Mobile genetic elements represent potential agents of change 

 and adaptation in ecological communities. Little is known about 

 the probability of interspecific and intraspecific gene transfer in 

 situ , and the resultant effects on communities. The tools of 

 molecular biology — such as PCR, cloning and sequencing, 

 hybridization technology, denaturing gradient gel electrophoresis - 

 - offer the ability to identify and quantify gene transfer in situ . 

 Combined with ecological investigations, these approaches may yield 

 an understanding of the contribution of gene transfer to fitness 

 (and niche) , community stability, and adaptation to stress or 

 change . 



In situ conjugal transfer of bacterial genes has been well 

 documented, for both aquatic and terrestrial ecosystems. This 

 mechanism of transfer is thought to be facilitated at interfaces, 

 e.g., in mat communities and in particulate consortia, where 

 conditions for cell to cell contact are optimal. The existence of 

 in situ transformation has long been suspected, but unequivocal 

 demonstration is much more problematic. Free DNA exists in 

 freshwater, marine, and terrestrial habitats, but its ultimate fate 

 (i.e., impact on the gene pool) is unknown. 



Recent observations revealed a high abundance of 

 bacteriophages in the marine pelagic environment. Potentially, 

 phages can mobilize bacterial genes by transduction, and so affect 

 bacterial activities. The use of molecular techniques makes the 

 estimation of the frequency of special types of phages and the 

 occurrence of transducing particles an approachable problem. 

 Moreover, specific probes can be developed to detect and enumerate 

 phage particles, even if a host cell is unidentified and there is 

 no way of propagating progeny phages. With such probes, the 

 dynamics of viruses in situ , and their temporal and seasonal 

 fluctuations, may be correlated with ecosystem biogeochemical 

 cycling and activities. 



Aquatic free phages are poorly defined, and no representative 

 has yet been cloned, purified, or characterized. Phages of 

 freshwater cyanobacteria and green algae are being intensively 

 investigated, and these studies can guide research on the marine 

 phages. Cloned and purified marine cyanobacterial phages can be 

 characterized by determining their morphology, DNA mass, and host 

 range. The replication of cyanobacterial phages closely resembles 

 that of E. coli phages except that the times of each developmental 



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