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3 Cards in this Set
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Biofilms |
Microbes in aquatic environments attached to surfaces are members of complex, slime-encased communities called biofilms. Biofilms are ubiquitous in nature. They cause corrosion which result in economic losses. These biofilms often cause serious illness and failure of the medical device. Biofilms can form on virtually any surface, once it has been conditioned by proteins and other molecules present in the environment. Initially microbes attach to the conditioned surface but can readily detach. Eventually they form a slimy matrix made up of various polymers, called extra cellular polymeric substances (EPS). The EPS matrix allows the microbes to stick more stably to the surface. As the biofilm thickens and matures, the microbes reproduce and secrete additional polymers. A mature biofilm is a complex, dynamic community of microorganisms. It exhibits considerable heterogeneity due to differences in the metabolic activity of microbes at various locations within the biofilm. The waste products of one microbe may be the energy source for another microbe. The cells also use molecules to communicate with each other. DNA present in the EPS can be taken up by members of the biofilm community. Thus genes can be transferred from one cell to another. While in the biofilm, microbes are protected from numerous harmful agents such as UV light and antibiotics. The resistance of biofilm cells to antimicrobial agents has important consequences. When biofilms form on a medical device, treatment with antibiotics often fails, which can lead to serious systematic infections. The treatment failure is in part due to the presence of persisters in the biofilms. The persisters survive antibiotic treatment and then repopulate the biofilm once treatment ceases. Biofilm cells are regularly sloughed off, which may serve as a source of contamination. |
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Microbial Mats |
Microorganisms, through their metabolic activities, can create environmental gradients resulting in layered ecosystems. Microbial mats are multilayered structures of microorganisms, mainly bacteria, archaea, fungi and sometimes protozoans. They grow at interfaces between different types of material, mostly on moist surfaces, but some are found in dry environments. The colonized environments located in high altitude, they are common in the deep Biosphere, in subterranean environments with relatively low to high temperatures. Microbial mats are characterized by intensive internal carbon cycling. These highly striated communities of photoautotrophs and chemoheterotrophs develop in saline lakes, marine intertidal zones, and hot springs. Some cold seeps are the sites of microbial mats, which can sometimes cover several hundreds of meters. These mats are dominated by the giant, vacuolated sulphur-oxidising bacteria in the genera Beggiatoa and Thiomargarita. |
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Microbial loops |
Microorganisms play vital roles in the ecosystem as primary producers, decomposers, and primary consumers. All bacterial and archaeal cells are consumed by protists, which also consume other protists. These microbes are then consumed by herbivores that often select their food items by size, thereby ingesting both heterotrophic and autotrophic microbes. Thus nutrient cycling is a complex system driven in large part by microbes. The key to survival in the photic zone is the tight recycling of nutrients, rather than allowing them to sink to the seafloor. Within the microbial loop, photoautotrophic microbes are the primary procedures, and heterotrophic microbes consume dissolved organic matter (DOM) released as exudates by other microbes as well as larger plants and animals. Marine viruses are also a source of DOM as the lysis of their host cells contributes significantly to the return of nutrients into the microbial loop. This generates a common pool of DOM that serves as a nutrient source for all osmotrophic organisms. Protists including flagellates and ciliates, consume smaller microbes, which may include each other. Microbial cells, insoluble detritus, and other solid organic material are called particulate organic matter (POM). Because protists are then consumed by zooplankton, both DOM and POM are recycled at a number of trophic levels. The net effect of the microbial loop is the reuse of essential nutrients such as organic carbon, nitrate, and phosphate within the photic zone. Only a tiny fraction of the materiall sinks to the waters below, and resists degradation. |
