Microbes

• Microbes are:

  • Bacteria
  • Archaea
  • Fungi
  • Protozoa
  • Viruses
  • [Micro] Algae
  • [Some] Animals

  Does not include viruses

  ~70-90% marine life [by mass] estimated to be microbial
• Prokaryote vs Eukaryote


  Key differences:

  
• Bacteria


  Ancestors are oldest forms

  • Earth ~4.5 billion years old
  • Bacteria/archaea ~4 billion
  • Multicellular macroscopic life ~1 billion

  Cyanobacteria change atmosphere - Great Oxidation Event ~2.4 billion years old

  Found in all environments - estimated biomass ~70 Gt C

  Fundamental to life on earth, have a wide range of morphologies and use a wide range of energy sources:

  • Light (phototrophy)
  • Organic compounds (organotrophy)
  • Inorganic compounds (lithotrophy)

  
• Bacteria - Morphology

  • Cell wall – provides structure andrigidity; relatively porous, provides someprotection but small substrates cancross
  • Cell membrane – phospholipid bilayer,similar to eukaryotes; acts as apermeability barrier
  • Cytoplasm – contains chromosomal DNA,plasmids, and ribosomes
  • Pili/Fimbriae – hair-like protein tubes forattachment to surfaces and to otherbacteria; can be used to transferplasmids
  • Flagella – for locomotion; spins in theorder of hundreds of rpm
  • Reproduce asexually through fission
  • Horizontal gene transfer allowsevolution

  
• Bacteria - free-living behaviour

  Not all motile, but many are:

  • Free-living bacteria may produce biofilms
  • Release compounds detectable by other bacteria - quorum sensing - causes a switch from planktonic swimming [drifting] to benthic sessile lifestyle
  • Biofilms rely on Extracellular Polymeric Substances (EPS); polysaccharides, proteins, lipids, DNA
  • Frequently include other microbes - archaea, protozoa, fungi, microalgae
  • Biofilms are important factor in many benthic environments

  
• Bacteria - commensal / symbiotic behaviour


  Many bacteria live in/on animals, algae and plants

  Vital to digestion in many species:

  • Can influence feeding behaviours, including responses pre- and post- ingestion
  • There are as many bacterial cells in/on your body as there are human cells to make it (~0.2 kg)

  Responsible for most animal bioluminescence - luciferins are an EPS, evolved to 'pay the rent' to their animal hosts

  Mitochondria possibly evolved from symbiotic bacteria in early multicellular life - share many characteristics with bacteria
• Bacteria - endospores


  A few bacteria produce endospores:

  • Reduced version of 'parent' cell, with no metabolism
  • Can survive for 10s of thousands of years
  • Require no nutrients and can survive extreme UV, hot and cold temperatures, and chemical disinfectants - can even survive in space
  • Take ~8 hours to form when conditions (lack of nutrients) warrant
  • Can travel thousands of km with dust
  • Favourable conditions (warm, nutrients) trigger digestion of spore coat and restarting metabolism
  • Reactivation can happen inside animal host, leading to disease
• Endospore formation

  
• Archaea


  Prokaryotic, similar to bacteria, share some traits with eukaryotes

  Key features of archaea:

  • No membrane bound organelles/nucleus
  • Asexual reproduction and horizontal gene-transfer
  • Circular chromosomes
  • Similar translation/transcription mechanisms to eukaryotes
  • Some genes/metabolic pathways similar to eukaryotes

  Unclear if archaea can produce Endospores - none are known to

  No known pathogenic species
• Differences between archaea, bacteria and eukaryota

  
• Archaea

  May represent ~20% of microbial marine life

  Very wide range of energy sources - first to be detected are extremophiles:

  • Name comes from assumption that metabolism reflected ancient Earths atmosphere - believed to be type of 'living fossil'

  They are ubiquitous, including in the human alimentary canal

  Ecologically similar to bacteria, with a few differences: more vulnerable to viruses in marine systems
• Difference between Bacteria and Archaea

