INFLUENCE OF DIFFERENT CHEMICAL TREATMENTS ON TRANSPORT OF ALCALIGENES PARADOXUS IN POROUS-MEDIA

Seven chemicals, three buffers, and a salt solution known to affect ba cterial attachment were tested to quantify their abilities to enhance the penetration of Alcaligenes paradoxus in porous media. Chemical tre atments-included Tween 20 (a nonionic surfactant that affects hydropho bic interactions), sodium dodecyl sulfate (an anionic surfactant). EDT A (a cell membrane permeabilizer that removes outer membrane lipopolys accharides), sodium PPi (a surface charge modifier), sodium periodate (an oxidizer that cleaves surface polysaccharides), lysozyme (an enzym e that cleaves cell wall components), and proteinase K (a nonspecific protease that cleaves peptide bonds). Buffers included MOPS [3-(N-morp holino)propanesulfonic acid], Tris, phosphate, and an unbuffered solut ion containing only NaCl. Transport characteristics in the porous medi a were compared by using a sticking coefficient, alpha, defined as the rate at which particles stick to a grain of medium divided by the rat e at which they strike the grain. Tween 20 reduced alpha by 2.5 orders of magnitude, to alpha = 0.0016, and was the most effective chemical treatment for decreasing bacterial attachment to glass beads in buffer ed solutions. Similar reductions in alpha were achieved in unbuffered solutions by reducing the solution ionic strength to 0.01 mM, EDTA, pr otease, and other treatments designed to alter cell structures did not reduce alpha by more than an order of magnitude. The number of bacter ia retained by the porous media was decreased by treatments that made A. paradoxus more hydrophobic and less electrostatically charged, alth ough alpha was poorly correlated with electrophoretic mobility and hyd rophobicity index measurements at lower alpha values. Filtration model calculations indicate that alpha values of <0.01 are necessary to ach ieve bacterial transport over distances large enough to facilitate bio remediation of contaminated groundwater aquifers. Chemical treatments that reduce alpha from 0.61 (1 mM MOPS buffer; ionic strength, 70 mM) to 0.0016 would increase bacterial penetration from 0.16 to 60 m, with only a 2-log reduction in cell concentration under typical groundwate r and soil conditions (assuming a water velocity of 1 m day(-1) and an average soil grain diameter bf 500 mu m).