Microbial transformation of arsenic in Bengal floodplain

  • Hasina Afroz

Student thesis: Doctoral ThesisDoctor of Philosophy


Presence of arsenic in paddy soils in Bangladesh has become a major concern, with Holocene soils reported to have higher levels of arsenic compared to Pleistocene. However, to date there is limited data on how geomorphology, land use and soil microbes drive bioavailability of arsenic in the paddy soil in Bangladesh. In the present study, 16S rRNA amplicon sequencing and metagenomics (Illumina), alongside chemical analysis in paddy and nonpaddy soils, from Holocene and Pleistocene regions, of Bangladesh to investigate microbial composition and functional diversity of arsenic metabolism genes and how this may be related to differences in arsenic dynamics within these soils. Compared to Pleistocene soils, the Holocene soils had higher concentrations of arsenic, other elements and pore water arsenic species, the latter dominated by iAs. Further to that, paddy soils were shown to be elevated in arsenic and soil solution arsenic species compared to nonpaddy soils. Based on 16S rRNA amplicon sequencing and metagenomics the dominant bacterial phyla common to all soils were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi and Firmicutes but the overall diversity of bacteria was shown to be significantly higher in Holocene compared to Pleistocene soil. Metagenomics indicated that Geobacter, an anaerobic arsenic resistant organism, was most abundant in Holocene paddy soil. The functional genes related to arsenic reduction and resistance (arsC, araA/arsB, ACR3) were also shown to be most widely distributed in Holocene paddy soil. The anaerobic condition and higher level arsenic in the Holocene paddy soil may hence explain the increased abundance of Geobacter as well as of genes involved in arsenic reduction and resistance. The physiochemical properties of soil (pH and Eh) were the most dominant factors influencing arsenic speciation and microbial and functional gene abundance and diversity in paddy soil. The present study provides an insight into the microbial composition and functional gene diversity and their role in biogeochemical cycling of arsenic in paddy soil.
Date of AwardJul 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsCommonwealth Scholarship Commission in the UK
SupervisorCaroline Meharg (Supervisor) & Andy Meharg (Supervisor)


  • Arsenic
  • microbial transformation
  • paddy soil
  • arsenic methylation
  • arsenic reduction
  • holocene
  • pleistocene
  • arsM gene
  • arsC gene

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