Competitiveness, microbial

Fumaric, succinic, and malic acid could replace the petroleum-derived maleic anhydride. The market for maleic anhydride is huge, whereas the current market for fumaric acid is small owing to its price limitations. Once a competitive microbial production process for fumaric acid is established, its market will likely increase. 

The use of microbial 1-dehydrogenations is essential to the manufacture of corticosteroids, as chemical dehydrogenation processes are commercially non-competitive. 

Microbial kinetics can be quite complex. Multiple steady states are always possible, and oscillatory behavior is common, particularly when there are two or more microbial species in competition. The term chemostat can be quite misleading for a system that oscillates in the absence of a control system. 

Plant and microbial competition for iron involves very complex interactions that are influenced by a number of factors (Fig. 2). These include differences in the level of siderophore production by all of the competing microorganisms, the chciTiical stabilities of various siderophores and other chelators with iron, their... 

The morphological and physiological dissimilarities between mycorrhizal symbi-o.ses probably determine their success and their distinct patterns in different ecosystems (92). Nitrogen (N) available to both AM and ectomycorrhizal plants should not be regarded as a single pool open to free competition. Specialization of its acquisition and utilization in a given habitat is an important feature of plant and microbial community structure, while the fact that the ability to exploit its sources (and tho.se of other limited nutrients) is not the same in all species may result in niche differentiation (93). If habitat specialization is a reflection of differences between mycorrhizal types, ectomycorrhizal and AM species could cooccur because they exploit different niches in the. same ecosystem. 

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. 

U. Schenk, R. Manderschied, J. Hugen, and H.-J. Weigel, Effects of CO, enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover, J. Exp. Bot. 46 987 (1995). 

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