Microbe-Microbe-Interactions.docx

Microbe-Microbe Interactions Introduction Bacteria are rarely limited to a single type of interaction because their response is transient and influenced by chemical or physical environment. Cells are so small; hence, these are immediately influenced by their immediate environment. Microorganisms no...

Microbe-Microbe Interactions Introduction Bacteria are rarely limited to a single type of interaction because their response is transient and influenced by chemical or physical environment. Cells are so small; hence, these are immediately influenced by their immediate environment. Microorganisms not only respond to the chemical environment but also interact with other microorganisms in their immediate environment. Types of Interactions between Microorganisms and hosts Neutralism – no interaction, species A and B are not affected, even though they are growing in close proximity. Mutualism and symbiosis – interaction is needed to survive in the habitat, and specific species are required. Species A and B are both benefited. Protocooperation – Interaction is needed to survive in the habitat, but specific species are not required. Species A and B are both benefited. Synergism – Growth of one is improved by another. Species A and Species B benefit from each other. Commensalism – One benefits and the other is not harmed nor helped. The Species that is benefited is called Commensal (Species A), and Species B is the host, which is not affected, Competition – Organisms in the environment attempt to acquire limiting nutrient. Both of the Species is harmed. Parasitism and Predation – Host is usually compromised. Species A (parasite or predator) benefits, and Species B (Host) is harmed. Amensalism – the products of one impact another negatively. For instance, if Species A produces antibiotic, hence there is no effect on that species. Species B is harmed by the product. No interaction would be denoted by 0, Negative would be denoted by a negative sign. A positive effect is denoted by a positive sign. Neutralism Occurs when microorganism have no effect on each other despite their growth in fairly close contact. This is demonstrated in the lab using dual culture of bacteria, algae, or protozoa but is difficult to observe in nature. This is because the amount or population can be manipulated controlled in the lab. The culture density is low while the nutrient level is high. Each culture has distinct requirements for growth. For instance, some of the bacteria will be lipid metabolites, and algae will feed on other carbon sources. Commensalism The commensal benefits while the host is not harmed or helped. There is no requirement for a specific species because the response of bacterial cells to their chemical environment is transient and short-lived. When the commensal is separated from the host, it can grow on its own provided the physical and chemical requirements are favorable. Commensalism occurs when: Conversion of nonmetabolizable substrate by one species (Host) to a compound that is used by a second species (Commensal). One species (host) releasing vitamins, amino acids, and other growth factors, that are needed by a second species (commensal). One species (host) changing physiochemical environment which enables the second species to grow (commensal). Ways that the physicochemical environment can be changed is through: Destroying toxins. Changing the pH Removing molecular oxygen – molecular oxygen is not toxic by itself, but some bacteria have no enzymes to process the oxygen. Some oxygenic species are toxic to other microbes. Modifying osmotic pressure Endocommensalism - when bacteria grow inside the hosts. Many bacteria are growing in the intestine of animals and some of these do not benefit the host. For instance, some gut microbes in humans do not have apparent function in our gut. Bacteria growing within protozoan cells are also examples. Exocommensalism – Epiphytes: bacteria growing on surface of plants. Epizoites: protozoa growing on surface of aquatic animals. Examples: Cyanobacteria and algal cells secrete nutrients that attract bacteria to their surfaces. Competition Type of interaction when two or more species use the same nutrients or niches for growth. There is a limiting of growth of resources also apply to microbes. Law of the minimum Growth is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor). It was formulated by Justus von Liebeg. Law of Tolerance Organisms have an ecological maximum and minimum with a range in between which represents the “limits of tolerance” It was formulated by Ernest Shelford in 1911. Beyond the optimum range, while they can survive, reproduction is low, and mortality is high, compared to the optimum range. Competition results in exclusion of other species, which will result in a dominant species. Competition can also lead to the establishment of a steady state where multiple species coexist. Principle of Competitive Exclusion Two species or populations cannot inhabit the same niche: one will consistently out-compete the other. An experiment done by E.F. Gause in 1934 wherein he cocultured paramecium aurelia and paramecium caudatum. Grown separately, the paramecium is relatively similar. When co-cultured, Paramecium caudatum dwindled because paramecium aurelia has a higher growth rate. Extensive phototrophic