Relationship Between Microbes and Atmosphere

Microbes and Atmosphere
Part-1
Relationship between Microbes and Atmosphere
Atmosphere as a Habitat
Transport of Spores
Sampling of Air
Launching
Transport of Microorgannisms in Air
Deposition and Adhesion
Types of Deposition
Gravitational Settling
Surface Impaction
Rain and Electrostatic Deposition
Methods of Air Sampling
Impingement
Impaction
Centrifugation
Filtration and Deposition
Sampling Methods and their characteristics

Relationship Between Microbes and Atmosphere

	Relationship between Microbes and Atmosphere The ecosphere or biosphere constitutes the totality of living organisms on earth and the abiotic surroundings they inhabit. It can be divided into atmo-, hydro- and litho-ecospheres to describe the portions of the global expanse inhabited by living things in air, water and soil environments, respectively. Microorganisms live within the habitats of these ecospheres. Each habitat has a set of physical, chemical, and biological parameters that determine the microbial populations that may thrive there. As a result of natural selection forces, characteristic communities develop within each habitat.
In some cases, particularly in extreme habitats such as salt lakes and thermal springs, the indigenous microbial populations exhibit adaptations to their physical and chemical surroundings that permit their survival. In other habitats, intense competition dictates which populations survive and become the autochthonous members of the communities living there. The vast majority of airborne pathogens are uniquely adapted for spreading in indoor environments.
The conditions of temperature, humidity and protection from sunlight and from oxidants which man controls for his own comfort serve also to protect pathogens during their exposed and vulnerable period when they transmit themselves from one person to the next. Most airborne pathogens die out rapidly in outdoor air but as individual species they depend entirely on man and his indoor environments for their propagation. The term 'air pollution' is therefore applied when there is an excessive concentration of foreign matter in the outdoor atmosphere which is harmful to man or his environment.
Air pollution is a growing menace to health throughout the world. The problem of air pollution was first brought to a sharp focus when air pollution epidemics took place in the developed countries during 1940s when some 4000 people died within 12 hours. These epidemics aroused public interest and stimulated the health authorities to take steps to ensure clean air. The different layers of the atmosphere are troposphere, stratosphere and ionosphere. Air is the simplest ecosystem since it consists of a single gaseous phase apart from condensed water vapour and dust. Atmosphere consists of 79% nitrogen, 21 % oxygen and 0.034% carbon dioxide. It is saturated with water vapour at varying degrees. For the most part, the chemical and physical parameters of the atmosphere do not favour microbial growth and survivial.
	Temperature decreases with increasing height in the troposphere (region nearest the earth’s surface interfaces with both hydrosphere and lithosphere). At the top of the troposphere, temperature is -43ºC to -83ºC which is below the minimal growth temperature for microbes. With increasing height in the atmosphere, the atmospheric pressure declines and concentration of available oxygen decreases to a point that prevents aerobic respiration. The concentration of organic carbon is low which is not sufficient enough to support heterotrophic growth; available water is scarce limiting even the possibility of autotrophic growth of microbes in the atmosphere. Microbes in the atmosphere are exposed to high intensity of UV radiation which increases with height as the atmosphere thins and offers less shielding from UV radiations and causes lethal mutations and death of microbes.

Stratosphere It contains a layer of high ozone concentration which absorbs the UV light protecting the earth's surface from excessive UV radiation. The stratosphere represents a barrier to the transport of living microbes to or from the troposphere. Organisms in this zone are thus transported slowly and are exposed for a prolonged period to the prevailing concentration of ozone and high UV light intensities. Only microbes shielded from these conditions in the stratosphere could survive passage out of earth's atmosphere.

Home | Site map | Submit Article | Directory | Search