Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2023

Microbial biofilm, a study on phosphate solubilising bacteria during bioleaching of rare earth phosphate minerals (#205)

Arya van Alin 1 2 3 , Melissa K. Corbett 1 3 , Homayoun Fathollahzadeh 4 , M. Christian Tjiam 5 6 , William D. A. Rickard 7 , Xiao Sun 7 , Aaron Dodd 7 , Andrew Putnis 3 8 , Jacques Eksteen 4 9 , Anna H. Kaksonen 10 , Elizabeth Watkin 1 2 3
  1. Curtin Medical School , Curtin University, Perth, Western Australia, Australia
  2. Edith Cowan University, Joondalup, WA, Australia
  3. The Institute for Geoscience Research, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
  4. Curtin University, Perth, Western Australia, Australia
  5. Telethon Kids Institute, Perth, Western Australia, Australia
  6. The University of Western Australia, Perth, Western Australia, Australia
  7. John de Laeter Centre, Curtin University, Perth, Western Australia, Australia
  8. Institut für Mineralogie, University of Münster, Münster, Germany
  9. Western Australian School of Mines, Curtin University, Perth, Western Australia, Australia
  10. Land and Water, CSIRO, Perth, Western Australia, Australia

Australia is one of the main reserves of the rare earth elements (REEs) phosphate minerals, mainly monazite and xenotime. Phosphate Solubilising Bacteria (PSB) are capable of dissolving phosphate content of such minerals [1]. It has been demonstrated that REEs leaching efficiency is higher when microorganisms are in direct contact with the ore surface [2]. This study investigated the formation of biofilms by the PSB s Klebsiella aerogenes on the surface of monazite.

Initial attachment occurred during early hours (5-8) of exposure and was affected by extracellular DNA (eDNA) production, particle size, physico-chemical properties of the surface, total available area for attachment, and inoculation size. K. aerogenes produced eDNA which provides a high attachment-affinity toward the surface of P-RRE, hence, playing an important role during initial attachment. Attachment occurred preferentially on larger sized particles. Analysis of the dynamics of planktonic and sessile equilibrium during initial attachment revealed greater biofilm formation in the presence of monazite compared to a glass surface, in which lowering the initial cell concentration shifted the equilibrium toward a greater sessile population promoting biofilm formation, as did increasing the total available area.

A day after exposure, PSB colonise the surface of these minerals and form mature biofilms (second stage) which covered almost the whole surface. Microscopy analysis of the biofilm cross- sections showed a thin-layer structure. Biofilm selectively formed on and around physical imperfection but showed no selectivity toward particular mineralogy. On the other hand, eDNA production by K. aerogenes was impacted by the mineral source with higher levels produced when grown on monazite (light REEs) compared to a significantly lower level on heavy REEs containing xenotime.

Cross-section analysis of the immediate surface and subsurface of the bioleached mineral samples showed extensive erosion as K. aerogenes cells broke the ore surface into small particles. Elemental depth profiling showed a significant shift in chemical composition at the microbe-mineral interface and secondary-ion mass spectrometry revealed the first empirical evidence of the formation of REEs-organic acid complex formation.  

  1. Fathollahzadeh, H.; Eksteen, J.J.; Kaksonen, A.H.; Watkin, E.L.J. Role of microorganisms in bioleaching of rare earth elements from primary and secondary resources. Applied
  2. Fathollahzadeh, H.; Becker, T.; Eksteen, J.J.; Kaksonen, A.H.; Watkin, E.L.J. Microbial contact enhances bioleaching of rare earth elements. Bioresource Technology Reports 2018-a, 3, 102-108, doi:https://doi.org/10.1016/j.biteb.2018.07.004.