9.3.pdf

Yogurt, pickles, sauerkraut, and lime dishes taste tangy due to their high acidity, measured by pH. Acidity affects macromolecules like DNA, lipids, and proteins. pH Basics: ○ pH < 7.0: Acidic ○ pH > 7.0: Basic ○ pH affects macromolecule structure:...

Yogurt, pickles, sauerkraut, and lime dishes taste tangy due to their high acidity, measured by pH. Acidity affects macromolecules like DNA, lipids, and proteins. pH Basics: ○ pH < 7.0: Acidic ○ pH > 7.0: Basic ○ pH affects macromolecule structure: High pH can break DNA bonds. Extreme basicity can break down lipids. Proteins are very sensitive to pH changes, affecting their shape and function. Growth pH: ○ Optimum Growth pH: Best pH for organism growth. ○ Minimum Growth pH: Lowest tolerable pH. ○ Maximum Growth pH: Highest tolerable pH. ○ Example: Salmonella spp. optimum pH is 7.0–7.5, minimum is around 4.2. Microorganism Preferences: ○ Neutrophiles: Most bacteria (e.g., E. coli, Salmonella) thrive near pH 7.0; they struggle in acidic environments. ○ Fungi: Prefer slightly acidic pH (5.0–6.0). ○ Acidophiles: Prefer pH < 5.55 (e.g., Sulfolobus spp. thrive at pH 2.5–3.5; Ferroplasma at pH 0–2.9). ○ Lactobacillus: Important for vaginal acidity (pH ~4), helps inhibit other microbes. ○ Alkaliphiles: Prefer pH 8.0–10.5 (e.g., Vibrio cholerae thrives at pH 8.0, survives pH 11.0). Adaptations: ○ Acidophiles have proteins that are stable in low pH and pump out H+ ions to survive. ○ Alkaliphiles adapt their lipid and protein structures to thrive in high pH.