Correlating Biodegradation Kinetics of 2,4-Dichlorophenoxyacetic Acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic Acid (2,4,5-T) to the Dynamics of Microbial Communities Originating From Soil in Vietnam Contaminated With Herbicides

Abstract

We determined the degradation rates of the herbicides 2,4-D and 2,4,5-T by two different bacterial communities. One of these originated from soil heavily contaminated with herbicides from Bien Hoa airbase, the other from the same soil but amended with additional carbon and Gibbs energy sources. The community from the contaminated, but untreated, soil degraded both 2,4-D and 2,4,5-T within 5 days of cultivation. The one from the amended soil, however, hardly showed any degradation of the compounds throughout 23 days of cultivation. After refreshment of the medium and prolonged culturing, however, this community degraded both herbicides within 25 days with progressively increasing rates. nMDS analysis revealed a highly significant differentiation pattern of the two communities. Cultures inoculated with amended soil showed a significant increase of Bacillus and Paenibacillus upon prolonged exposure to the herbicides. The succession in the culture from untreated soil, on the other hand, was dominated by species from the Proteobacteria. We were able to isolate two of them and they were shown to be related to Bordetella petrii and Sphingomonas histidinilytica, successively. Subsequent PCR analyses of their DNA revealed the presence of key genes involved in the degradation of the herbicides. This study provides a more fundamental understanding of the biodegradation of 2,4-D and 2,4,5-T by displaying part of the bacterial community succession during their breakdown allowing a comprehensive view on potential key degraders.

Correlating biodegradation kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the dynamics of microbial communities originating from soil in Vietnam contaminated with herbicides and dioxins

“…All others with additional carbon and energy sources performed less well (the vanillin and salicylate cultures) or were unable to degrade 2,3,7,8-TCDD at all (cultures with the mixture of aromatic amino acids and the mixture of lactate and acetate). We have seen a similar phenomenon in a study on the degradation of the herbicides 2,4-D and 2,4,5-T, in which the best performance was attributed to bacterial communities relatively starved in amended, more easily degradable carbon and energy sources ( Nguyen et al, 2021b ). Perhaps also in this study, the degraders of xenobiotics are outcompeted by strains that happily grow on the amended sources and consume essential nutrients and vitamins required by the degraders.…”

“…We have seen a similar phenomenon in a study on the 10. 3389/fmicb.2022.923432 Frontiers in Microbiology 10 frontiersin.org degradation of the herbicides 2,4-D and 2,4,5-T, in which the best performance was attributed to bacterial communities relatively starved in amended, more easily degradable carbon and energy sources (Nguyen et al, 2021b). Perhaps also in this study, the degraders of xenobiotics are outcompeted by strains that happily grow on the amended sources and consume essential nutrients and vitamins required by the degraders.…”

“…Although there is no direct evidence for the involvement of Bordetella and Sphingomonas in the degradation of 2,3,7,8-TCDD, the fact that they are relatively dominant in these 2 types of culture makes it a likely assumption. It has been shown earlier that species from the genera Bordetella and Sphingomonas have the genes encoding the enzymes degrading 2,4-D and 2,4,5-T, and indeed use that potential to degrade these herbicides ( Nguyen et al, 2021a , b ). We suggest that the presence of the herbicides 2,4-D and 2,4,5-T in the soil has contributed to the bioremediation results.…”

“…The other five were biotreated for the same period each with a different design. We took soil samples at the start of bioremediation and after 6, 21, and 38 months for further studies ( Nguyen et al, 2021b ). Untreated soil T1 was sampled after 21 months for the culturing experiments described in this experiment.…”

“…For the taxonomic summaries of the bacterial communities at phylum and genus levels, the counts in the OTU table were converted to relative abundances. Analyses of (i) alpha diversity indices (species richness and Shannon index), of (ii) NMDS (PERMANOVA and dispersion) and of (iii) log2-fold changes in abundance of OTUs are described elsewhere ( Nguyen et al, 2021b ). Before the alpha-and beta-diversity analyses (including NMDS), the OTU table was standardized using the decostand function (method = “hellinger”; Steinert et al, 2017 , 2019 ; Helber et al, 2019 ) of the R package vegan v.2.5-6 ( Oksanen et al, 2016 ) in R v3.3.1 ( R Core Team, 2016 ).…”