Microbial diversity : a consequence of the aquatic environment

• Main Author: Lawrence, Anne C.
• Published: University of Warwick 1978
• Subjects: 579; QR Microbiology
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537260

Although prosthecate bacteria have been observed in freshwater environments, questions concerning the function or survival value of these integral cellular extensions are unresolved. However, it is now becoming apparent that this group of microorganisms forms part of a highly speciallsed indigenous population. An electron microscope survey of the bacterial population from several oligotrophic water bodies has shown that Hyphomicrobiurn and Caulobacter species constitute up to 20% of such populations, the percentage being correlated with the nutrient status of the system. The multiappendaged genera, at best, approach 1% of the total microbial population. 'Enrichment' systems to which no nutrients have been added, select for the latter. Several isolates of multiappendaged bacteria have been obtained from such systems. Studies on one of these has shown that gross phenotypic variation can be brought about by varying the nutrient status of the culture medium. These studies have shown that the prosthecae can be induced or repressed by environmental stimull. This phenotypic variation consequently makes the estimation, simply on morphological grounds, of the incidence of multiappendaged bacteria in the environment difficult. It almost certainly leads to gross underestimates of numbers. Similarly, studies on Hyphomtcroblum have demonstrated that this prosthecate bacterbin not only exhibits differentiation which is obligate to the cell cycle, but is also capable of environmentally induced differentiation. These observations also highlight a fundamental split concerning prosthecal function: - (i) where prosthecal formation is obligate and intimately involved in the cell cycle. e.g. Caulobacter and Hyphomicroblum and (ii) where prosthecae are non-obligate and environmentally induced, e.g. the multiappendaged bacteria, Ancalomicrobium.