Source: http://www.asmscience.org/content/concept/Entity/ASM/Microbiology/Cell_and_Molecular_Microbiology/Cellular_Processes/Secretion_Systems/Bacterial_Secretion_Systems/Gram-Negative_Bacteria_Secretion_Systems/Type_II_Secretion_System
Timestamp: 2019-04-26 00:11:24+00:00

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NOD-like receptor (NLR) proteins, as much as Toll-like receptor proteins, play a major role in modulating myeloid cells in their immune functions. There is still, however, limited knowledge on the expression and function of several of the mammalian NLR proteins in myeloid lineages. Still, the function of pyrin domain-containing NLR proteins and NLRC4/NAIP as inflammasome components that drive interleukin-1β (IL-1β) and IL-18 maturation and secretion upon pathogen stimulation is well established. NOD1, NOD2, NLRP3, and NLRC4/NAIP act as bona fide pattern recognition receptors (PRRs) that sense microbe-associated molecular patterns (MAMPs) but also react to endogenous danger-associated molecular patterns (DAMPs). Ultimately, activation of these receptors achieves macrophage activation and maturation of dendritic cells to drive antigen-specific adaptive immune responses. Upon infection, sensing of invading pathogens and likely of DAMPs that are released in response to tissue injury is a process that involves multiple PRRs in both myeloid and epithelial cells, and these act in concert to design tailored, pathogen-adapted immune responses by induction of different cytokine profiles, giving rise to appropriate lymphocyte polarization.
This chapter integrates unpublished data with the published reports on the synergism between veillonellae and streptococci. It speculates on how the genome sequence of veillonellae will help one understand its biology and potential role in the pathogenicity of the dental biofilm community. It was discovered that hydrogen peroxide (H2O2) resistance in Streptococcus mutans was increased 100 to 1,000-fold over monospecies culture in cocultures with Veillonella sp. strain PK1910. This chapter focuses on some important findings from the Veillonella sp. strain PK1910 genome. In the 1964 description of Veillonellasp. by Rogosa, the species V. alcalescens was distinguished from V. parvula by the ability to decompose H2O2. In the 1982 revision of the species, the former subspecies in V. alcalescens were classified as three species: V. ratti, V. criceti, and V. dispar. Veillonella species are among the most prevalent early colonizers of oral biofilm. In-depth investigations on the mechanism of interactions of veillonellae with other oral microbial species will contribute significantly to one&apos;s overall understanding of the ecology of oral biofilms in the human host. Different from a metagenomics approach, metatranscriptomics focuses on community member functions at a particular time under a particular condition.
Bacterial lipoproteins represent a unique class of membrane proteins, which are anchored to membranes through triacyl chains attached to the amino-terminal cysteine. They are involved in various functions localized in cell envelope. Escherichia coli possesses more than 90 species of lipoproteins, most of which are localized in the outer membrane, with others being in the inner membrane. All lipoproteins are synthesized in the cytoplasm with an N-terminal signal peptide, translocated across the inner membrane by the Sec translocon to the periplasmic surface of the inner membrane, and converted to mature lipoproteins through sequential reactions catalyzed by three lipoprotein-processing enzymes: Lgt, LspA, and Lnt. The sorting of lipoproteins to the outer membrane requires a system comprising five Lol proteins. An ATP-binding cassette transporter, LolCDE, initiates the sorting by mediating the detachment of lipoproteins from the inner membrane. Formation of the LolA-lipoprotein complex is coupled to this LolCDE-dependent release reaction. LolA accommodates the amino-terminal acyl chain of lipoproteins in its hydrophobic cavity, thereby generating a hydrophilic complex that can traverse the periplasmic space by diffusion. Lipoproteins are then transferred to LolB on the outer membrane and anchored to the inner leaflet of the outer membrane by the action of LolB. In contrast, since LolCDE does not recognize lipoproteins possessing Asp at position +2, these lipoproteins remain anchored to the inner membrane. Genes for Lol proteins are widely conserved among gram-negative bacteria, and Lol-mediated outer membrane targeting of lipoproteins is considered to be the general lipoprotein localization mechanism.
Typically, the biotechnological basis for strain improvement to enhance recombinant protein production relies on the permanent implementation of desirable traits into the production strain to stimulate both cell growth and functional expression of the target gene during the cultivation. This chapter reviews the major technical issues associated with Escherichia coli strain engineering to enhance recombinant protein production and directs the reader to protocols appropriate for specific applications. Theoretically, strategies based on enhancing the limiting step can lead to an overall improvement in recombinant protein production. Stationary-phase genes encode proteins that may lead to a reduction in cellular and metabolic activity, which can negatively affect recombinant protein production, and as such, these genes are targets for strain improvement. The recently commercialized recombineering protocol from Gene Bridges, also based on λ Redmediated recombination, allows versatile chromosomal engineering, including gene disruption, deletion, insertion, point mutation, modification, and even promoter fine-tuning, and can serve as a versatile manipulation tool for strain improvement and even optimization. The general guidelines for strain improvement are (i) to ensure the genetic stability of the host/vector system, (ii) to maximize the synthesis fluxes for all the gene expression steps (i.e., transcription, translation, and posttranslational processing steps), (iii) to ensure the flux balance of these protein synthesis steps, (iv) to stabilize all the expression intermediates and final products, and (v) to minimize the physiological impact associated with high-level gene expression and high-cell density cultivation.
This chapter discusses the insights into pathogenicity and the wider processes of Escherichia coli genome evolution that have resulted from the sequencing of the E. coli K-12 genome, and, more recently, those from a number of pathogenic E. coli strains, including several from the related “genus” Shigella. It also discusses the available resources for E. coli genomics and the progress that has been made in recent years toward a complete understanding of E. coli biology. Genes that are acquired by horizontal transfer subsequently undergo a process of amelioration as their base composition becomes acclimatized to the new host. Programs such as BLAST can be used to identify unexpected similarities between genes in phylogenetically distinct species, although it should be noted that BLAST results do not necessarily correspond to those from more robust phylogenetic analyses. Interestingly, strains classified as group B2 are rarely found as human commensals, and the group includes many strains with extraintestinal pathogenic E. coli (ExPEC) virulence determinants. As with enterohemorrhagic E. coli (EHEC) O157:H7, Shigella flexneri serotype 2a was an obvious target for whole-genome sequencing because of its importance as a pathogen. The processes of E. coli genome evolution are clear from the genome sequences already available.

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