Desiccation, microbial

Hot water-extractable C accounts for 1-5% of soil organic C (Leinweber et al. 1995 Sparling et al. 1998 Chan and Heenan 1999) and about 50% of this is thought to be present as carbohydrate (Haynes 2005). Because it is usually extracted from air-dried soils much of the pool originates from desiccated microbial cells but it also includes exocellular polysaccharides, root exudates, lysates and humic material (Redl et al. 1990 Leinweber et al. 1995 Sparling et al. 1998). Both hot water extractable C (Sparling et al. 1998 Chan and Heenan 1999) and hot water-extractable carbohydrate (Ball et al. 1996 Haynes and Beare 1997 Debrosz et al. 2002) have been used as indices of soil quality. 

Besides being desiccated and irradiated, microorganisms traveling in space will be exposed to space vacuum that can reach 10-14 pascal (a unit of pressure—100 Pa = 1 mbar).57 The result is extreme dehydration, and naked spores can survive for only days if exposed to space vacuum. Survival of spores is increased if they are associated with various chemicals such as sugars, or are embedded in salt crystals. Nicholson et al. (2000) discuss the various stresses that a microbial cell or spore would have to endure to survive interplanetary travel.58 They include the process that transports them out of Earth s atmosphere, such as volcanic eruptions and bolide impacts, long periods of transit in the cold of space, and atmospheric entry into a new planetary home. Spores have been shown to survive the shock conditions of a meteorite impact and the ultraviolet radiation and low temperature of space.59 It is clear that panspermia is possible and even probable if bacterial spores become embedded in rocks that are ejected from one planet and eventually enter the atmosphere of another. Bacterial... 

There are different types of microbial mats, based on colorless sulfur bacteria, purple sulfur bacteria, iron bacteria and cyanobacteria. The most studied mats are those represented by filamentous cyanobacteria. They are widely distributed in protected intertidal sand flats where periodic desiccation discourages colonization hy marine invertebrates. The characteristic, sharply defined, colored hands of such mats (green in the top, red or purple a few millimeters down and heneath this hlack) were recorded as early as the middle of the ninetieth century. Such shallow waters or intertidal mats have now been recorded in many places of the World. These mats are all ephemeral or seasonal, and only in some specific conditions of tropical and subtropical lagoons can they form permanently. 

Proteins are readily hydrolysed by microbial enzymes, and their preservation requires desiccation, freezing or pickling, to retard microbial action. The key degradation step is peptide-bond hydrolysis, which is temperature dependent. The more highly ordered and cross-linked proteins—such as keratin, fibrinogen (in silk and mollusc-shell matrix) and collagen (comprising... 

The ability of the stone-colonizing microflora to cover and even penetrate material surface layers by the excretion of organic extracellular polymeric substances (EPS) leads to the formation of complex slimes, or biofilms, in which the microbial cells are embedded. Phototrophic organisms usually initiate colonisation by establishing a visible, nutrient-rich biofilm on new stone from which they can penetrate the material below to seek protection from high light intensities or desiccation. Stone EPS trap aerosols, dust and nutrients, minerals,... 

The cuticular waxes of insect species may contain the following chemical classes hydrocarbons, fatty acids, alcohols, triacylglycerols and wax esters (Golgbiowski et al., 2011 Nelson Blomquist, 1995). The waxes of some species also contain aldehydes, ketones, esters and sterols. The wax compositions of insects can vary depending on stage, sex, age, and their position in the colony hierarchy. Cuticular waxes can also vary within species as a response to living conditions such as temperature, dryness and available food. The major function of insect waxes is protection against desiccation, but they also prevent microbial infections, affect the adsorption of chemicals and play a role in chemical communication... 

Surface waxes serve a number of functions usually associated with protection. In plants and insects they prevent desiccation and in birds they serve to waterproof feathers. While a few components present in surface lipids can prevent growth of pathogens, the total surface wax layer certainly functions to prevent microbial entry into the organism. Some surface lipids serve as chemical communicants such as the hydrocarbon sex attractants and kairomone of insects. Although internal waxes are infrequently found in Nature, where they do occur they act as energy storage (e.g. in jojoba seeds or marine organisms). For a fuller review of all aspects of natural waxes refer to Kolattukudy (1976). 

Hydrocarbons comprise a majority of the cuticular lipids while wax esters, sterol esters, alcohols and non-esterified fatty acids are also common components. In addition to preventing desiccation, insect waxes also function to prevent abrasion, to act as a barrier against microbial penetration to reduce the absorption of toxic environmental chemicals (including insecticides) and in some cases some components may act in chemical communication (Jackson and Blomquist, 1976). 

Biological samples such as microbial cultures must be obtained carefully using disposable plastic wires or picks, and smeared on the Curie-point substrate. If the sample is from a liquid culture, a small amount of liquid is applied directly to the substrate. In each case, the samples are dried by heating in an oven or by vacuum desiccation. The samples are loaded into the instrument sequentially and the pyrolysate is... 

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