Horizontal gene transfer of atrazine‐degrading genes (atz) from Agrobacterium tumefaciens St96‐4 pADP1::Tn5 to bacteria of maize‐cultivated soil

Abstract

The plasmid pADP1::Tn5 derived from pADP1[Atr+] carrying a Tn5 transposon conferring kanamycin and streptomycin resistances was constructed and introduced in Agrobacterium tumefaciens St96-4. This genetically modified strain was inoculated (approximately 10(8) cfu g(-1)) in potted soils planted with maize and treated or not with atrazine (1.5 mg kg(-1)). Bulk and maize rhizosphere soils were sampled 39 days after planting to look for soil indigenous bacteria that had acquired pADP1::Tn5. Four transconjugants were isolated from four different soil samples. The estimated transfer frequency of pADP1::Tn5 was 10(-4) per donor. Maize rhizosphere and atrazine treatment had no obvious effect on pADP1::Tn5 transfer frequency. The sequencing of the 16S rDNA sequences of the transconjugants revealed that they were almost identical and highly similar to that of Variovorax spp (97%). In addition, their characterization suggested that the atzA and atzB genes had been transferred from pADP1::Tn5 to the bacterial chromosome in two of the four transconjugants. These data suggest that the atz degrading genes are horizontally transferred in soil and possibly subjected to gene rearrangement.

New aspects on atrazine biodegradation

“…According to this, studies revealed that atzABC genes were widespread, having been detected in Canada, U.S.A., France, Croatia and China, and were also highly conserved (>97% similarity) indicating their recent dispersion within soil microflora (de Souza, 1998a;Rosseaux et al, 2001;Devers et al, 2004). Devers et al (2005) demonstrated that the atrazine-degrading plasmid ADP1::Tn5 was transferred from Agrobacterium tumefaciens St96-4 to soil microflora at a frequency of 10 -4 per donor cell. In two of the gram-negative transconjugants isolated, namely Variovorax sp.…”

Untitled

“…The presence of atrazine degradation genes on different size plasmids, suggests widespread of atrazine degradation genes among unrelated bacteria was not exclusively due to direct plasmid transfer. Furthermore, this view was further confirmed by the finding of bacteria with different combinations of atrazine degradation genes such as including trzN-atzBC, atzABC-trzD, and atzABCDEF (Devers et al, 2005). Atrazine catabolism initiated by triazine hydrolase TrzN, in a…”

Diversity of ‘benzenetriol dioxygenase’ involved in p-nitrophenol degradation in soil bacteria

“…This phenomenon could be explained on the basis of the fact that these functional genes have possibly undergone horizontal transfer from one organism to the other irrespective of their taxonomic ranks. It is well documented that horizontal gene transfer is responsible for diversity and distribution of catabolic gene(s) involved in the degradation of naphthalene, atrazine etc [27,28].…”