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Microbial Biofilms: Microbial Bunkers For Human Benefit
#1
Biofilms are found abundantly in the nature on rocks, in industrial pipelines, in clinical appliances and also inside living organisms. Microbial biofilms have gained popularity due to the negative impacts caused for human health such as forming dental plaques, as food pathogens, colonization of implanted human organs etc. Bacterial species like Pseudomonas aeruginosa, E. coli and yeasts like Candida are involved in clinical biofilms. However, besides these negative issues, biotechnology has made it possible to use these microbial communities with special characteristics for human efficacy.

This micro level association can consist of bacteria, fungi, archea, protozoa and algae. Mostly, microorganisms are present as biofilms in the environment. For an instant, microbial biofilms in the soil induces plant growth and protects plants from soil borne pathogens. A single biofilm consist of different species of the different organisms which makes it an advanced form of microbial communities. Biofilms are difficult to eradicate using antibiotics and other antimicrobial agents including chlorine using the standard concentrations. Bacterial biofilms readily develop antibiotic resistance if higher doses are used. Recent research focuses on defining minimum biofilm eliminating concentration (MBEC) instead of minimum inhibitory concentration (MIC) for bacterial biofilms.

Formation of biofilms basically depends on the adherent properties of the microbial cells. First the individual cells adhere to a biotic or abiotic surface in a reversible manner which then attaches to the surface more firmly by cell surface structures such as pilli, fimbriae. Then the cells increase in number. In further development of the biofilm, the cells produce an extracellular matrix composed of polysaccharides, proteins which in turn defend the biofilm from external environmental stresses. The microbial cells in the biofilm have unique physiological properties when compared to individual planktonic cells of the same organism. This uniqueness also corresponds to the relative position of the cell in the biofilm. The cells at the surface of the biofilm are more metabolically active and larger in size. They continue to divide and develop the biofilm whereas the cells at the depth are in a likely dormant state which becomes active with the death of surface cells. In antimicrobial treatments, only the top cell layer is affected in this micro-niche. Communication between microbial cells takes place by quorum sensing & they may form channels which permits uptake of nutrients, water etc. Micro-environment in the biofilm is subjected to changes in pH, oxygen concentration depending on the macro-environment. In terms of metabolic rates, biofilms are far more advanced than individual cells and hence can be used efficiently.

Biofuel production has gained a considerable attention as a substitute to fossil fuel which in turn reduces greenhouse effect caused by burning of fossil fuels. Scientists are trying to produce ethanol with the help of microbial biofilms using cellulose in plants as the starting material. Microbes involved in decaying plant substances which can form biofilms are used for biofuel production. These microorganisms are capable of producing hydrolytic enzymes called cellulosomes. Microorganisms found in the biofilms used for biofilm production include bacteria like Cellulomonas and fungi like Aspergillus. Industrial biofuel production is not sufficiently cost effective due to the required pretreatments which convert the cellulose to simple sugars or organic acids which is then converted to ethanol by fermentation using fungi and bacteria. As the biofilm is immobilized into a solid surface the recovery of the product becomes efficient. With the use of biofilms; bioprocessing, delignification, saccharification, fermentation and separation is possible inside a single reactor which is advantageous over usual industrial methods.

Biofilters are another use of biofilm technology which is used to purify polluted air released from industries. In this, the exhaust air is passed through the biofilter before it’s released or reused. Generally under optimized conditions, a biofilter can reduce off odours in exhaust air due to Ammonia, Hydrogen sulfide etc. Moisture content in the growth medium and the retention time for exhaust air can be controlled to optimize the process. Biofilter media usually consist of wood chips and compost which supplies nutrients, energy and water to microorganisms. Porosity in the biofilter is also significant for the efficiency of the biofilter. By products of the biofilter includes Carbon dioxide, water, minerals and organic compounds which makes it ecofriendly.

Bacterial biofilms are the powerhouse of microbial fuel cells (MFC). Using biofilms in the fuel cells permits waste decomposition which is another advantage. Microbial fuel cells consist of an anode, a cathode, electrolyte solution and an external circuit. An electric current is generated as a result of microbial metabolic activities in the biofilm. Microbial energy production using organic waste results in production of Carbon dioxide and free electrons. This flow of electrons from the medium to anode and back to cathode generate an electric current. The biofilm matrix play an important role in electrical conductivity as it encloses micro scale conductive nanowires. Clostridium cellulolyticum and Geobacter sulferreducens are commonly used bacterial species in microbial fuel cells. A recent discovery states that a bacterium, Bacillus stratosphericus found in the atmosphere was able to produce electricity more efficiently in an artificially created biofilm for a microbial fuel cell. In waste water treatments, microalgae and bacteria are used in biofilms converting the organic waste into simple products.

In bioremediation, biofilms are used for degrading oil spills, detoxification and purification which minimize the complex processes of using chemical and physical methods. Microbes are capable of removing the contaminants present in very minute quantities such as heavy metals, chlorinated hydrocarbons and polyaromatic hydrocarbons.

Apart from these major applications, biofilms are used as models for studies on quorum sensing, genetic heterogeneity and physiological properties. Further studies are performed to understand the complex behavior of these microbial communities and to use them for human benefit. However, the complexity of the microorganisms in a biofilm in terms of metabolic diversity and species diversity has made it difficult to understand the principle pathways in biofilms.
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#2
Biofilms are places were microorganims are found in abundance. These are natural growth supporting sites. While in research and micro labs, various growth supporting culture media are prepared and used to enrich microorganims. Any microorganism needs growth medium to support their growth in vitro. Today there are many culture media available in market to grow wide variety of microbes. Here is overview of various types of media used to support microbial growth. There are mainly two types of growth media. One is cell culture. These are unique or specific cell types which are derived from various sources like plants or animals.
These cell cultures are used to grow bacteria, yeast and fungi. Out of many culture media, Nutrient broth is most common. These media are poured in Petri-plates which are also known as agar plates. While there are few very specific media used for growth of specific or defined microorganisms. These media is known as selective media. These media does not allow others to grow while favors the growth of selective microorganism under test.
Different organisms need different media. For example Microorganism named Fastidious needs specialized environmental for their growth due to their complex nutritional requirements. Another example is virus. They need host for their growth as they are intracellular obligatory parasite. They grow on cell culture may be of bacteria or animals.
Depending upon such requirements, type of growth media are classified as Nutrient media, Minimal media, Selective media, Differential media, Transport media, cryo based media (Required at very low temperature conditions e.g. like at minus 20 °C and above). Enriched media are used for propagation of organisms that is to grow organism under test luxuriously.
A blood agar plate contains blood and they support growth of specific organism and is used to detect infection. This way diagnosis of infectious agent is done and specified drugs or antibiotics are recommended for quicker relief or cure from diseases. Media are used to isolate, grow and store important microorganism.
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Microbial Biofilms: Microbial Bunkers For Human Benefit00