activity results in cyanobacterial blooms. Chemolithotroph growth of aerobic hyperthermophilic bacterium Thermocrinis ruber in alkaline hotspring. Competitive Exclusion is a Major Bioprotective Mechanism of Lactobacilli against Fungal Spoilage in Fermented Milk Products The depletion of the essential trace element Mn by two Lactobacillus species was uncovered as the main mechanism for growth inhibition of dairy spoilage yeast and molds. As Mn increases, mold production increases. Mn is a limiting factor in the growth of mold production as lactobacillus culture obtain this first. Molds and yeasts cannot grow in plates with scarce amount of Mn. Steady state where multiple species coexist. Interpopulation competition: competition between same species. Intrapopulation competition: competition between members of the same population “Specialist” or “generalist” microbes are classified on the basis of nutritional capability. Limits the thriving of a “dominant species”. mixed population occurs. E.g.: gut. Generalist – whatever is available can be used for substrate. Specialist – they can have certain compound media wherein different nutritional requirements can be met. Parasitism Interaction that occurs when one species obtains nutrients from another for the purpose of cell growth. Viruses are obligate parasites. They attach specific cells by a process independent of an intermediate host. Highly specialized intracellular parasites that generally kill the host cell. Some viruses predate bacteria and may play an important role in shaping bacterial diversity. If the host of the virus is a bacteria, the virus is called a bacteriophage. “killing the winning population.” When bacteriophage prey on the bacterial species that are most abundant, which keeps the dominant population under control. This result to diversity. Lysogeny cycle of the virus replicating inside the host. When the provirus is carried on the chromosome of the host cell with no apparent harm to the host. Many bacteria harbor prophage (virus that infect and replicate only in bacterial cells). Lysogeny does not kill the host, only proliferates. Cell division incorporates the viral genome to the host genome. Induction (UV, harmful toxins, or chemicals), the cycle may shift to a lytic cycle wherein the genome is expelled to the host and replicate and forms daughter cells, lysing the cell and the host cell is killed. Predation Target other microorganisms for materials that enable the predator to survive. In microorganisms, the predator may be smaller than the prey. Obligate predator – cannot grow outside the prey. Facultative predator – also grow independently of the prey . Members of the predatory bacteria are known as “Bdellovibrio and like organisms” BALO/ These organisms are gram-negative that are motile by polar flagella. Can grow as: Epibiotic: grows on the surface of the cell. Periplasmic: between the plasma and outer membranes of Gram-negative bacteria. Cytoplasmic: grows in the cytoplasm of the prey. Life cycle of Bdellovibrio bacteriovorus. An attach phase cell is a motile, flagellated cell that moves toward the prey, possibly by chemotaxis. It attaches to a prey cell and enters the host periplasm by hydrolyzing the cell wall. Several host modification occur post-infection and the bdelloplast is formed. The Bdellovibrio feeds on degradation products of the host cell and undergoes chromosome duplication without cell division. Cell division follows. The attach phase cells mature by developing flagella. The host cells burst to release mature attack cells. Red dye: Bdellovibrio. The shape of the E. coli changes from rod to circular/spherical once infection. Facultative predator – bacteria that can grow with or without predation. Myxobacteria – fruiting body (myxospores) body bacteria. They aggregate by gliding motility. Formed with the spherical structure, they have filaments. Wolfpack feeding – they need a lot of their cells, because they cannot digest if they are individual cells. They need to be in groups for the frontal attack. Antagonism/Amensalism An ecological interaction between two species, wherein the association among organisms of two different species involves one that is destroyed or inhibited. And the other remains unaffected. Antibiotics – chemicals that inhibit growth of other microorganisms, but not themselves. May inhibit a metabolic step not found in the producer. E.g., the production of penicillin by fungi which inhibits cell wall found only in bacteria. Natural resistance to antibiotic produced by streptomyces spp. producing streptomycin. Bacteria and fungi developed mechanisms of antibiotic resistance. Limiting drug uptake - Modifying the cell wall structure by porin reduction in OM of G-. Biofilm formation which can be controlled through the use of bacteriophage, which can infect the host cell. Modifying drug target – bacteria can alter the number or structure of penicillin binding protein in the cell wall; therefore the antibiotics can’t enter the cell. This can also be done through ribosomal mutation (prevents the binding), methylation, or protection. Mutations in enzymes in metabolic pathways are also a method. Inactivating Drug – drug degradation, such as B-lactamase, which degrades the B-lactamase of the antibiotics, rendering the antibiotic useless. Transferring a chemical group to drug, such as