Arsenate-respiring bacteria.

This chapter highlights the various approaches and techniques that others have used to investigate the geomicrobiology of arsenate respiration in subsurface and aqueous environments. This includes the discussion of classical microbiological techniques (e.g, enrichment culture and pure strain studies), environmental DNA methods, and culture-dependent microcosm studies. The overall goal is to provide investigators with a concise overview of the tools used to better understand the biological mechanisms influencing the arsenic geochemical cycle. To date most arsenate-respiring microbes have been isolated as heterotrophs. To investigate how iron influences the arsenic geochemical cycle, many studies have used synthetic hydrous ferric oxide (HFO) as an adsorbant for either As(V) or As(III). This HFO-As mineral is then used in batch or flowthrough experiments with iron and/or arsenate reducers to characterize how microbes affect the mineralogy and mobilization of arsenic. The results of any sediment microcosm study should be interpreted with caution, especially when extrapolating to generalizations about what occurs in the environment. Manipulation of oxygenation may also provide useful information regarding the types of respiration that contribute to arsenic transformations. The substrate in the column can be sampled at the end of an experiment and analyzed for mineralogical transformations, changes in cell densities and spatial variations, and also for molecular markers such as 16S rRNA gene if natural sediments are used.