Saran's Learn Microbiology

  Category Examples Typical Microorganisms Main Source of Contamination Type of Spoilage Notes Raw Plant Foods Fruits, vegetables, grains, nuts Pseudomonas, Erwinia, Bacillus, yeasts (Saccharomyces), molds (Penicillium, Aspergillus) Soil, air, water, harvesting & handling Soft rot, souring, discoloration, mold growth High moisture → rapid spoilage Raw Animal Foods Meat, fish, milk, eggs Pseudomonas, Lactobacillus, Salmonella, Staphylococcus, Vibrio, molds Slaughtering, skin, intestine, equipment Off-odors, slime, rancidity, putrefaction High protein & aw → supports bacterial growth Pasteurized Foods (Heat processed) Pasteurized milk, soups, juices Surviving thermoduric bacteria, post-contamination coliforms, yeasts Improper heat / post-p...

  Helicobacteria ·        Heliobacteria are Gram-positive, endospore-forming, anoxygenic phototrophic bacteria found in anaerobic soils and paddy fields. ·        Example – Heliobacterium chlorum , Heliobacillus mobilis , Heliospirillum photoanaerobium and Heliomicrobium modesticaldum . ·        Number of Species – There are over 40 validated species within the Helicobacter genus, with new species occasionally being discovered in different animal hosts. ·        Habitat – Soil, paddy fields, hot springs, alkaline soils, anaerobic mud, soda lakes; commonly found in waterlogged agricultural fields (especially rice field). ·        Mode of Nutrition – Photoheterotrophic, require organic carbon sources and use light as an energy source. ·        Mode of Reproduction – Reproduce asexually via Binary fis...

Green Non-Sulfur Bacteria ·        Example – Chloroflexus aurantiacus , Chloronema giganteum , Oscillochloris trichoides and Herpetosiphon aurantiacus. ·        Number of Species – Around 30 – 35 species. ·        Habitat – Hot springs, alkaline springs, marine sediments, microbial mats, geothermal areas; thrive in hot, low-oxygen, illuminated environments. ·        Mode of Nutrition ü   Photoheterotrophy (Primary Mode): They preferentially use light for energy but require organic compounds (e.g., sugars, amino acids, organic acids) as carbon sources. ü   Photoautotrophy (Alternative Mode): Some, like Chloroflexus, can fix CO ₂ , but they use a unique pathway called the 3-Hydroxypropionate pathway, which is different from the Calvin cycle (used by plants and purple bacteria) and the rTCA cycle (used by green sulfur bacteria). ü   Chemoheterotrophy:...

  Green Sulfur Bacteria ·        Example – Chlorobium limicola , Chlorobaculum tepidum , Prosthecochloris aestuarii and Pelodictyon luteolum. ·        Number of Species – Over 90 species, found mainly in the family Chlorobiaceae. ·        Habitat ü   Anaerobic zones of lakes and ponds, sulfur-rich environments, stagnant waters, sulfur springs, marine sediments. ü   Live in deep, low-light zones where H ₂ S is abundant. ·        Mode of Nutrition – Obligate photoautotrophs ( use light as energy and CO ₂ as carbon source). ·        Mode of Reproduction – Binary fission (Asexual mode) ·        Mode of Respiration – Obligate anaerobes (cannot survive in presence of oxygen). ·        Type of Photosynthesis – Anoxygenic photosynthesis (do not use water as an elect...