Genetic bioaugmentation as an effective method for in situ bioremediation

Plasmid-Mediated Bioaugmentation for the Bioremediation of Contaminated Soils

“…Genetic (plasmid-mediated) bioaugmentation is defined as a technology in which donor bacteria harboring self-transmissible catabolic plasmids are introduced into the soil matrix in order to enhance, by HGT, the potential and rate of contaminant degradation of existing bacterial populations ( Top et al, 2002 ; Ikuma and Gunsch, 2010 , 2012 ). Compared to cell bioaugmentation, plasmid-mediated bioaugmentation appears a priori a more effective strategy for the bioremediation of organic contaminants, as the bacteria that will eventually degrade the contaminants (i.e., bacteria with the recently acquired plasmids harboring the necessary catabolic genes) are expected to be adapted to live in the soil under remediation.…”

“…In rhizosphere microcosms, Mølbak et al (2007) found that the transfer of plasmid pWW0 from P. putida resulted in transconjugants belonging to Enterobacteria and Pseudomonas . This well-characterized self-transmissible catabolic plasmid, pWW0, was also used by Ikuma and Gunsch (2012) to assess its potential for bioaugmentation in toluene-contaminated soil slurry.…”

“…The success of both cell and plasmid-mediated bioaugmentation greatly depends on the environmental (abiotic and biotic) conditions present in the soil to be remediated ( Cho et al, 2000 ; Bento et al, 2005 ; Wolski et al, 2006 ). In fact, during plasmid-mediated bioaugmentation, environmental factors can play important roles in the (i) transfer efficiency of catabolic plasmids, (ii) expression of horizontally acquired genes and, finally, (iii) contaminant degradation activity ( Popa et al, 2011 ; Ikuma and Gunsch, 2012 ). In particular, several abiotic factors such as soil moisture, temperature and OM content are known to affect bioaugmentation efficiency ( Figure 1B ).…”

“…In any case, the level of selective pressure required to promote conjugal plasmid transfer depends on the specific contaminant and its concentration, as well as on the specific catabolic plasmid. In soil slurry, Ikuma and Gunsch (2012) observed that environmentally relevant concentrations of toluene might not exert enough pressure for transfer of plasmid TOL from P. putida BBC443 to Serratia marcescens and P. fluorescens cells. In their study on the degradation of 2,4-D, DiGiovanni et al (1996) observed that this contaminant originated the required selective pressure for conjugal transfer of the intended catabolic plasmids.…”

“…Many biotic factors can also affect the success of plasmid-mediated bioaugmentation. Some genetic differences, such as guanine-cytosine (G+C) content and phylogenetic relationship between donor and recipient strain, can negatively affect the expression of the catabolic phenotype following conjugal plasmid transfer, as described by Ikuma and Gunsch (2012) . Indeed, for plasmid-mediated bioaugmentation, biological differences between donor and recipient bacterial strains such as, for example, phylogenetic distance ( Popa et al, 2011 ) and plasmid host range ( De Gelder et al, 2005 ; Sorek et al, 2007 ), can play an important role.…”