the culture supernatants of three S. thermophilus strains (CNRZ1066, LMG18311, and LMD-9) grown in a medium containing no peptides. We identified several peptides in the culture supernatants, some of them found with the three strains while others were specific to the LMD-9 strain. We focused our study on a new modified peptide secreted by S. thermophilus LMD-9 and designated Pep1357C. This peptide contains 9 amino acids and lost 2 Da in a posttranslational modification, most probably a dehydrogenation, leading to a linkage between the Lys2 and Trp6 residues. Production of Pep1357C and transcription of its encoding gene depend on both the medium composition and the growth phase. Furthermore, we demonstrated that transcription of the gene coding for Pep1357C is drastically decreased in mutants inactivated for the synthesis of a short hydrophobic peptide, a transcriptional regulator, or the oligopeptide transport system. Taken together, our results led us to deduce that the transcription of the Pep1357C-encoding gene is controlled by a new quorum-sensing system

An Integrated Study on Analysis, Intelligence and Repair of Composite Structures with Damage(II)

本整合計劃將集合相關研究之教授，以分工合作方式研究受損複材結構(以樑、板為主)在受損(如脫層)後其結構之各種力學行為分析(層間應力、勁度、振頻與模態、挫曲負載與模態、強度)具偵測與控制前述力學行為功能之智慧結構的分析與設計、對受損複材結構加以修補之設計與分析，這些分工以各個子計劃分別進行；同時總計劃則進行協調合作討論、對各子計劃之工作和成果內容加以規範與整合，達成建立一套能用而有效之整合系統，可真正應用於針對複材結構受損後之各種力學行為分析，並對此行為之智慧監控、和修補之分析設計