Potential Arsenate-Reducing Bacteria from the Laguna Madre Display Low Phenotype Variation, but Utilize a Range of Carbon Sources and Tolerate High Concentrations of As(V)

The Laguna Madre, a hyper-saline estuary, is impacted by several contaminants including arsenic. The objective of this research was to identify arsenate-tolerant bacteria from the lagoon and determine whether the bacteria may convert As(V) (arsenate) to As(III) (arsenite) by one of 2 genetic pathways (e.g., arr pathway or ars pathway). Sediment samples were collected from two sites, site Frank West and site ABC. Sediment was diluted and cultured on Marine Agar 2216 with 100 µM sodium arsenate (dibasic). Thirty-five pure cultures were isolated and challenged to grow on media with increased arsenate concentrations. Cultures were gram-stained, compared phenotypically with API 20E^® strips, assayed with EcoPlate™ microplates to test their ability to utilize different carbon sources, and analyzed for protein production under conditions of arsenate stress. Results showed that most cultures could tolerate arsenate higher than 15 mM; however, culture growth, colony color, and protein production typically decreased as arsenate concentration increased. Bacteria isolated from site ABC displayed less phenotype similarity compared to organisms from Frank West. Most Frank West isolates used more than 10 carbon sources and were better able to use certain substrates compared to ABC bacteria. DNA extracted from the isolates is being used in Polymerase Chain Reaction assays to assess whether the bacteria possess genes in the arr or ars pathways. This will enable us to determine which As(V)-reduction pathway may be common in the Laguna Madre. We conclude that the Laguna Madre is inhabited by an assortment of bacteria that are potentially important in arsenic biogeochemistry.