Growth inhibition and stimulation of Shewanella oneidensis MR-1 by surfactants and calcium polysulfide.

Foam delivery technology (FDT) uses surfactant based foam to immobilize subsurface contaminants in situ. Where traditional approaches are impractical, FDT has the potential to overcome many of the technical challenges facing the remediation of contaminated deep vadose zone environments. However, little is known about the effects these reactive chemicals may have on microorganisms inhabiting the contaminated subsurface. In addition, there are currently no standard assays to assess microbial responses to subsurface remedial treatments while these agents are under development. The objective of this study was to develop a rapid laboratory assay to assess the potential growth inhibition and/or stimulation of microorganisms following exposure to candidate FDT components. Calcium polysulfide (CPS) and several surfactants (i.e. sodium laureth sulfate (SLES), sodium dodecyl sulfate (SDS), cocamidopropyl betaine (CAPB) and NINOL40-CO) have diverse chemistries and are candidate components of FDT. Shewanella oneidensis MR-1 cultures were exposed to a range of concentrations of these chemicals to determine the minimum bactericidal concentration (MBC) and the growth and viability potential of these components. Concentrations of SDS higher than 700 μM were toxic to S. oneidensis MR-1 growth over the course of four days of exposure. The relative acute toxicity order for these compounds was SDS > CPS > NINOL 40-CO>SLES≥CAPB. Dose dependent growth decreases (20-100mM) were observed in the CAPB and SLES treated cultures and both CPS and NINOL 40-CO were toxic at all concentrations tested (1.45-7.25 mM CPS). Both SLES (20-100mM) and SDS at lower concentrations (20-500 μM) were stimulatory to S. oneidensis MR-1 indicating a capacity to be used as a carbon source. These studies also identified potentially key component characteristics, such as precipitate formation and oxygen availability, which may prove valuable in assessing the response of subsurface microorganisms. This benchtop system provides a capability to assess adverse microbial-remediation responses and contributes to the development of in situ remedial chemistries before they are deployed in the field.