Microbial Interactions in Soil PDF

11/23/2021 Microbial Interactions in Soil Ecological Interactions Between microorganisms in Soil Lec 3 1 Microbial Interactions in Soil Soil microorganisms perform a number of interactions during their presence in the soil that incl...

11/23/2021 Microbial Interactions in Soil Ecological Interactions Between microorganisms in Soil Lec 3 1 Microbial Interactions in Soil Soil microorganisms perform a number of interactions during their presence in the soil that include interaction with plant roots in the rhizosphere, interaction with soil constituents, interaction with other microbial communities that inhabit the rhizosphere Microbial interactions regularly improve the sustainable development of agroecosystem, plant growth, and health. 2 1  11/23/2021 The microbial community that existed in the rhizosphere is different forms that could be found in the bulk soil, as it was affected by root exudates that lead to high availability of nutrients and microbial biomass, which change the environmental conditions in the rhizosphere as a consequence of interactions between microorganisms microbial interactions with higher plants 3 Types of microbial interactions There are two types of microbial interactions that occurs in the rhizosphere: intraspecific interactions and interspecific interactions Intraspecific interactions occur between organisms of the similar species interspecific interactions occur between organisms of dissimilar species either two microbial populations or microbial population and plants or animals. 4 2  11/23/2021 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 5 Intraspecific interactions occur between organisms of the similar species 6 3  11/23/2021 Microbial Interactions Interspecific Interactions Intraspecific Interactions Positive Interactions Negative Interactions Cooperation Competition 7 Intraspecific Interactions It could be defined as interactions among individuals of single microbial population. This could be classified into two types: Positive Interaction Negative Interaction 8 4  11/23/2021 Positive Interaction (Cooperation) This type of interaction is called cooperation or intraspecific cooperation as it improves the growth of the microbial population 9 Types of Intraspecific Positive Interactions It appears in different types such as: 1) Prolonged lag phase  if small inoculum is used to avoid failure to grow (less than 10% inoculum used) 2) Motile bacteria remain in colonies during the growth  by making synchronized immigration (mass movement) to appear in the form of colony 3) Attaching of the cells to the matrix during biofilm formation 4) Cooperation of the cells in degrading insoluble substrates  such as lignin and cellulose by production of suitable enzymes 5) Genetic exchange between members of the same population through transformation, transduction, and conjugation to acquire resistance to different abiotic stress 10 5  11/23/2021 Negative Interaction (Competition) Is called: Intraspecific competition It occurs as a negative interaction between the individuals of the same population (competition within population). It is considered as a very important factor that regulates population size and density. Also it is responsible for the equal distribution of individuals within population in the ecosystem 11 cases of Intraspecific Negative Interactions It appears in different situation such as: 1) Low concentrations of available nutrients in natural habitats since all the cells use the same substrates and occupy the same ecological niche 2) Narrow available space 3) High microbial densities in natural habitat that lead to accumulation of some toxic products 12 6  11/23/2021 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 13 Interspecific Interactions It occurs among diverse microbial population that exhibit many different types of interactions. Positive interaction The interaction that leads to increase the growth rate Negative interaction The interaction that leads to decrease the growth rate Neutral Interactions (Neutralism) interactions that are unresponsive or neutral. 14 7  11/23/2021 15 Sym biosis together life Symbionts: the organisms involved Host: the larger organism, if there is one 16 8  11/23/2021 Symbiosis in Biology The term symbiosis is taken from the Greek sym which means “with” and biosis that means “living” at which is defined as “living together,” which is usually defined as long coexistence of two organisms. The term was first coined in 1879 by the German mycologist, Heinrich Anton de Bary, as “the living together of unlike organisms” He believed that this terminology should include parasitic, communalistic, and mutualistic relationships between different species of microorganisms. 17 This terminology faced a lot of confusion and variation for over 130 years since Anton de Bary (1879) coined the word. For example, some biologists believed that mutualism is considered common restrictive definition of symbiosis. Finally The definition of symbiosis to comprise the interactions at which no species is harmed (i.e., mutualism, commensalism, and neutralism) 18 9  11/23/2021 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 19 Neutral Interactions (Neutralism) It is a neutral association between dissimilar microorganisms inhabiting the same environment without impacting each other (the two members neither losing nor achieving anything from the relationship). Such association mostly is not a widespread form of interaction (it is rare) as it is always temporary since environmental conditions always change. This relationship occurs if the populations are living in culture with distinctive characteristics : such as: 20 10  11/23/2021 Neutral Interactions (Neutralism) 1. Separated by vast distance 2. Having dissimilar nutrient requirement 3. Living in Eutrophic lakes or marine habitats (!!!!!!!!!!) 