Degradation of 2,4,6-tribromophenol by bacterial cells attached to chalk collected from a contaminated aquifer A. Nejidat, I. Saadi and Z. Ronen Department of Environmental Hydrology and Microbiology, Institute for Water Sciences and Technologies, The J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, Medreshet Ben Gurion, Israel 2003/0784: received 4 September 2003, revised 9 December 2003 and accepted 18 December 2003 ABSTRACT A. NEJIDAT, I. SAADI AND Z. RONEN. 2004. Aim: To investigate the factors governing the adhesion and activity of the 2,4,6-tribromophenol (TBP) degrading bacterium Achromobacter piechaudii TBPZ-N61 on chalk from a contaminated aquifer. Methods and Results: Adhesion kinetics of TBPZ-N61 to grey and white chalk from a polluted fractured chalk aquifer was tested in a batch system. Both grey and white chalk contain ca 80% CaCO 3 , while grey chalk contains more organic matter (2Æ4%) than the white chalk (0Æ3%) and also contains Dolmite and Clinoptilolite. Adhesion of the bacterial cells to the chalk particles (<0Æ2 mm) occurred rapidly (96% of the cells within 15 min). Langmuir- fitted adhesion isotherms suggest that cells in the stationary phase, which are more hydrophobic, adhere to both grey and white chalk more efficiently than cells in the logarithmic growth phase. Increasing the pH (from 6Æ7 to 8Æ1) caused a significant reduction in cell adhesion to the chalk. Activity of attached cells was evaluated in both batch and column experiments. Logarithmic cells adhering to white and grey chalk were more active in TBP degradation than cells in suspension. In column experiments, significant TBP degradation was retained up to 30 days after a single injection of TBPZ cells. Thereafter, activity was fully recovered by amendment of yeast extract. Chalk surfaces that were incubated in situ in contaminated groundwater for 20 days still allowed the adhesion and activity of TBPZ cells. Conclusions: Taken together, our results show that bacteria adhere efficiently to specific sites on the chalk surfaces, and that sustained bacterial activity of the attached cells can be achieved by adding a carbon source such as yeast extract which also overcome toxic constituents that may occur in some chalk types. Significance and Impact of the Study: Bioremediation of TBP-contaminated chalk aquifers is made possible by the injection of bacterial cultures. Keywords: Achromobacter, adhesion, fractured chalk, hydrophobicity, subsurface, tribromophenol degradation. INTRODUCTION As a result of increased anthropogenic activity in arid and semi-arid regions there is an urgent need to protect limited water resources from contamination. There is a worldwide tendency to move industries with potential environmental risks into arid regions and to locate hazardous waste treatment facilities on low permeable chalk formations. These are generally considered to form a natural geological barrier, protecting the local aquifers (Hughes et al. 1994). In the Negev desert, Israel, numerous chemical industrial sites and waste disposal sites have been sited on fractured chalk formations of Eocene age. These formations are associated with a variety of fracture systems that control the advective flow of groundwater and govern the transport of potential contaminants. Mass transfer of water and solutes from the fracture voids into and from the chalk matrix might impose a significant hydraulic effect on the migration of contaminants Correspondence to: Ali Nejidat, Department of Environmental Hydrology and Microbiology, Institute for Water Sciences and Technologies, The J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, 84990, Israel (e-mail: alineji@bgumail.bgu.ac.il). ª 2004 The Society for Applied Microbiology Journal of Applied Microbiology 2004, 96, 844–852 doi:10.1111/j.1365-2672.2004.02222.x