Plasmid ecology of marine sediment microbial communities

Abstract

9It is well documented that bacteria can readily exchange genetic information under artificial conditions typically used in most laboratory studies as well as to some extent in nature. The three mechanisms by which such genetic exchange can occur are transformation, transduction and conjugation. Transformation is the uptake of free DNA into a cell from the surrounding environment, while bacterial viruses mediate the exchange of genetic material during transduction and conjugation involves the direct transfer of DNA during cell-to-cell contact. In most cases, plasmids mediate the transfer of DNA during conjugation events, although chromosomal transfer can also occur. This review will focus mainly on plasm ids and the role of conjugation in marine sediment microbial communities. Plasmids, although often dispensible, provide a unique plasticity to an individual host cell or to an entire microbial community 'genome'. Specifically, plasmid-encoded traits mobilized throughout microbial communities can provide a means of rapid adaptation to changing environmental conditions. Examples of such adaptation can be seen in the increased frequencies of catabolic plasmids and antibiotic and heavy metal resistance plasmids within microbial populations upon exposure to selective pressures. Presently, the view of plasmid diversity and horizontal transfer dynamics is predominantly based on broad-and narrow-host-range plasmids isolated from bacteria of clinical and animal origins. While the exchange of plasmids is most likely an important mechanism by which bacterial populations in clinical environments can evolve and adapt, there remains a general lack of information regarding the role of plasmid-mediated transfer in marine ecosystems and how indigenous plasmids impact the microbial community structure and function. The combined application of molecular biology and microbial ecology techniques is providing new approaches to address the ecological role of plasmids in marine environments.

Metal and antibiotic-resistance in psychrotrophic bacteria from Antarctic Marine waters

“…Ecological studies have reported that metal and antibiotic resistance is becoming a global phenomena, with the Antarctic waters not being exempted, as the frequency of occurrence of plasmid-borne bacteria was high in Antarctic bacteria (Kobori et al 1984). Plasmids are known to carry resistance to antibiotics and metals (Sobecky 1999;Rasmussen and Sorensen 1998;Smith et al 1993). Hence the possibility of Antarctic bacteria to harbor antibiotic/metal resistance traits via horizontal transformation can be anticipated.…”

Aeromonas and Pseudomonas: antibiotic and heavy metal resistance species from Iskenderun Bay, Turkey (northeast Mediterranean Sea)

“…Plasmids are known to carry resistance to antibiotics and heavy metals (Smith et al 1993;Sobecky 1999). Marine bacteria adsorb, accumulate and transform heavy metals in the most food chains (Chan and Dean 1988).…”

Prevalence of tetracycline resistance genes in Greek seawater habitats

“…Isolation of Tc R plasmids and further characterization showed that they belonged to IncP group. IncP plasmids are commonly observed in natural environments and have been isolated from marine habitats (Dahlberg et al, 1997;Sobecky, 1999;Smalla et al, 2000b). Additionally, the identification of plasmids which could not be allocated to known Inc groups is not unexpected.…”