4. Living in environment that does not authorize microbial growth like frozen products, polar ice, and frozen habitats 21 The difference between oligotrophic and eutrophic Oligotrophic are characterized by low nutrient values, which limits the lake's ability to support animal life. Oligotrophic Has low primary productivity, as a result of low nutrient content. These lakes have low microorganisms production, and consequently often have very clear waters, with high drinking- water quality. 22 11  11/23/2021 Eutrophic are characterized by: Excessive richness of nutrients (high nutrient values) in a lake, frequently due to run-off from the land high nutrient values, allows microorganisms and algae to grow in large numbers (dense growth ) which then allows animals that feed on those algae to also be supported 23 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 24 12  11/23/2021 Positive Interactions Such interactions consist of different relationships between different populations at which one population at least is benefited while the other is either benefited or not affected. 25 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 26 13  11/23/2021 1- Mutualism It is an obligatory or highly specific interaction between two populations in which both of them benefit from each other. It usually required close physical connection in which both partners may act as if they are one. When they exist separately, the physical tolerance and metabolic activities will be different for each single symbiont. Theoretically, mutualism could lead occasionally to the assembling of a new Species. 27 Types of Mutualism Mutualism could be classified into different types according to partner’s selection 28 14  11/23/2021 Types of Mutualism According to Interaction Patterns According to the partner’s selection, mutualism could occur in two forms: 1) Obligate Mutualism It occurs when both microorganisms live together very closely, and both species cannot survive without its mutualistic partner. 2) Facultative Mutualism It occurs when one of the two partners can survive without its mutualistic partner by itself in some conditions. 29 Examples of Mutualism 30 15  11/23/2021 Lichen The most common example for mutualism is the lichen, which is an association between fungus (ascomycetes) and algae (green algae) or cyanobacteria (blue green algae) Fungal partner surrounds the algal partner’s cells within fungal tissues that are exclusive to lichen associations. 31 Lichen Algae Fungi Mutualism Lichen 32 16  11/23/2021 2. Lichen Anatomy a. most of lichen body is fungal hyphae b. photosynthetic partner in a distinct layer c. sexual reproduction of fungal partner only d. asexual reproduction: soredia, fragmentation medulla 33 Lichens live in environments where neither fungi nor algae could live alone. While the fungi do not grow alone in the wild, some lichen algae occur as free-living organisms. If cultured separately, the fungi do not produce lichen compounds and the algae do not “leak” carbohydrate from their cells.. 34 17  11/23/2021 Although lichen association improves the range of ecological survival for both partners nonetheless this relationship is not always necessary for their growth and reproduction in natural environments especially algae since many of the algal symbionts can live independently 35 2- Commensalism It is a relationship at which one population benefits, while the other population is unaffected (neither harmed nor benefited). It is a very common relationship between different microbial populations. It is usually 1. unidirectional 2. not obligatory relationship 3. occurs when the unaffected population adapted the habitat in such a way that the other population benefits. 36 18  11/23/2021 Examples of Commensalism Type 1 During the modification of complex molecules by one population into other substrates in soil, the degraded products are regularly used by numerous other fungi and bacteria which cannot utilize complex molecules in the soil, like conversion of cellulose and lignin by fungi or bacteria through production of extracellular enzymes. This process improves 1. the nutritional properties of the soil 2. improve the activities of microbial communities in soil 3. improve plant growth and health. 37 Type 2 During the growth of facultative anaerobes and obligate anaerobes in the same site, the facultative anaerobes consume the oxygen from the environment which helps the obligate anaerobes to grow.  This process occurs commonly in soil 38 19  11/23/2021 3. Protocooperation (Synergism) Synergism (protocooperation) is a relationship that occurs between two or more populations at which both or all of them benefit. In this relationship microbial populations: perform a function which may not be performed individually produce a new product that neither each population can produce alone. This relationship is different from mutualism because it is not an obligatory interaction, none of the species depend on the relationship for existence, as each member can live and produce its own food individually. It is also called loose relationship since one member can be replaced by another microorganism 39 Examples of Protocooperation Examples 1 the relation between Thiobacillus spp. & Beijerinckia spp. (Thiobacillus spp. is an chemolithoautotrophic bacterium aerobic, acidophilic carbon dioxide fixer sulfur and iron oxidizer while Beijerinckia spp. is a heterotrophic bacterium aerobic nitrogen fixer slow grower 40 20  11/23/2021 These two organisms could be grown together since Thiobacillus spp. fix carbon dioxide for itself and Beijerinckia spp., While Beijerinckia spp. fix nitrogen to satisfy the need from nitrogenous compounds for itself and Thiobacillus spp. in medium devoid of carbon and nitrogen sources Also, the association of This relationship in the terrestrial ecosystem improves the carbon content in the soil nitrogen content in the soil mineral contents which in turn improve the growth and nutritional contents of plants in soil. 41 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 42 21  11/23/2021 3- Negative Interactions It consists of different relationships between different populations either two or more, at which one population at least is harmed while the other is either harmed, benefited, or not affected. 