Bacterial Secretion and TCS Mechanisms

Secretion Mechanisms in Bacteria

• Bacterial proteins can be secreted to the cell surface or the external environment, differentiated by their purpose and mechanism.
• Surface secretion (e.g., Gram-positive bacteria using sortases) anchors proteins to the cell wall for adhesion, immune evasion, or interaction with the host.
• External secretion (e.g., Type 1, Type 3 secretion systems in Gram-negative bacteria) releases proteins into the environment to interact with the host or disrupt its environment, often using specialized protein secretion machinery.

Two-Component Signal Transduction Systems (TCSs) in Bacteria

• Bacteria use TCSs to detect external stimuli and respond.
• A stimulus activates a histidine kinase in the membrane.
• The kinase autophosphorylates and transfers the phosphate to a response regulator in the cytoplasm.
• The phosphorylated response regulator regulates gene expression (activating or repressing transcription).
• This allows bacteria to adapt to changing environmental conditions, including quorum sensing in biofilms.

Microbial Interactions with Hosts - Beneficial, Opportunistic, and Pathogenic

• Beneficial microbes are essential parts of the microbiome, contributing positively to health (e.g., gut microbes competing with pathogens).
• Opportunistic microbes cause infections when the host's defenses are weakened (e.g., opportunistic infections by Pseudomonas in immunodeficient individuals).
• Pathogenic microbes actively cause disease in healthy individuals (e.g., Vibrio cholerae causing severe diarrhea).

Viral Interactions with Host Cells

• Viruses exploit host mechanisms for infection.
• Viruses attach to host receptors and enter cells via endocytosis or membrane fusion.
• Viruses use host cellular machinery for replication and protein synthesis.
• Viruses manipulate host systems to enhance their replication and spread, example HIV and its manipulation of host protein machinery.

Microbial Interactions with the Environment: Examples

• Marine microbes exhibit complex symbiotic relationships, e.g., bioluminescent bacteria with squid. Marine viruses recycle nutrients.
• Biofilms demonstrate intricate interspecies communication and influence environmental processes (e.g., nutrient cycling, biofouling).

Microbial Interactions with the Human Host: Examples

• Normal gut microbiota degrade nutrients, produce essential vitamins, and inhibit the growth of harmful microbes.
• Pathogens like EPEC use specialized secretion systems to interact with host cells.
• Streptococcus mutans contributes to tooth decay through acid production.
• Dysbiosis occurs when antibiotic use disrupts the microbiome, contributing to pathogenic overgrowth in the human body.

Test your knowledge on the secretion mechanisms of bacterial proteins and two-component signal transduction systems (TCSs). Understand how bacteria communicate with their environment and adapt to stimuli through these complex processes. This quiz covers key concepts related to bacterial functionality and interaction.