Gram-negative bacteria have evolved several secretory pathways to release proteins or toxic factors into their surrounding environment. Many virulence determinants, including extracellular toxins and proteases, are secreted by the type II secretion system (T2SS) which is widely conserved and common among γ-proteobacteria.

Typical T2SSs are composed of 12 to 16 proteins termed Gsp (General secretion pathway) proteins. These components associate in a multiprotein complex that constitutes a large structure (the secreton) that spans the periplasm and is thought to connect inner and outer membranes. Exoproteins that use the T2SS are characterized by the presence of a leader peptide (or signal peptide) at their N terminus and are secreted in the extracellular medium by a two-step process involving a transient periplasmic intermediate. The T2SS is unique in its ability to promote secretion of large multimeric proteins that are folded in the periplasm. The system is also characterized by a species-specificity, which is mainly related to the GspC and GspD components, the gatekeepers.

Although relatively little attention has been payed to the regulation of T2SSs, it was observed that expression of most of the genes encoding T2SS-dependent exoproteins is growth phase-dependent or strictly regulated by environmental signals. In Pseudomonas aeruginosa, T2SS assembly and most of the T2SS-dependent exoproteins are regulated via quorum sensing, a mechanism that senses the density of a surrounding bacterial population.

Besides typical T2SSs, some secretory systems are found which contain all the T2SS components but in a different genetic organization. Some incomplete systems have also been described which contain genes homologous to T2SS but dispersed on the bacterial chromosome. Components of these systems can either associate with classical T2SS components to constitute a functional hybrid machinery or represent peculiar systems with strictly defined functions.

from Michel and Voulhoux in Bacterial Secreted Proteins

Further reading:

1. Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis
2. Pseudomonas: Genomics and Molecular Biology
3. Microbial Toxins: Current Research and Future Trends

Labels: bacteria, protein, protein secretion, proteins, Pseudomonas, toxin

Bacteria have developed numerous systems to secrete proteins or DNA in order to modify their immediate surroundings or to obtain an advantage in a competitive and hostile environment. Since Gram-negative bacteria possess two membranes, the inner (cytoplasmic) membrane and the outer membrane, transport machines for protein secretion have the challenging task of circumventing two barriers to reach the exterior. A rather simple transport apparatus, the Type I secretion machinery, composed of only three proteins residing in the inner and outer membrane of Gram-negative bacteria achieve this objective in a single step. The Type I secretion pathway although also present in Gram-positive bacteria, has been analysed in greatest detail in Gram-negative bacteria. Almost all Type I transport substrates are polypeptides, varying from the small Escherichia coli peptide colicin V, (10 kDa) to the large Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa. While these two examples reflect the range of the size of Type I transport substrates, the best characterized are the RTX toxins and the lipases. Type I secretion is also involved in export of non-proteinaceous substrates like cyclic β-glucans or polysaccharides.

from Jenewein et al in Bacterial Secreted Proteins

Further reading:

1. Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis
2. Pseudomonas: Genomics and Molecular Biology
3. Microbial Toxins: Current Research and Future Trends

Labels: bacteria, protein, protein secretion, proteins, Pseudomonas, toxin

A number of book reviews on microbiology books have been published recently. Extracts provided below:

BACILLUS: CELLULAR AND MOLECULAR BIOLOGY
"The quality of the chapters is uniformly high. Together they provide a review of significant progress toward a better and deeper understanding of the physical structure and molecular biological organization and function in Bacillus subtilis. As a consequence, a truly intimate grasp of this bacterium is achieved." from The Quarterly Review of Biology
Further information: BACILLUS

REAL-TIME PCR IN MICROBIOLOGY: FROM DIAGNOSIS TO CHARACTERIZATION
"... enjoyable and easy to read ... well-referenced and provide an easy to follow explanation, especially the chapter on fluorogenic chemistry which also has clear illustrations. The table of design rules for oligonucleotide and probes provided a good summary in an easy-to-read format. ... an interesting insight into the thoughts of the current leaders in their fields. This book shows what a versatile and sensitive tool real-time PCR can be and the many uses it can be put too. In my opinion this book would be useful for the novice because of the background information it provides." from Microbiology Today
Further information: REAL-TIME PCR

PSEUDOMONAS: GENOMICS AND MOLECULAR BIOLOGY
"... the contribution by Fajardo & Martinez on antibiotic resistance provides a wealth of background information on this clinically relevant topic ... the contributions by Haussler and Klockgether et al. give insight into recent progress made in the areas of small colony variants and genome diversity of P. aeruginosa, respectively. Three other chapters provide useful complementary information ... Institutions with an interest in Pseudomonas research should consider acquiring this book." from Microbiology Today
Further information: PSEUDOMONAS

MOLECULAR ORAL MICROBIOLOGY
"... a broad and comprehensive text covering the molecular aspects of dental caries and periodontal disease. Accompanying each of the fully referenced chapters are detailed illustrations and the inclusion of high-quality colour equivalents of these figures at the end of the book is welcome. ... of value to all microbiologists with an interest in molecular microbiology ... excellent overview of current methodologies ... appeal to dental undergraduates and postgraduates." from Microbiology Today
Further information: ORAL MICROBIOLOGY

EPIGENETICS
"... a significant collection of articles, relating to various aspects of epigenetics. The text is clear and concise and all reports include accurate data and figures. ... will assist researchers in the field and provides an important introductory reference for scientists that want to embark on such research. It is highly recommended for personal and institutional purchase." from Microbiology Today
Further information: EPIGENETICS

Labels: bacillus, book review, epigenetics, oral microbiology, Pseudomonas, real-time PCR