Effect of root exudates and bacterial metabolic activity on conjugal gene transfer in the rhizosphere of a marsh plant

Abstract

Genetic exchange between bacteria in natural habitats is believed to be strongly influenced by availability of growth substrates and growth rate. To test this hypothesis, conjugal transfer of an RP4 derivative between Pseudomonas fluorescens and Serratia sp. was studied in a simple sand/plant microcosm and was related to availability of root exudates and bacterial metabolic activity. The presence of the plant (Echinochlora crusgalli) greatly stimulated transfer. Average transfer ratios (T/ DWR) were 8.9U10 3II in the rhizosphere and 5.5U10 3IS in sand unaffected by the plant root. The bacteria used root exudates as growth substrate and depending on cell density, the metabolic activity ([ Q H]leucine uptake) of the cells was higher in the rhizosphere than in the sand (around 1.0U10 3P and 0.5U10 3P fmol leucine CFU 3I h 3I , respectively). Thus, an apparent correlation between metabolic activity and transfer was observed. Additional experiments, however, suggested that there was no causal relationship between the two. When incubated in a sand microcosm containing root exudates, the metabolic activity of the bacteria increased while conjugal transfer ratios remained constant. Hence, contrary to the accepted view, root exudates and metabolic activity did not appear to be responsible for the stimulation of conjugal transfer in the rhizosphere. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.

Plant nodulation inducers enhance horizontal gene transfer of Azorhizobium caulinodans symbiosis island

“…In addition to its crucial role in the nodulation process, it was shown to stimulate wheat and Arabidopsis thaliana colonization by A. caulinodans (29,30). It was previously reported that opines produced by crown gall tumors initiated on plants by the pathogen Agrobacterium tumefaciens are required for Ti plasmid conjugal transfer among agrobacteria (31) and that root exudates enhance bacterial conjugal gene transfer in the rhizosphere (32,33). Our findings provide another example of the role of the host in the transfer of bacterial functions involved in interactions with eukaryotes, including bacteria-animal associations (34,35).…”

Gut and Root Microbiota Commonalities

“…In roots, root nodules, and guts, lateral transfer of genetic material between different bacteria has been evidenced (2,162,163), seemingly promoted by close contacts in high-density populations. The presence of similar catabolic or antibiotic resistance genes in various gut bacterial genera has been explained as acquisitions by lateral gene transfers (91).…”

Suppression of Soilborne Plant Pathogens through Community Evolution of Soil Microorganisms.

“…virulence, antibiotic resistance, etc.) has been demonstrated in roots 38) and leaves 50) of plants growing in controlled and field conditions. Finally, aggregation itself may promote the survival of bacteria by protecting the individual cells from various chemical and physical stresses.…”