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Fundamental to the assessment of global microbial diversity is understanding the unit of measurement of diversity, namely the microbial species. Historically, definition of a microbial species has been accomplished by employing relatively crude methods based on laboratory culture. Limitations of both the methods and the philosophical construct underpinning the species definition for micro-organisms have been elaborately detailed by Woese (2004), who pointed out the fallacies of the ‘concept of a bacterium’ that led to the inclusion of all bacteria (as then understood) within the single grouping of ‘prokaryotes’, with a shared ‘prokaryotic’ organization evolved ultimately from a common prokaryotic ancestor (Stanier & van Niel, 1962; Stanier et al., 1957, 1963). Woese (2004) tracks the history of the ‘prokaryote–eukaryote’ dichotomy to the protozoologist Edouard Chatton (1938), whose reasoning was that, just as nucleated cells represented a monolithic grouping structurally and phylogenetically, non-nucleated cells (bacteria) also do so. Woese (2004) provides an eloquent explanation for the lack of philosophical understanding impelled by, on the one hand, technological advance and, on the other, ‘fundamentalist reductionism’ (the reductionism of 19th century classical physics), namely the view that living systems can be completely understood in terms of the properties of their constituent parts. The unfortunate aspect of fundamentalist reductionism is that it ignores the notion of emergent properties. The definition of a ‘micro-organism’ is, in itself, elusive.
Rita R. Colwell, Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 East Pratt Street, Baltimore, MD 21202,
Shah M. Faruque, International Centre for Diarrhoeal Disease, Bangladesh, Dhaka, Bangladesh,
G. Balakrish Nair, International Centre for Diarrhoeal Disease, Bangladesh, Dhaka, Bangladesh
Toxigenic strains of the Gram-negative bacterium Vibrio cholerae cause the most severe form of dehydrating diarrhea known as cholera and have been responsible for at least seven distinct pandemics of cholera (Faruque et al., 1998a). Since the first recorded pandemic, which began in 1817, V. cholerae strains associated with different pandemics are assumed to have undergone phenotypic and genetic changes with time. For example, although the seventh pandemic was caused by the El Tor biotype of V. cholerae, the sixth and possibly earlier pandemics were caused by the classical biotype. The genetic changes in V. cholerae associated with epidemics and pandemics, however, were not fully appreciated until the development and application of molecular techniques to analyze strains.
Recent application of molecular approaches has enabled extraordinary progress in our understanding of the evolution of V. cholerae. Like other bacteria, V. cholerae can be assumed to have existed well before human evolution and therefore to have originated primarily as a free-living aquatic microorganism. The fact that over a period of a million years some clones (serogroups) of this organism have acquired the ability to colonize transiently the human intestine and become an efficient human pathogen reflects the progressive acquisition of the genetic capability to become pathogenic for humans. They could have acquired this capability by embracing another “life style,” albeit accidentally, by carrying out a function in the human host that it performs either symbiotically or commensally for its nonhuman host but is, in effect, pathogenic to the human host, or alternatively, by finding a niche whereby the organism could amplify and perpetuate itself as effectively or more effectively, than it could in a free-living state.
The development and adoption of new agricultural technologies have made North American agricultural producers and processors among the most productive in the world. As a result, North American households spend a smaller percentage of their income on food than households in other countries. However, concern has been expressed about whether the record of increasing productivity gains in agriculture can be sustained. The mechanization of agriculture is now virtually complete, and the use of chemical inputs developed for agriculture following World War II is widespread. Fortunately, scientists agree that another major technological revolution has started – a biotechnology revolution. It is argued that biotechnology has the potential to allow some countries in Europe and the United States to increase their industrial and agricultural productivity and hence maintain their competitiveness in world markets.
Biotechnology has two characteristics that are significantly different from previous agricultural technologies. First, biotechnology can be used to enhance product quality by improving characteristics of plants or animals. Second, biotechnology has the potential for conserving natural resources and improving environmental quality by use of genetically engineered organisms for degradation of toxic chemicals in the environment and by the development of insect and disease resistant plant varieties.
Current status and prospects of agricultural biotechnology
Biotechnology has its roots in agriculture and presents important opportunities for mankind. Powerful tools have been created to carry out the purpose of agriculture, i.e. to use intelligently natural resources for the production of more and better food and fibre products. The tools of biotechnology differ from traditional methods primarily in their speed, precision and reliability.