through phosphorylation, changes the drug structure and inhibits binding to the enzymes or proteins of the cell. Activate drug efflux – pumps the drug out of the cell through the use of efflux pumps. Bacteriocins – antimicrobials produced by bacteria to inhibit the growth of similar or closely related bacterial strain. Generate holes in plasma membrane of susceptible bacteria. Pure bacteriocins also can be added to nonfermented food to promote the quality and safety of food products and inhibit pathogenic microorganisms. Listeria monocytogenes – psychrophile, grows in the cold and cause diseases in humans when they infect foods that are refrigerated. It can indirectly cause diseases. Hey can be controlled by the bacteriocin produced by the Lactobacillus plantarum. Bacteriocin is a viable alternative for antibiotics. Plantacyclin B21AG – bacteriocin produed by the lactobacillus species. Extracellular Enzymes – enzymes digest a suitable substrate even if the polymeric molecule is part of another microbial cell. Example: the lytic enzyme production of bacterial isolates from pepper against the fungal pathogen, Phytophthora capsica. Isolates that produce lytic enzymes, comparable to the positive control. Increasing the enzyme production for biological test control for fungal pathogen. Synthrophism Obligate mutualistic metabolism that occurs between two or more microorganisms where the metabolic end-product of the primary metabolizer is immediately consumed as substrate by the others. It is characterized by interspecies hydrogen transfer. Anaerobic environment. The complex organic compounds can be broken to simpler compounds through fermentation or hydrolysis, which can be further broken down to methane through methanogenesis, CO2 can be used as a source for methanotrophs. Iron reduction can use hydrogen from the fermentation and hydrolysis product as a substrate in an anerobic environment. Gibbs Free Energy – used to measure the maximum amount of work done in a thermodynamic system when the temperature and pressure are kept constant. ΔG – predict the direction of the chemical reaction . ΔG > 0 the reaction is non-spontaneous or endergonic. Reactants are retained. ΔG < 0 the reaction is spontaneous and exergonic. Products are formed. ΔG = 0 the reaction is at equilibrium. Through combined metabolic activity of microorganisms, endergonic reactions can become exergonic through the efficient removal of products and therefore enable a microbial community to survive with minimal energy resources. Strain S metabolizes ethanol and water to form acetate. It needs an input of 9.6kJ per mole of ethanol. Strain MoH uses hydrogen and carbon dioxide to produce methane and water, releasing energy, favouring the formation of the products. If they are co-cultured, they are b to combine the metabolic activity, making the endergonic reaction of strain S become exergonic. Ethanol plus carbon dioxide is able to create acetate , hydrogen, and methane. Total energy released is -112 kJ per mol of methane, resulting to the production of the products. Helps the production of strain S as it does not need energy whenever it metabolizes energy, Strain MoH uses hydrogen product of the strain S metabolization. Chlorochromatium aggregatum’: a phototrophic consortium formed by green sulfure bacteria epibiont (Chlorobium chlorochromatii) and a rod-shaped central bacterium Betaproteobacteria. GSB transfers organic compounds to central bacterium. Betaproteobacteria: provides the consortium taxis to light and sulfide is phototaxis. To the sulfide is chemotaxis. Co-culture of two hyperthermophilic arachea Pyrococcus furiosus (coccus) and Mathanopyris kandleri (rod), most likely based on H2 transfer. P. furiosus ferments organic compounds. M. kandleri performs methanogenesis. Mutualism and Symbiosis Consortium: group of diverse microorganism that have the ability to act together in a community. I.e., green sulfur bacteria. Root tip. Diatoms are unicellular algae with cell walls of silica fixation of CO2. Cyanobacteria have intracellular association with diatoms (cyanobionts) nitrogen fixers for diatoms. Extracellular disperse cyanobacteria in new environments. Lichen – symbiosis between fungi (mycobiont), cyanobacteria and/or algae (phycobiont). Classified based on the name of the fungi. Rhizines serve only to anchor to lichen to their substrate; they do not absorb nutrients as do plant roots. Upper cortex, medulla, lower cortex, rhizine: fungal structures. Algal zone: phycobiont. Hatena: eukaryote unicellular and alternates between autotroph and heterotroph. Host: Hatena Arenicola, heterotroph that feeds on algae using a complex feeding tube, unable to divide w/o a symbiont. Endosymbiont: algae, Nephroselmis becomes endosymbiotic chloroplast that replaces the feeding apparatus. Directs host towards optimum light intensity. Cell division, one cell retains chloroplast (autotroph), and the other is colorless (heterotroph). Symbiosis between bacteria and protozoa. Chlorella can provide foor for protozoa, protozoa can provide other nutrients, such as safety and a good environment for the bacteria to thrive. Fungus-Bacterium Symbiosis. Host: Rhizopus microsporus (funus) cannot produce spores without bacterium. Endosymbiont: Burkholderia produces seedling death to rice. TL;DR

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