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Related Concept Videos

Exocrine Glands: Types of Secretions01:13

Exocrine Glands: Types of Secretions

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Exocrine glands produce and release a variety of glandular products. Exocrine glands can be classified into serous, mucous, or mixed types based on their secretory products.
Serous glands produce watery secretions rich in digestive enzymes and proteins. The constituent cells of the serous gland have centrally located nuclei and eosinophilic secretory granules in the cytoplasm. The parotid gland is an example of a serous gland. It secretes saliva, which contains enzymes, such as lipases and...
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Gram-negative Bacterial Protein Secretion Systems01:17

Gram-negative Bacterial Protein Secretion Systems

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Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular environment or host cells. Based on their mechanism of action, these systems are classified into one-step and two-step pathways.One-Step Secretion Systems (Types I, III, IV, and VI)One-step secretion systems bypass the periplasm entirely, forming a continuous channel that spans both the inner and outer membranes:Type I Secretion System (T1SS):...
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Second Order systems II01:18

Second Order systems II

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In an underdamped second-order system, where the damping ratio ζ is between 0 and 1, a unit-step input results in a transfer function that, when transformed using the inverse Laplace method, reveals the output response. The output exhibits a damped sinusoidal oscillation, and the difference between the input and output is termed the error signal. This error signal also demonstrates damped oscillatory behavior. Eventually, as the system reaches a steady state, the error diminishes to zero.
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Hormones Secreted by the Stomach01:25

Hormones Secreted by the Stomach

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Enteroendocrine cells, accounting for only 1% of stomach epithelial cells, play a significant role in digestion and are classified by their digestive hormone secretions.
Each of these hormones secreted by different enteroendocrine cells plays a unique role in digestion. Here are a few examples:
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Pancreatic Juice and Secretion01:26

Pancreatic Juice and Secretion

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Pancreatic juice is a clear fluid produced by the pancreas, containing water, salts, sodium bicarbonate, and enzymes vital for digestion in the small intestine. It helps break down large molecules, facilitating nutrient absorption.
When acidic chyme from the stomach enters the duodenum, it triggers the release of secretin, a hormone that prompts pancreatic juice secretion. After a fatty meal, cholecystokinin, another hormone, stimulates gallbladder contraction and enhances enzyme-rich...
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Tubular Reabsorption and Secretion01:28

Tubular Reabsorption and Secretion

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Tubular secretion and reabsorption are two critical processes in the nephron tubule of the kidneys. When the fluid filtered from the glomerulus enters the proximal convoluted tubule, it is referred to as filtrate, and its composition changes due to tubular reabsorption and secretion.
Tubular reabsorption is a selective process that starts when the filtrate enters the proximal tubules. It involves substances traveling through the transcellular route (through the tubule cell and peritubular...
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Related Experiment Video

Updated: Jan 28, 2026

Analysis of Interactions between Endobiotics and Human Gut Microbiota Using In Vitro Bath Fermentation Systems
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Type VI Secretion Systems and the Gut Microbiota.

Michael J Coyne1, Laurie E Comstock1

  • 1Division of Infectious Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.

Microbiology Spectrum
|March 3, 2019
PubMed
Summary

Gut bacteria use type VI secretion systems (T6SSs) to compete. This review explores T6SSs in human gut Bacteroidales, focusing on their genetic diversity and antagonistic functions against other bacteria.

Area of Science:

  • Microbiology
  • Gut Microbiome Research
  • Bacterial Interactions

Background:

  • The human colon harbors a complex microbial ecosystem with extensive inter-species competition.
  • Gut bacteria employ various antagonistic mechanisms, including type VI secretion systems (T6SSs), to outcompete rivals.
  • While T6SSs are known in Proteobacteria like Escherichia coli, their role in Bacteroidales, a dominant Gram-negative gut group, is increasingly recognized.

Purpose of the Study:

  • To review the properties and ecological significance of T6SSs in human gut Bacteroidales.
  • To examine the genetic diversity of T6SS loci (GA1, GA2, GA3) within Bacteroidales.
  • To understand the antagonistic capabilities of T6SSs, particularly GA3, against other gut bacteria.

Main Methods:

  • Literature review focusing on T6SSs in human gut Bacteroidales.

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  • Analysis of genetic architectures (GA1, GA2, GA3) of T6SS loci.
  • Examination of effector and immunity proteins encoded by T6SS divergent regions.

    • Main Results:

    • T6SS loci are widespread in human gut Bacteroidales, with three distinct genetic architectures (GA1, GA2, GA3).
    • GA1 and GA2 T6SS loci are transferable via integrative and conjugative elements, facilitating horizontal gene transfer among Bacteroidales.
    • GA3 T6SSs, exclusive to Bacteroides fragilis, demonstrate broad antagonism against numerous gut Bacteroidales species.

    Conclusions:

    • T6SSs play a crucial role in the competitive dynamics of the human gut microbiota, particularly within the Bacteroidales order.
    • The genetic diversity and transferability of T6SS loci suggest significant ecological adaptation and evolution within this gut bacterial group.
    • Further research into T6SS effector mechanisms and in vivo ecological outcomes is warranted to fully understand their impact on gut health.