Microorganisms as hydrocarbon producers

Multifaceted and diverse energy sources will replace our once massive accumulations of energy reserves. One of these energy sources will be biomass and its natural products; in fact, it will most certainly be one of the essential elements in the complex of the future energy structure. Solar and chemical energy conversion, through biology as a practical energy conversion mechanism, has been extensively documented and reviewed; therefore, this discussion will be restricted to microbial fermentations with specific evaluations of the potentials for microorganisms to synthesize oily hydrocarbons as fermentation products. In biosynthesis, the acyclic hydrocarbons are referred to as fermentation products on the basis of the strict definition of fermentation as being those chemical energy yielding reactions that require organic components as electron acceptors. A generalized fermentation scheme is given in the figure. The scheme is purposely restrictive to emphasize products that are potential fuels. Each of the fermentation products represents a valuable energy form. The most efficient of these fermentation products, in terms of cost of production, cannot be fairly evaluated at this time because of the differences in cell cultivation requirements, product recovery, and most importantly, since many of these products via microbial fermentations are not yet sufficiently developed for commercial consideration. With increasing awareness of microorganisms which grow well or adapt to marginal, extreme or waste environments (taking into account the benefit value of these environments and the rising expenses of waste treatment) the distinct probability exists that the production costs in developing fermentation systems for fuel will become increasingly feasible and attractive. Although the compounds listed in the figure are acceptable fuels and are accessible through microbial processes, the obvious selection of a biochemical fuel for development cannot be determined at this time because not all systems have been adequately investigated. The competitive readiness of the different fermentation systems and the economics of producing each product as they become developed will automatically map out our course of action in years to come