Microbial extracellular enzymes

Microbial Extracellular Enzymes and Their Role in Dissolved Organic Matter Cycling... 

Hoppe, H.-G. 1991. Microbial extracellular enzyme activity A new key parameter in aquatic ecology. In Microbial Enzymes in Aquatic Environments. Springer-Verlag, Berlin. 

Munster, U., and H. De Haan. 1998. The role of microbial extracellular enzymes in the transformation of dissolved organic matter in humic waters. In Aquatic Humic Substances (D. O. Hessen and L. J. Tranvik, Eds.), pp. 199-257. Springer-Verlag, Berlin. 

Arnosti, C. (2003) Microbial extracellular enzymes and their role in dissolved organic matter cycling. In Aquatic Ecosystems Interactivity of Dissolved Organic Matter (Findlay, S.E.G, and Sinsabaugh, R.L., eds.), pp. 316-337, Academic Press, New York. 

All soil metabolic proce.sses are driven by enzymes. The main sources of enzymes in soil are roots, animals, and microorganisms the last are considered to be the most important (49). Once enzymes are produced and excreted from microbial cells or from root cells, they face harsh conditions most may be rapidly decomposed by organisms (50), part may be adsorbed onto soil organomineral colloids and possibly protected against microbial degradation (51), and a minor portion may stand active in soil solution (52). The fraction of extracellular enzyme activity of soil, which is not denaturated and/or inactivated through interactions with soil fabric (51), is called naturally stabilized or immobilized. Moreover, it has been hypothesized that immobilized enzymes have a peculiar behavior, for they might not require cofactors for their catalysis. 

It is a well-known fact that specific plastic materials like flexible PVC, Polyurethane or Silicone may be easily attacked by microorganisms leading to discoloration or mechanical failures.14 This susceptibility to microbial attack is mainly attributed to the plasticiser content of the material as well as other ingredients such as stabiliser or antioxidants.5,6 The predominant organisms on the surface of those plastics are fungi and actinomycetes and it is said that by the action of their extracellular enzymes other organisms such as bacteria may be able to grow on the material.7... 

Measurement of exoenzymatic activities is potentially useful in detecting the effects of toxicants on heterotrophic biofilm communities. Sensitivity and direct relationship with organic matter use and, therefore, microbial growth make extracellular enzyme activities a relevant tool to assess the toxicity of specific compounds. Use of novel approaches that combine enzymatic and microscopic tools (e.g. ELF-phosphatase) may be extremely useful to detect anomalies at the sub-cellular scale. 

The diversity of functions within a microbial population is important for the multiple functions of a soil. The functional diversity of microbial communities has been found to be very sensitive to environmental changes (Zak et al. 1994 Kandeler et al. 1996,1999). However, the methods used mainly indicate the potential in vitro functionality. Functional diversity of microbial populations in soil may be determined by either expression of different enzymes (carbon utilization patterns, extracellular enzyme patterns) or diversity of nucleic acids (mRNA, rRNA) within cells, the latter also reflecting the specific enzymatic processes operating in the cells. Indicators of functional diversity are also indicators of microbial activity and thereby integrate diversity and function. 

Abiontic, involving free extracellular enzymes or solubilizing agents, enzymes bound to soil surfaces, enzymes within dead or non-proliferating cells, or enzymes associated with dead cell fragments. Extracellular enzymes are important in the initial stages of organic matter oxidation, in which polysaccharides and proteins are hydrolysed to soluble compounds that can be absorbed by microbial cells and further oxidized in biotic processes. 

Component enzymes of the cellulase system have been purified from several microbial species (1-13), among which mutants of the imperfect fungus Trichoderma provide the highest levels of extracellular enzyme activity (14). From this organism have been purified / -glucosi-dases (EC 3.2.1.21), endo-l,4-/ -D-glucanases (EC 3.2.1.4) and 1,4-/ -d-... 

Chappell, K. R., and R. Goulder. 1995. A between-river comparison of extracellular-enzyme activity. Microbial Ecology 29 1-17. 

Even though substrate quality (i.e., chemical composition) is widely believed to be an important factor influencing microbial utilization of DOM, there are relatively few studies relating the composition and bioavailability of DOM. Sensitive assays for the measurement of the relative activities of various extracellular enzymes can provide an indication of the chemical composition of the bioreactive components of DOM (Sinsabaugh and Findlay, 1995 Findlay et al., 1998). The enzymatic potential of bacterial populations appears to respond fairly rapidly to seasonal changes in DOM composition in the Hudson River system. These observations clearly indicate that the chemical composition of DOM influences the microbial processing of DOM. 

The retention of DOM in microbial biofilms involves several processes (A) sorption of a DOM molecule to the biofilm, (B) diffusion into the biofilm, (C) cleavage by extracellular enzymes (in the case of high-molecular-weight organic matter), and (D) uptake and microbial utilization of the DOM molecule. 

C. Cleavage by Extracellular Enzymes and Microbial Uptake and Utilization... 

Vetter, Y. A., J. W. Deming, P. A. Jumars, and B. B. Krieger-Brockett. 1998. A predictive model of bacterial foraging by means of freely released extracellular enzymes. Microbial Ecology 36 75-92. 

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