Forensics Biology

• Forensic Environmental Profiling uses the presence of certain proxy indicators which are fragments of the original environment to assess the environment
• Proxy indicators used in Forensic Environmental Profiling

  • Bacteria
  • Pollen
  • Algae
• Applying Forensic Environmental Profiling

  1. Using a range of biological, geological & sedimentological techniques to identify different types or species

  2. Interpretation of the environmental profile in a forensic context
• Prokaryotes


  Bacteria & Archaea
• Archaea were classified as a separate domain in 1977
• Prokaryotic cells


  • Single-celled, without a nucleus, more diverse than Eukaryotes
  • No nucleus (DNA bound with proteins forming amorphous nucleoid)
  • No membrane-bound organelles
  • Have a cell wall
• Eukaryotic cells


  • DNA in the nucleus
  • Contain membrane-enclosed organelles (mitochondria, chloroplasts, plastids, golgi complex, etc)
• Microbiology


  The study of microorganisms
• Microorganisms


  • Single cell microscopic organisms (included single celled eukaryotes e.g. yeasts and algae (diatoms), as well as viruses)
• Microorganisms are only visible with a microscope
• In 1 mm^3 there can be around 1,000,000,000 bacterial cells
• Microbial carbon sources


  • Autotrophs: build their cellular structures from CO2
  • Heterotrophs: obtain C by breaking down complex organic compounds
• Microbial energy sources


  • Light
  • Inorganic chemicals
  • Organic compounds
• Microbial oxygen requirements


  • Aerobic
  • Anaerobic
• Bacterial division


  1. Replication of DNA

  2. Division into two cells
• Under ideal conditions, E. coli divides every 20 minutes, resulting in 2 x 10^21 cells after 24 hours
• Microbial classification and identification methods


  • Macroscopic features (colony shape, size, colour, smell)
  • Microscopic features (rods, cocci, spiral, chain forming, flagella)
  • Staining techniques (gram staining, endospore staining)
  • Physiological requirement assessment (aerobic/anaerobic, growth on substrates)
  • Biochemical tests (catalase, oxidase, fatty acid profiling, secondary metabolite profiles, immunological testing)
  • DNA testing (16S rRNA sequencing, metagenomics)
• Bacterial morphology


  • Bacillus (rod)
  • Cocci (spherical)
  • Spirillum (spiral)
  • Spirochaetes (corkscrew)
  • Vibrio (comma)
• Flagella


  • Helical and rotate like propellers, can propel cells through liquid at up to 60 cell lengths/sec
• Fimbriae


  • Enable cells to stick to surfaces and form biofilms
• Pili


  • Similar to fimbriae but longer, facilitate genetic exchange between cells
• Endospores


  Highly differentiated cells containing dehydrated cytoplasm, DNA, ribosomes and enzymes, with a protective cortex and coat
• Endospore formation


  1. Survival structures formed after nutrient depletion or to endure extremes of temperature and drying

  2. Dormant stage of bacterial life cycle

  3. Extremely resistant to heat, desiccation, chemicals, radiation

  4. Easily dispersed by wind, water or through animal gut

  5. Require only water to reinitiate vegetative growth
• Studies claim endospores can remain viable even after millions of years
• Gram-positive bacteria


  Have a thick peptidoglycan layer
• Gram-negative bacteria


  Have 2 cytoplasmic membranes (inner and outer) separated by periplasm, with a thin layer of peptidoglycan
• Gram-positive bacteria stain purple, Gram-negative bacteria stain pink with Gram stain
• In 1 g of temperate soil there can be over 1 billion microbial cells belonging to over 1,000 different species
• Microbial communities


  Microorganisms in nature are members of complex microbial communities, competing for nutrients and space
• The environment microorganisms inhabit depends on temperature, pH, salinity, pressure, nutrient availability and their metabolic capabilities
• The human body is a rich microbial habitat, with the gut containing the most microorganisms
• The human microbiome contains 40 trillion microbial cells, around 1.3 times the number of human cells, and makes up 1-3% of the body's mass
• Normal microflora


  Most, but not all, microorganisms in the human body are benign
• Microorganisms are involved in processes like digesting food and producing vitamins, and may influence susceptibility to diseases, disorders like obesity and diabetes, and response to drug treatments
• Microbiome transplants are used to combat illnesses like Clostridium difficile infections by establishing healthier bacterial populations
• Roles of microorganisms in the environment


  • Decompose organic material
  • Contribute to C, N, S, P cycles
  • Produce biofuels
  • Clean up pollutants
• Alcoholic beverages and baked goods rely on the fermentative activities of yeast (Saccharomyces cerevisiae)
• Fermentation


  Generates alcohol and carbon dioxide (CO2), producing alcohol in beer and wine, and raising dough in bread
• In industrial microbiology, microorganisms are grown on a large scale to produce antibiotics, enzymes, and various chemicals
• In biotechnology, genetically engineered microorganisms are used to synthesize products of high commercial value, such as human proteins and hormones