Transport of Spores

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

Transport of Spores

	Transport of Spores The low metabolic rates of spores mean that they do not require external nutrients and water to generate sufficient energy for maintenance over long periods. Spores are produced in very high numbers. For example, fungi produce in excess of 1012 spores/fruiting body/year. A large percent of Spores do not survive transport in the atmosphere. Some spores have extremely thick walls which protect them from severe dessication. Some spores are pigmented which adds protection from exposure to damaging UV radiation.
Their small size and low density permit them to remain airborne for long periods before they sediment from the atmosphere. Spores are relatively light, containing gas vacuoles and they are of various shapes. They are aerodynamically adapted for extended lateral travel through the atmosphere. The passive liberation of spores into the atmosphere with air currents is common among microbes that produce dry spores on lateral mycelia (actinomycetes and fungi). Some spores are transmitted upward from microbial fruiting bodies by convection currents (surfaces exposed to sunlight have high temperature than the surrounding/air and as they warm the air in contact with them, will set up convection currents which are of great importance in air movements).
The effect of wind is to produce turbulence around stationary objects, though almost all surfaces are surrounded by a layer of still air, the laminar boundary layer (LBL), caused by the friction between the air and the object It is essential for microbes to have some method of getting through this LBL if they are to land on or be dispersed from a surface. Others move laterally and vertically with the wind currents. The higher the wind speed and lower the humidity, the greater the movement of spores. Many plant pathogenic fungi spread from one plant to another by this mechanism.
Some spores ate liberated only where water droplets in the air collide with the spore bearing bodies. For example, raindrops may liberate spores to the atmosphere. Spores and even vegetative microbes often enter the atmosphere as aerosols (splash from falling rain drops, spray from breaking waves, water striking rocks, sneezing and coughing) are important in the dispersal of some pathogenic bacteria and animal viruses.
	In addition to the passive mechanisms that allow microbes to enter the atmosphere, there are some active mechanisms that discharge microbial spores into the atmosphere. In Pilobolus, the entire spore cluster is ejected when a vacuole in the sporangium base becomes turgid and thin and the air inside increases in osmotic pressure and then causes the structure to burst and the spores to be carried away in a jet of water to a distance of 1-2 m. In most Ascomycetes, ascospores are actively discharged.

Having become airborne, both spores and vegetative microbial cells face the problem of survival. Most organisms can survive a short passage (mm) through the atmosphere but relatively few survive long distance transport because dessication can cause microbes in the atmosphere to lose viability. During the day, microbes carried through the atmosphere on rafts such as soil particles or dust may be protected from the harmful effects of UV radiation.

Home | Site map | Submit Article | Directory | Search