Microbial layer

Vertical distributions of dissolved Ba and total (dissolved+particulate) Pu, Am and Th in Framvaren Fjord all show increased concentrations with depth (Falkner etal., 1993 Roos etal., 1993). Ba cycling was dominated by its uptake into particulate matter associated with productivity in surface waters, followed by its regeneration at depth or in the sediments. Microbiological activity near the redox interface likely promotes the breakdown of settling particulate matter and the release of barite just above the 02/H2S interface (Falkner etal., 1993). Complex formation with dissolved organic carbon (DOC) is believed to be the main cause for the observed behavior of Pu, Am and Th (Roos etal., 1993). The distributions of these elements were not examined within the regions near the 02/H2S interface and the associated microbial layer. 

Potentiometric electrodes Ammonia or carbon dioxide gas sensing probes can be employed in the same way as the oxygen electrode, with the immobli-zed microbial layer held in place on the surface of the gas-permeable membrane. The ammonia probe is commonly used to determine amino acids by detection of ammonia production by microbial deamination of amino acids. Carbon dioxide probes are alternatives to oxygen electrodes for monitoring respiratory activity. 

Microbial layers (sludge) on metal surfaces can cause metal pitting or corrosion due to differing charge potentials between the covered and uncovered areas. Biopolymers in the biofilm trap ions creating a concentration of ions in the covered area. This will shift the potential of the metal surfaces to create localized corrosion cells. The area of lower concentration will be attacked. 

When we consider sources of methane we have to add old methane methane that was formed millions of years ago but became trapped beneath the earth s surface to the new methane just de scribed Firedamp an explosion hazard to miners oc curs in layers of coal and is mostly methane Petroleum deposits formed by microbial decomposi tion of plant material under anaerobic conditions are always accompanied by pockets of natural gas which IS mostly methane... 

Hospital steriliza tion is more limited in the availabiHty of steriliza tion methods and of packaging materials. Microbial invasion can occur particularly when articles are wrapped in traditional fabrics such as muslin (140-thread-count cotton). The expected shelf life of hospital-wrapped and sterilized articles is considered to be ca 21—30 days when a double-wrapping technique is used. Double-wrapping requires two successive wraps, each having a layer or layers of an approved packaging material. 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

A general relationship between the composition of the water and that of the soHd minerals with which the water has come into contact during infiltration and in the aquifer can be expected. Biological activity, especially in the organic layer above the mineral part, has a pronounced effect on the acquisition of solutes. Because of microbial respiration, the CO2 pressure is increased. CO2 pressure tends to increase the alkalinity and the concentration of and other solutes. 

Wastage is caused by biological material accumulating on or near surfaces. Microbial mats such as slime layers and massive accumulations of larger organisms cause most damage. 

Fig. 11.2. Antibiogram test diffusion of antibiotic on agar layer, preventing microbial growth.

The origin of the observed correlation was not established, and the relation was not interpreted as causal. It could be argued that a sustained elevated potential due to as-yet unknown microbial processes altered the passive film characteristics, as is known to occur for metals polarized at anodic potentials. If these conditions thickened the oxide film or decreased the dielectric constant to the point where passive film capacitance was on the order of double-layer capacitance (Cji), the series equivalent oxide would have begun to reflect the contribution from the oxide. In this scenario, decreased C would have appeared as a consequence of sustained elevated potential. 

Smith RV et al. (1975) Gas-liquid and thin-layer chromatographic determinations of xylenols in microbial extracts. J Chromatogr 106(l) 235-237... 

In the past, copper was believed to be toxic to most microbiological species. Although this may be true in a test tube under laboratory conditions, it is not generally true in the real world. In this real world, microbial communities excrete slime layers which tend to sequester the copper ions and prevent their contact with the actual microbial cells, Aus preventing the copper from killing the microbes. Many cases of MIC in copper and copper alloys have been documented, especially of heat-exchange tubes, potable water, and fire protection system piping. 

The rhizosphere lacks physically precise delimitation (18). The volume of rhizosphere depends on the rate of exudation and impact utilization of rhizodeposits (Chap. 6). The spatial and temporal distribution of exudates as well as their metabolism is related to the concentration of CO (Chap. 6). However, according to Darrah (Chap. 11), the layer of soil where microbial growth is affected by exudates can be 1-2 mm wide. 

The importance of including soil-based parameters in rhizosphere simulations has been emphasized (56). Scott et al. u.sed a time-dependent exudation boundary condition and a layer model to predict how introduced bacteria would colonize the root environment from a seed-based inoculum. They explicitly included pore size distribution and matric potential as determinants of microbial growth rate and diffusion potential. Their simulations showed that the total number of bacteria in the rhizosphere and their vertical colonization were sensitive to the matric potential of the soil. Soil structure and pore size distribution was also predicted to be a key determinant of the competitive success of a genetically modified microorganism introduced into soil (57). The Scott (56) model also demonstrated that the diffusive movement of root exudates was an important factor in determining microbial abundance. Results from models that ignore the spatial nature of the rhizosphere and treat exudate concentration as a spatially averaged parameter (14) should therefore be treated with some caution. 

Condensation will wash contaminating organisms onto the surface of the bulk phase where, especially if the vessel remains unstirred for some time, dilution of the surface layer, and hence the biocide in it, can allow profuse microbial growth to occur. When mixing recommences, such a high microbial loading will enter the bulk phase and may overwhelm a biocide. 

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