43 1- Ammensalism (Antagonism) It is the most common negative relationship in nature at which one microbial population suppresses or adversely influences the growth or the activities of the other population in the same environment by producing inhibitory substances either directly or indirectly. 44 22  11/23/2021 The population that produces the inhibitors is not affected by them and therefore gains the antagonistic edge. These inhibitors may be  antibiotics  toxins  organic acids  alcohols  lytic enzymes  harmful gases like  methane  ethylene  HCN  nitrite  sulfides or other volatile sulfur compounds. The population that adversely affects the other is called antagonistic species, and it constantly has great practical importance. 45 Examples of Antagonism Type 1 Bacillus subtilis, Pseudomonas fluorescens, and Streptomyces spp. Were described as producers of antibiotics (antibacterial or antifungal) that inhibit various pathogens and suppress different plant diseases like F. oxysporum Rhizoctonia solani Alternaria solani Pseudomonas solanacearum Alternaria brassicicola Penicillium digitatum Sclerotium sp. which are considered as fundamental agents of different plant diseases 46 23  11/23/2021 Type 2 In lichens, algae produce O2 which prevents the growth of anaerobic bacteria on it, while the fungi produce cyanide in concentrations toxic to other microorganisms. Type 3 Thiobacillus spp. reduces the soil pH to reach values as low as 2 through the oxidation of sulfide to sulfate. This low pH inhibits the growth of any pH-sensitive microorganism in soil. 47 2 - Parasitism It is a relationship between two dissimilar organisms that is called host parasite relationship in which one of them (parasite) lives in or on the other organism (host). The parasite lives in close contact with the host and forms metabolic association with the host and feeds on their cells, tissues, or fluids, while the host is badly affected. Sometimes the relation between the host and parasite could be turned from parasitic relationship to a pathogenic relationship. 48 24  11/23/2021 This relationship is widely spread in soil communities and characterized by its long period of contact the specialization between parasite and host. Also, parasite is usually smaller than the host (in most cases). 49 The important of this type of relationship This relationship has two sides, either useful or harmful. useful relationship If the parasitism is consummate on bacteria that are considered pathogenic to plants, it is considered as a useful relationship for plant growth and health. harmful relationship While if the parasitism is accomplished on bacteria that are considered profitable to plants, it is considered as a harmful relationship for plant growth and health. 50 25  11/23/2021 Example of Parasitism Viruses which attack bacteria (bacteriophages), fungi, algae, or plants are strict endoparasites (intracellular parasites) as they obligate parasite and cannot be cultivated on the media as free-living forms. 51 3- Predation Predation is the most dramatic relationship among microorganisms in nature, at which predator organism directly attacks a prey organism and feeds on it. This relationship has short duration, at which predators may or may not kill their prey prior to feeding on them But the normal result is generally absorption of the prey’s tissue through ingestion and subsequently the death of prey. Prey may be larger or smaller than predator. 52 26  11/23/2021 Important of Predation The predators have the capability to mineralize the organic compounds that are produced by microorganisms before it reaches the higher consumers; this process increases the rate of nutrient cycling returning the nutrients to the primary producers, stimulate their activities that leads to improve the nutritional content of the soil. Sometimes, the predators protect the environment from the prey by ingesting it, which is usually plant pathogen. 53 Examples of Predation The following predatory bacteria have been observed and characterized in soil: (a) Bdellovibrio bacteriovorus Is a predatory bacterium, which penetrates the cell wall and multiplies between the wall and the plasma membrane, which causes lysis of the prey and releases its progeny. It attacks and consumes different bacterial strains, including: Escherichia coli Salmonella typhimurium Helicobacter sp. 54 27  11/23/2021 4- Competition It is a relation that occurs between different populations in the soil which use the same limiting resources that are insufficient to support all the individuals. These resources include raw materials important for life such as water light nutrients oxygen space for occupying or any other resources, which is essential for survival and reproduction. 55 In this relation, the superior adapted microorganism will dominate and/or eliminate the others, which are depend on the same inadequate nutrient substances. Also, organisms which have the capability to grow faster are considered good competitors 56 28  11/23/2021 Types of Competition There are two ways in which microorganisms compete: 1- Resource Competition It occurs when the growth rates of both populations are limited by the same resource and one population has the ability to diminish the availability of that resource for the other populations. 2- Interference competition It occurs between two populations in which one of them damages the other population’s habitat either physically or chemically and excludes it from the habitation. 57 Microbial Interactions Interspecific Interactions Intraspecific Interactions Neutral Interactions Positive Interactions Negative Interactions Positive Interactions Negative Interactions Neutralism Mutualism Ammensalism Cooperation Competition Commensalism Parasitism Proto-cooperation Predation Competition 58 29  11/23/2021 Thanks 59 30