  
• Fungi


  Eukaryotic and heterotrophic - often saprophytic

  Very little known about marine fungi - only ~2,000 species described

  • Very difficult to isolate fungal DNA from other eukaryotic material
  • Most marine fungi cannot be cultured ex-situ

  Seem to be ubiquitous - found in all habitats; commensal, symbiotic, and pathogenic species better studied than free-living forms
• Fungi - morphology


  Many different phyla, like animals - massively variable morphology. Most of the organism is in the hyphal mass - the mycelium

  Mycelia formed by one individual can reproduce asexually; multiple individuals can form mycelia together for sexual reproduction:

  • Reproduction is highly complex - multiple sexes; varies between groups

  Fruiting bodies form and release spores

  
• Marine fungi - habitats and ecology


  Marine sediments and in substrates (in biofilms)

  Pathogens and saprophytes of phytoplankton - major components of flocculates (flocs - marine snow): the 'mycoloop' crucial bridge between inedible phytoplankton and zooplankton

  Pathogens of a wide range of plants, algae, and animals

  Intertidal environments

  • Transitional zones like mangroves and sand dunes - saprophytic, feed on decaying plant matter
  • Symbiotically as lichens
• Fungi - Lichens


  Symbiotic colony of multiple fungi and an algal species (green or cyanobacteria)

  Mycelium differentiated between the:

  • Upper and lower cortexes
  • 'Medulla' in the middle
  • Anchoring hyphae

  Essentially a self-contained ecosystem

  Grow where most spp. cannot - extreme physiological resistance (although sensitive to changes - can be good bioindicators of atmosphere pollution)

  Very few natural predators, poor competitors with plants

  {If the algae can survive without the fungus, relationship is parasitic - algal cells often destroyed in nutrient exchange}
• Importance of microbes


  Nearly all marine photosynthesis is microbial (bacteria, algae)

  Nutrient cycling though the ‘Microbial loop’ (bacteria, archaea, fungi, forams) – carbon, nitrogen, phosphorus, and other nutrients vital to life are made liable

  Biofilms stabilise sediment (bacteria, archaea, fungi, forams, algae) – dramatically increase productivity

  Disease (bacteria, fungi, viruses)

  Bioremediation (bacteria, fungi)

  Food

  Habitat

  Pollutants – heavy metals, hydrocarbons, plastic
• Protozoa


  Means 'first animals' - used to be a taxonomic term, but now a used to describe single-celled heterotrophic protists

  • Algae are the photosynthetic side
  • Some mixotrophy

  Common in moist environments. Can be free-living, commensal, mutual, or parasitic

  Wide variety of motility and feeding strategies across the group:

  • Some have specific structures: e.g., flagella/cilia for moving; cytostome ['mouth'] for feeding. Others use pseudopodia and phagocytosis

  Asexual reproduction with horizontal gene transfer is common

  Include Plosmodium, paramecium amoeba, and foraminifera
• Protozoa - Foraminifera


  Generally 0.1-1 mm, ~10,000 spp.

  Characterised by test ['shell'], and a streaming granulated ectoplasm

  • Test usually chitin, sediment particles, calcium carbonate, or absent
  • Test full of apertures - cytoplasm extends beyond (becomes ectoplasm)
  • Deposit feeders; active predators of diatoms, other forams, small animals; some parasites
  • Some symbiotic, single-celled algae; kleptoparasites
  • Predominantly marine benthic: soft sediments; some hard substrata
  • Alternate between sexual/asexual reproduction ('haploid/diploid alternation')
  • Important food source for deposit feeders
• Protozoa - Foraminifera

  
• Protozoa - Foraminifera


  Calcite tests extremely abundant in the fossil record

  Species and mineral composition used in palaeoceanography and paleaoclimatology

  
• Viruses

  Protein capsid containing genetic material

  Most abundant biological entity in aquatic environments

  Status as a 'life form' unclear:

  • Possess genes and evolve through natural selection
  • No metabolism, cannot reproduce without a host - free-existing virus particles (virions) are inert

  "Virocell" model proposes infected cells are life forms, whilst virions are not

  • Somewhat analogous to bacterial spores (although not related)

  May have evolved from plasmids

  Kill ~20% of microbial life every day