Mobilization of a recombinant nonconjugative plasmid at the interface between wastewater and the marine coastal environment

Abstract

The ability of aquatic bacteria isolated from habitats around the outlet of treated wastewater in a coastal marine ecosystem to mobilize the nonconjugative recombinant plasmid pCE328 was studied. A total of 208 strains were screened for their large plasmid content; 51 strains carried at least one large plasmid. Of these, 6 strains from wastewater and 8 from the marine environment were able to mobilize pCE328. Mobilizing strains were isolated from all habitats, and the majority belonged to the genus Aeromonas. The frequencies of mobilization in plate mating experiments ranged from 2 × 10−7 to 4.4 × 10−5 per donor at 15°C and 20°C. Mobilization occurred at lower frequencies in microcosm experiments. The results suggest that recombinant DNA released at such interfaces may be transferred rapidly to the autochtonous populations through several bacterial species.

Using microcosms to study gene transfer in aquatic habitats

“…Transfer frequencies, when quoted, can only indicate optimum transfer levels rather than serve as a realistic prediction of what will occur in nature. Many of the simple microcosms described do little more than replace laboratory media with a sterilized environmental sample [17, 21, 23–25, 30, 33, 35–37] and sometimes they even use a synthetic approximation [22, 29]. Nevertheless, when simple microcosms are designed to accommodate as many features of the environment as possible, some predictive information is obtainable, as illustrated by the beaker microcosm work of Bale et al [13–15].…”

“…Habitats investigated in this way (Table 1) include river water and epilithon [13, 14, 19–21], lake water [16, 17, 22], marine water and sediment [23–33], estuarine water and sediment [34], drinking water [35] and wastewater [36, 37]. A typical example is the beaker microcosm used by Bale et al [13–15] and Hill et al [20] to investigate gene transfer in river epilithon.…”

Extreme Environments and High-Level Bacterial Tellurite Resistance

“…Resistance determinants across phylogenetically-diverse taxa have a high degree of sequence similarity, suggesting they may be elements carried over from a common ancestor, evolved for survival in an ancient, metal-rich environment [115,116], or through lateral gene transfer [117]. Alternatively, metal resistance can be encoded for plasmids, which are capable of being mobilized and transferred, conferring resistance to previously-susceptible bacteria [118]. Different mechanisms have developed to deal with the presence of the highly-toxic oxyanion, tellurite, even within closely-related species of the same genus, as seen in Shewanella [119], but the strategies to confer high-level resistance are just beginning to emerge.…”