Project description:Whole-genome sequencing is an important way to understand the genetic information, gene function, biological characteristics, and living mechanisms of organisms. There is no difficulty to have mega-level genomes sequenced at present. However, we encountered a hard-to-sequence genome of Pseudomonas aeruginosa phage PaP1. The shotgun sequencing method failed to dissect this genome. After insisting for 10 years and going over 3 generations of sequencing techniques, we successfully dissected the PaP1 genome with 91,715 bp in length. Single-molecule sequencing revealed that this genome contains lots of modified bases, including 51 N6-methyladenines (m6A) and 152 N4-methylcytosines (m4C). At the same time, further investigations revealed a novel immune mechanism of bacteria, by which the host bacteria can recognize and repel the modified bases containing inserts in large scale, and this led to the failure of the shotgun method in PaP1 genome sequencing. Strategy of resolving this problem is use of non-library dependent sequencing techniques or use of the nfi- mutant of E. coli DH5M-NM-1 as the host bacteria to construct the shotgun library. In conclusion, we unlock the mystery of phage PaP1 genome hard to be sequenced, and discover a new mechanism of bacterial immunity in present study. Methylation profiling of Pseudomonas aeruginosa phage PaP1 using kinetic data generated by single-molecule, real-time (SMRT) sequencing on the PacBio RS.
Project description:The aim of this project is to identify, by bottom-up proteomic analysis, one or both representatives of two classes of 8-vinyl reductase in an Acaryochloris marina cell lysate. This enzyme is responsible for the conversion of the C8 vinyl group in the chlorophyll precursor Mg-divinyl-protochlorophyllide to ethyl as part of the chlorphyll biosynthesis pathway. Both putative 8VRs, NmrA and FrhB were detected.
Project description:Ancient oxygenic photosynthetic prokaryotes produced oxygen as a waste product, but existed for a long time under an oxygen-free (anoxic) atmosphere, before an oxic atmosphere emerged. The change in oxygen levels in the atmosphere influenced the chemistry and structure of many enzymes that contained prosthetic groups that were inactivated by oxygen. In the genome of Acaryochloris marina, multiple gene copies exist for proteins that are normally encoded by a single gene copy in other cyanobacteria. Using high throughput RNA sequencing to profile transcriptome responses from cells grown under microoxic and hyperoxic conditions, we detected 8446 transcripts out of the 8462 annotated genes in the Cyanobase database. Two thirds of the 50 most abundant transcripts are key proteins in photosynthesis. Microoxic conditions negatively affected the levels of expression of genes encoding photosynthetic complexes, with the exception of some subunits. In addition to the known regulation of the multiple copies of psbA, we detected a similar transcriptional pattern for psbJ and psbU, which might play a key role in the altered components of photosystem II. Furthermore, regulation of genes encoding proteins important for reactive oxygen species-scavenging is discussed at genome level, including, for the first time, specific small RNAs having possible regulatory roles under varying oxygen levels.
Project description:Many, if not all, bacteria use quorum sensing (QS) to control gene expression and collective behaviours, and more recently QS has also been discovered in bacteriophages (phages). Phages can produce communication molecules of their own, or “listen in” on the host’s communication processes, in order to switch between lytic and lysogenic modes of infection. In this project, we studied the interaction of Vibrio cholerae, the causative agent of cholera disease, with the lysogenic vibriophage VP882. The lytic cycle of VP882 is induced by the QS molecule DPO (3,5-dimethylpyrazin-2-ol), however, the global regulatory consequences of DPO-mediated VP882 activation have remained unclear. Using a combination of transcriptomic, genetic, and biochemical approaches, we discovered that induction of VP882 results in binding of phage transcripts to the major RNA chaperone Hfq, which in turn outcompete and down-regulate host-derived Hfq-dependent small RNAs (sRNAs). VP882 itself also encodes Hfq-binding sRNAs and we demonstrate that one of these sRNAs, named VpdS, modulates the expression of multiple host and phage mRNAs through a base-pairing mechanism and thereby promotes phage replication. We further show that host-derived sRNAs can affect phage replication by interfering with the translation of phage mRNAs and thus might be part of the phage defence arsenal of the host. Taken together, our data draw a complex picture of post-transcriptional interactions occurring between host- and phage-derived transcripts that together determine the phage-mediated lysis program.