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Related Concept Videos

Formation of Lipopolysaccharides01:19

Formation of Lipopolysaccharides

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Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin,...
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Peptidoglycan Synthesis01:28

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Structure of PeptidoglycanPeptidoglycan is a vital structural component of the bacterial cell wall, providing mechanical strength and shape to the cell. It consists of repeating units of two sugars—N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)—linked by β-1,4 glycosidic bonds. These sugar chains are cross-linked by short peptide chains, forming a mesh-like polymer that surrounds the bacterial plasma membrane.Cytoplasmic Phase – Precursor SynthesisPeptidoglycan...
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Bacterial cells were initially considered simple, randomly organized structures lacking a cytoskeleton. However, the discovery of cytoskeleton homologs in bacteria led to the change of this opinion. Bacterial cytoskeletal filaments regulate the cell shape, cell polarity, cell division, and partitioning of plasmids during cell division. It was later discovered that bacterial cytoskeletal proteins, mainly actin and tubulin homologs, are diverse compared to their eukaryotic counterparts. On the...
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Oligosaccharide Assembly01:24

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Protein glycosylation starts in the ER lumen and continues in the Golgi apparatus. Glycosyltransferases catalyze the addition of sugar molecules or glycosylation of proteins. Usually, these enzymes add sugars to the hydroxyl groups of selected serine or threonine residues to form O-linked glycans or the amino groups of asparagine residues to form N-linked glycans. Different positions on the same polypeptide chain can contain differently linked glycans.
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Related Experiment Video

Updated: Sep 16, 2025

Author Spotlight: Advancing Research in Microbial Autoaggregation Using Imaging Flow Cytometry
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Author Spotlight: Advancing Research in Microbial Autoaggregation Using Imaging Flow Cytometry

Published on: September 29, 2023

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Auto-aggregation in Streptococcus intermedius is driven by the Pel polysaccharide.

Deepa Raju1, Siobhán A Turner1, Karla Castro1,2

  • 1Program in Molecular Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada.

Mbio
|July 7, 2025
PubMed
Summary

Streptococcus milleri group bacteria use Pel polysaccharide production for biofilm formation and infection persistence. This study identifies key genes involved in Pel biosynthesis, revealing its role in S. intermedius pathogenicity and host immune modulation.

Keywords:
BiofilmPel exopolysaccharideS. intermediusaggregationhost immune responsesinfection

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Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Molecular Biology

Background:

  • The Streptococcus milleri group (SMG) comprises opportunistic pathogens causing diverse infections.
  • Pathogenic mechanisms in SMG, particularly auto-aggregation and biofilm formation, are poorly understood.
  • Auto-aggregation is crucial for biofilm adhesion and cohesion in many bacterial species.

Purpose of the Study:

  • To investigate the role of Pel exopolysaccharide production in Streptococcus intermedius biofilm formation and pathogenicity.
  • To identify and characterize genes involved in Pel biosynthesis in S. intermedius.
  • To understand how Pel production influences bacterial persistence and host immune interactions.

Main Methods:

  • Identification of a S. intermedius gene cluster homologous to Bacillus cereus and Pseudomonas aeruginosa pel operons.
  • Characterization of clinical S. intermedius isolates for aggregation and biofilm phenotypes.
  • Genetic manipulation (gene deletion) to assess the function of identified genes in aggregation and Pel production.
  • Biochemical analysis to identify the composition of the aggregated polymer.
  • In vivo assessment using a mouse abscess model to evaluate the impact of Pel production on infection clearance.

Main Results:

  • A S. intermedius gene cluster containing five canonical pel genes (pelDEADAFG) and four additional genes was identified.
  • Aggregation phenotype in S. intermedius strain C1365 was dependent on the pelDEADAFG genes.
  • Deletion of two additional genes (SIR_1592 and SIR_1594) partially reduced aggregation.
  • SIR_1591 was identified as a glycoside hydrolase, and C1365 produces a GalNAc-rich polymer.
  • Loss of Pel production in a ΔpelF mutant resulted in more effective bacterial clearance in a mouse abscess model.
  • Pel production modulates S. intermedius interaction with the host immune system.

Conclusions:

  • Pel exopolysaccharide biosynthesis is a significant contributor to S. intermedius pathogenicity.
  • Pel production enhances bacterial persistence during infection and influences host immune responses.
  • The identified pel gene cluster, including canonical and additional genes, plays a critical role in S. intermedius aggregation and biofilm formation.