Chapter 8 



Maintaining Microbial Diversity 



HIGHLIGHTS 



Micro-organisms provide benefits and harbor danger. But safeguarding a diver- 

 sity of these organisms remains important, for few have been cataloged and 

 the potential contribution to agriculture, industry, and medicine is therefore 

 unknown. 



The most cost-effective way to preserve economically important micro-orga- 

 nisms today is through offsite collections. Micro-organisms that are isolated 

 and identified can be stored from a few days to as long as 30 years. 



Technologies used are freeze-drying (the most common method), ultra-freezing 

 (which costs more in labor and materials), immersion in mineral oil, low- 

 temperature freezing, and desiccation. The last three methods are suitable for 

 short-term storage only. 



A high priority in efforts to maintain a diversity of micro-organisms is the need 

 for an integrated database of current collections. Also needed is research on 

 microbial ecology, to better understand the extent to which plants and animals 

 depend on bacteria and fungi to survive. 



OVERVIEW 



Micro-organisms constitute a vast, though 

 largely unseen, part of the biotic world. Al- 

 though most frequently discussed in terms of 

 their harmful effects on humans, they are es- 

 sential to the proper functioning of ecosystems 

 as well as to the survival of many species of 

 plants and animals (19,25) (see box 8-A). The 

 public is less concerned, however, about po- 

 tential losses of microbial diversity than about 

 plant, animal, or ecosystem diversity (19). 



What Is Microbial Diversity? 



The wide range of micro-organisms not typi- 

 cally classed as plants or animals includes bac- 

 teria, cyanobacteria (blue-green algae), fungi (in- 

 cluding yeasts), protozoa, and viruses (see table 

 8-1). Although the microscopic, single-celled 

 bacteria are generally considered synonymous 

 with the term micro-organism, the field in- 



cludes such different things as the large ma- 

 rine algae of ocean kelp beds and the sub- 

 microscopic viruses that infect humans, 

 animals, plants, and other micro-organisms. 

 Even smaller than viruses are those infective 

 agents, such as viroids, that have been found 

 to be nothing more than pieces of genetic ma- 

 terial, lacking even the typical protein coats of 

 a virus. Thus, the diversity of micro-organisms 

 is immense, with only a relatively small frac- 

 tion of micro-organisms having been identified 

 (19,25). 



The concept of a species, borrowed from ani- 

 mal and plant biology, cannot be easily applied 

 to all micro-organisms (5,19,25,29). Research 

 frequently focuses on populations of microbial 

 cells that share common nutritional, chemical, 

 or biochemical characteristics. Such popula- 

 tions, each typically descended from a single 



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