Microbial breakdown products

The positive effects of humic substances often occur when the plants are grown in nutrient solution under anexic conditions in thin film isolators. This shows that the beneficial effects are due to the humic substances per se, rather than being mediated by microbial breakdown products. 

Of additional interest are recent epidemiological findings suggesting that persistent exposure during childhood to an environment which is rich in airborne microbial breakdown products such as lipopolysaccharides is associated with diminished risk for subsequent IgE-mediated disease [103, 104]. 

Neither methotrexate nor its microbial breakdown product, APA, is a substrate for xanthine oxidase [6, 215], although this may be more a function of the 2,4-diaminopteridine moiety, which itself is refractory to xanthine oxidase [204], rather than the glutamic acid residue. In fact, methotrexate is a potent competitive inhibitor of this enzyme, with a K value of around 25 fiM [218,219]. There is considerable controversy as to whether folic acid, a substituted 2-aminopteridin-4-one, is also an inhibitor of xanthine oxidase. It is not oxidized at carbon 7, unlike the parent compound, which is a poor substrate [204]. However, some workers have shown that folic acid is an extremely potent competitive inhibitor of xanthine oxidase, some 10-times more effective in vitro than allopurinol, whereas other reports claim that the inhibition is due to the contaminant 2-amino-4-oxopteridine-6-aldehyde (27), which is a photolytic breakdown product of folic acid [4, 171, 172, 218-220]. 

Utilization of phenolic acids by microbes can be substantial as long as conditions are appropriate, e.g., adequate nutrition, moisture, pH, and temperature. However, a variety of other factors can also influence microbial utilization of phenolic acids. For example, phenolic acid utilization by microbes was reduced when more readily available carbon sources were present in the soil such as glucose and phenylalanine (Fig. 2.24 Blum et al. 1993 Pue et al. 1995) or other sources of available carbon, i.e., roots (Blum et al. 1999a). The presence of methionine, however, did not influence the rate of phenolic acid utilization by soil microbes (Pue et al. 1995). Differential utilization of carbon sources by soil microbes is fairly common (Martin and Haider 1979 Harder and Dijkhuizen 1982 Papanastasiou 1982 Sugi and Schimel 1993). Thus the relationship between phenolic acid-utilizing microbes and their carbon environment is complex. There is yet another aspect that adds to this complexity. Initial microbial breakdown products of phenolic acids are frequently other phenolic acids. For example, ferulic acid is converted to caffeic acid or vanillic acid and these are converted to protocatechuic acid. Next the ring structure of the... 

Soil microorganisms produce many compounds that are potentially toxic to higher plants. Examples include members of the following antibiotics (1-6), fatty and phenolic acids (7-12), amino compounds (13-15), and trichothecenes (16, 17). "Soil sickness" and "replant problems" have been reported where certain crops or their residues interfere with establishment of a subsequent crop (18, 19). Toxins resulting from microbial activity sometimes are involved, but it is often unclear whether these are synthesized de novo in microbial metabolism or are breakdown products of the litter itself (20). 

Yemashova N, Kalyuzhnyi S (2006) Microbial conversion of selected azo dyes and their breakdown products. Water Sci Technol 53 163-171... 

The majority of microbial hydrogen production is driven by the anaerobic metabolism of pyruvate, formed during the catabolism of various substrates. The breakdown of pyruvate is catalyzed by one of two enzyme systems ... 

The concept of impedance microbiology is more than a century old however, it gained its popularity only in the mid-seventies. Impedance is based on the changes in conductance in a medium due to the microbial breakdown of inert substrates into electrically charged ionic compounds and acidic by-products. The detection time, that is, the time necessary for... 

More recently, the degradation of a-pinene by Pseudomonas jluorescens NCIMB 11671 was described [97,98]. A novel pathway for the microbial breakdown of a-pinene (119) was proposed, Fig. (23). The attack is initiated by enzymatic oxygenation of the 1,2-double bond to form the epoxide (127). This epoxide then undergoes rapid rearrangement to produce a novel diunsaturated aldehyde, occurring as two isomeric forms. The primary product of the reaction (Z)-2-methyl-5-isopropylhexa-2,5-dien-l-al (trivial name isonovalal) (128) can undergo chemical isomerisation to the -form (novalal) (129). Isonovalal, the native form of... 

Blum, U. Effects of microbial utilization of phenolic acids and their phenolic acid breakdown products on allelopathic interactions. J Chem Ecol 1998 24 685-708. 

Although the perfume oil is usually the first suspect whenever odor or color changes occur in a finished product, it is not always the culprit. Odor and color changes in the product base itself may occur due to oxidation, hydrolytic breakdown, complex formation, bacterial decomposition, or other causes. Sometimes the causes for instability are hard to track down, as in a case in the experience of one of the authors, where an off-odor in a cream was due to microbial breakdown that was made possible by absorption and inactivation of the preservative by the plastic container. It is always advisable to conduct a stability test of the unperfumed product along with the test of the perfumed product. 

Janse I, Van Rijssel M, Ottema A, Gottschal JC (1999) Microbial breakdown of Phaeocystis mucopolysaccharides. Limnol Oceanogr 44 1447-1457 Janse I, Zwart G, Maarel MJEC, Gottschal JC (2000) Composition of the bacterial community degrading Phaeocystis mucopolysaccharides in enrichment cultures. Aquat Microb Ecol 22 119-133 Joint I, Pomroy A (1993) Phytoplankton biomass and production in the southern North-Sea. Mar Ecol Prog Ser 99 169-182... 

Despite these obstacles, many signature molecules have been developed and utilized for the study of ancient samples (see Schopf and Klein, 1992). Of these molecules, perhaps the most interesting group recently utilized has been the methylhopanoids, breakdown products of 2-methyl-hopanepolyols, which are produced by cyanobacteria, and are common in microbial mats. The discovery of methylhopanoids in organic-rich sediments from 2.7 Ga (Brocks et al, 1999 Summons et al., 1999) provided the single best piece of evidence for the presence of cyanobacteria at this time. 

Avermectins and the breakdown products are nearly insoluble in water and bind strongly to soil. Thus they have little mobility and are unlikely to leach into groundwater. Avermectins are rapidly degraded in soil, sensitive to rapid photodegradation. When applied to the soil surface, its soil half-life was about 1 week. Under dark, aerobic conditions, the soil half-life is somewhat extended (2 weeks to 2 months). Microbial degradation also contributes to rapid loss from soils. Avermectins are also rapidly degraded in water (half-life 12-24 h), principally due to photodegradation. 

After death, cells self-destruct (the process of autolysis) under the influence of hydrolytic enzymes, which, in life, aided the recycling of cellular components. This process makes proteins and other components more readily available to the decomposers. Bacteria and fungi preferentially remove the more labile components from detritus and the residue becomes increasingly refract-ory. Much of the soluble product of the microbial breakdown of organic matter diffuses upward within pore waters to the sediment—water interface and is returned to the water column. Bacteria are important in all environments, but fungi are relatively... 

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