Symbiosis and microbial interactions: mutualism,synergism,commensalism, competition, amensalism, parasitism, predation.
Symbiosis and microbial interactions
SYMBIOSIS (means “living together”) refers to relationships between organisms of different species (symbionts) that show an intimate association with each other.
- 1. Mutualism
- Extended synergism and an obligatory relationship in which both organisms benefit (+, +) and operate as a single organism.
v Microorganisms (Buchneria aphidocola; Rickettsia, Wolbachia pipientis) with insects.
v Flagellated protozoa with termite gut and wood roaches.
v Lichens (Fungi with Cyanobacteria)
v Zooxanthellae (spherical algal cells) with marine invertibrates (Sponges, Jellyfish, Sea anaemon, Ciliates, Hermatypic reef building corals).
v Tubeworm near hydrothermal vent (Red gutless tubeworm, Riftia spp.) with chemolithotrophic endosymbiont or Sulfur oxidizing bacteria.
v Clownfish gets protection, while the sea anemones become clean.
v Methanotrophs (methane fixing microorganisms) with methane vent mussels.
v Ruminants, herbivorous animals (Sheep, Cow) with anaerobic cellulolytic microorganisms.
v Flowers with their pollinators (Bees and humming birds gather nectar and spread pollen).
v Birds and mammals with the plants.
v Plants with microbes e.g. rhizobium in root nodules.
v Animals with other animals e.g. crocodile and plover bird.
- 2. Protocooperation/ Synergism
- Beneficial interaction of the same kind of organisms. The organisms, however, do not become dependent on one another (non obligatory; +, +).
- Association that involves the exchange of nutrients between two species is called as syntrophism or cross feeding.
v Nutritional protocooperation in microbial cultures: In a medium deficient in nicotinic acid and biotin, neither Proteus vulgaris nor Bacillus polymyxa will multiply as Proteus vulgaris requires nicotinic acid and Bacillus polymyxa requires biotin. In mixed culture, in the same medium. However, both grow since the partner bacterium synthesizes the missing vitamins.
v Desulfovibrio provides carbondioxide and hydrogen sulfide to Chromatium and gets sulphurdioxide and organic materials in turn.
v Nitrogen fixing microorganisms provides ammonium to cellulolytic organisms (Cellulomonas) and gets glucose in turn.
v Sulfide dependent autotrophic filamentous microorganism provides carbondioxide, organic material, and protection against toxic metals and thermal radiations to Heterotrophic organisms (polycheate worms, Silvenella, Ponpeii worm, Palm worm).
v Deep sea crustacean (Rimicaris exoculata shrimp) with filamentous sulphur oxidizing bacteria.
v Sulfide oxidizing bacteria (bacterial epigrowth) decreases toxic levels of sulfide for Nematodes Eubostrichus parasitiferus living in the interface of aerobic and anaerobic sulfide containing marine sediments.
v Microorganisms using hydrogen sulfide as electron donor and fix carbondioxide shows protocooperation with cave adapted invertebrates.
v Quorum sensing or autoinduction
v Mycorrhiza (Fungal association with roots of higher plants).
- 3. Commensalism
- One organism benefits (commensal) and the other (host) is neither harmed nor helped (+, 0).
v Barnacles have the benefit of moving through waters attached to the whale or shells.
v The clownfish lives in the tentacles of an anemone and is protected from potential predators.
v Some birds live with cattle to eat the insects present over them.
v Small mammals or birds lives in the holes in trees or orchids in rainforest Venezuela.
v Nitrogen cycle: waste product of one microorganism is the substrate for another. Nitrosomonas oxidises ammonia to nitrite which in turn is oxidized by Nitrobacter to form nitrate.
v Porcelain anemone crabs gets protection from their host anemones.
v A fermentative bacterium gets methane from anaerobic sludge digester methanogen.
v Methanospirillum, a fermentative bacterium gets hydrogen and carbondioxide from an anaerobic bacterium, Syntrophobacter.
v During milk spoilage, fermentative bacteria produce acidic waste products during fermentation, which is used by acid tolerant microorganisms present in the milk.
v During biofilms formation, initial colonizers make the environment suitable for the final colonizers.
v Soil microorganisms make the environment favorable for the growth of other microorganisms during various stages of degradation process of lignin in forest.
v The nonpathogenic strains of E.coli present in the intestine uses all the oxygen thereby modifying the environment making it more anaerobic, hence, suitable for obligatory anaerobic bacteroids to grow in the colon.
- 4. Competition (studied in detail by E.F.Gause; +, 0)
- Different organisms within a population try to acquire the same resource at the same time (a physical location or a limiting nutrient). Among the competing organisms, the dominating one will outgrow another, called as Competitive exclusion principle.
v In chemostats, competition for a limiting nutrient among microorganisms leads to exclusion of slower growing population under a set of particular condition.
v Among two competing ciliates for a resource, one is excluded.
v Organisms may develop differences in niches because of competition for resources.
- 5. Ammensalism (-, 0)
- A unidirectional process and a negative interaction in which one organism releases a specific compound that harms another organism.
v Antibiotics produced by one microorganism in low concentration can inhibit the growth of other susceptible organisms.
v Bacteriocin produced by one microorganism disrupts the cell wall of pathogenic microorganisms.
v Antibacterial peptides (cecropins in insects and defensins in mammals) released by the host in intestine is used to develop innate immunity.
v Acidic fermentation products inhibit the growth of other microbes by changing environmental pH.
v Attine ants are involved in a complex amensalistic process with bacteria and fungi.
v Potent lytic enzymes produced by Myxobacteria and Streptomyces digest the cell wall of other bacteria and destroy them
v Bt toxin inhibits insects.
v Human skin produces antimicrobial cathelicidin.
- 6. Predation
- Negative interaction where one organism (Predator) captures and consumes another (prey) (+,-).
v Bacteria (Bdellovibrio, Vampirococcus, and Daptobacter) penetrate the susceptible host or prey followed by its lysis.
v In sewage treatment, ciliates remove suspended bacteria be engulfing them.
v In marine environment, ingestion of nanoplanktons by zooplanktons provides a nutrient rich environment.
- In some cases, predation provides protection to the prey (+, +)
v Ciliates ingest Legionella and protect them from chlorine.
v Protozoa ingest Mycobacterium avium pathogen and control the disease.
v In microbial loop, the photosynthetic and chemotrophic bacteria mineralizes the organic matter thereby making it available for the primary producers.
- Parasitism (+, -)
- Negative interaction where one organism (parasite) is benefited from another (host) in terms of nutrition or physical maintenance.
v Lysogenic relationship between bacteriophage and the susceptible bacteria.
v Lichens (relation of fungi, mycobiont and algae, phycobiont) when both are nutritionally deprived.
v In biocontrol process, Rhizoctonia soloni and Mucor & Rhizopus.
v Ticks and fleas that live in a host animal’s fur bite the animal and drink its blood.
v mosquitoes feeding on a host
v Vines such as Kudzu growing on Trees
v Tomato Hornworm with Wasp Eggs
v Tapeworm or Hookworms living in Hosts Gut