Microbial activity transformation

Microbial activity may produce reactive intermediates that undergo spontaneous chemical transformation to terminal metabolites. This is quite a frequent occurrence, and its diversity is illustrated by the following examples ... 

However, relatively few studies have included growing plants in their experimental systems. In order to mechanistically understand the effects of pine roots on microbial N transformations rates under conditions of N limitation, l-year-old pine seedlings were transplanted into Plexiglas microcosms (121) and grown for 10-12 months. Seedlings were labeled continuously for 5 days with ambient CO concentration (350 iL L ) with a specific activity of 15.8 MBq g C. Then, soils at 0-2 mm (operationally defined as rhizosphere soil) and >5 mm from surface of pine roots (bulk soil) of different morphology and functional type (coarse woody roots of >2 mm diameter fine roots of <2 mm diameter ... 

Bioremediation is not restricted only to biodegradable organic contaminants. New techniques are currently under development for the bioremediation of metal-contaminated sites. Microbial activity can alter the oxidation state of some elements, reducing or increasing their mobility, and this transformation can be used for remediation purposes. 

Although the investigations of both Raunkjaer et al. (1995) and Almeida (1999) showed that removal of COD — measured as a dissolved fraction — took place in aerobic sewers, a total COD removal was more difficult to identify. From a process point of view, it is clear that total COD is a parameter with fundamental limitations, because it does not reflect the transformation of dissolved organic fractions of substrates into particulate biomass. The dissolved organic fractions (i.e., VFAs and part of the carbohydrates and proteins) are, from an analytical point of view and under aerobic conditions, considered to be useful indicators of microbial activity and substrate removal in a sewer. The kinetics of the removal or transformations of these components can, however, not clearly be expressed. Removal of dissolved carbohydrates can be empirically described in terms of 1 -order kinetics, but a conceptual formulation of a theory of the microbial activity in a sewer in this way is not possible. The conclusion is that theoretical limitations and methodological problems are major obstacles for characterization of microbial processes in sewers based on bulk parameters like COD, even when these parameters are determined as specific chemical or physical fractions. 

Basically, a concept for microbial transformations in sewer networks should cover soluble and particulate components and relevant processes in the water phase, in the biofilm and in the sewer sediments. In addition, mass transfer between these phases and an air-water transfer of oxygen should be taken into account (Figures 1.3 and 5.2). Although only the aerobic microbial activity will be focused on in the concept presented in this chapter, anoxic and anaerobic processes should be considered possible extensions (cf. Chapter 6). 

The microbial activity of wastewater under anoxic conditions is lower compared with aerobic conditions (Abdul-Talib et al., 2001). This is important to consider, because a low nitrate uptake rate (NUR) compared with the oxygen uptake rate (OUR) in units of electron equivalents means a reduced transformation rate of the most biodegradable fractions of the organic matter. As mentioned under the point on injection of air, this may have implications in terms of treatment. Furthermore, a relatively low NUR value also has operational advantages because of a reduced demand for nitrate to suppress sulfide formation. 

A process of bacterial degradation of carbon compounds can be conceived essentially as a conversion from a C02-predominant to a CH4-predominant system (Stumm and Morgan, 1981). The production of organic methane by microbial activity is a typical example of such conversion. Organic matter is first transformed into organic acids, which are then decomposed into acetic acid, gaseous hydrogen, and CO2, and finally recombined as CH4 ... 

Some of the popularly used anti-inflammatory drugs, such as paracetamol, are not an NSAID but have analgesic/antipyretic properties. Paracetamol specifically has relatively weak anti-inflammatory activity. Once excreted, it gets reactivated in the environment through some microbially mediated transformation (Henschel et al., 1997). The exact mechanisms by which paracetamol relieves pain are not very clear. It has a chemical structure that resembles several estronegic compounds. 

What is the influence of important environmental variables such as temperature, pH, light intensity, redox condition, ionic strength, presence of certain solutes, concentration and type of solids, microbial activity, and so forth, on the transformation behavior of a given compound ... 

It has become clear over the past ten years that the 1980s demonstration of anaerobic microbial dechlorination of PCBs is probably the most important discovery in the field of PCB biotransformations since Ahmed and Focht first demonstrated in 1973 that PCBs were biodegradable. Many new anaerobic microbial activities have been enriched and characterized from anaerobic fresh water and marine environments and heavily polluted industrial sediments. These anaerobic cultures are capable ofdechlorinating PCBs, thereby transforming highly chlorinated Aroclors to lower-chlorinated mixtures. This natural attenuation process is an important contributor to PCB degradation and detoxification in the environment and can form the basis for intrinsic remediation of many PCB-contaminated sites. 

The tests were conducted in an open, mixed and aerated reactor to maintain constant values of pH, DO, and temperature. Thus the difference in COD drop may not be related to pH, temperature. Aeration and mixing maintained DO around saturation in all tests, thus the effect of oxygen production at the anode is minimized. The only other process (other than microbial activity) that may relate to COD drop is abiotic transformation by electrolysis reactions at the electrodes. If abiotic redox of the organic content occurs in this study, then increasing the current density should increase the... 

Biological contamination of the sample can occur where sampling devices have not been sterilised. External bacterial contamination and microbial activity present in the sample could combine to degrade existing macromolecules. Chemical transformations such as methylation, cleavage of the carbon-metal bond, and reduction of the metal have occurred in the presence of micro-organisms (Thayer and Brinkman, 1984 Thayer, 1984 Krishnamurthy, 1992) as shown by the following equations ... 

Decho, A.W., and Hemdl, G.J. (1995) Microbial activities and the transformation of organic matter within mucilaginous material. Sci. Total Environ. 165, 33-42. 

In this chapter I describe how microbial activity may be estimated and what data are presently available on a) rates of microbial transformation and utilization, b) phenolic acid effects on soil and rhizosphere microbial populations, and c) the influences of soil and rhizosphere microbial populations on phenolic acid phytotoxicity. The resulting insight is then used to suggest a possible approach by which this hypothesis may be tested experimentally. 

Changes in microbial activity and thus, for example, phenolic acid transformation and/or utilization, can be monitored by changes in enzyme activity... 

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