Arsenic-Tolerant Streptomyces Isolated from a Hypersaline Estuary, the Laguna Madre, in Deep South Texas

Streptomyces are Gram-positive bacteria typically described in soils. They are known for producing secondary metabolites (e.g., antibiotics, pigments), they are used in biocontrol experiments against of fungal plant pathogens, and many Streptomyces display tolerance against soil contaminants. Less is known about marine Streptomyces, especially their tolerance toward toxins and their production of secondary metabolites. The research objective was to determine arsenic tolerance in Streptomyces from a hypersaline estuary mildly impacted with arsenic. Sediment Streptomyces were grown on Starch Casein Agar amended with 0.001 M sodium (meta) arsenite (AsIII) or sodium arsenate dibasic (AsV). Eight (8) isolates were evaluated for their ability to tolerate arsenic. Cultures were transferred weekly to fresh media and the concentration of arsenic was increased by 0.001M with every transfer. Isolated Streptomyces were also grown in liquid cultures amended with arsenic so that growth and protein production could be quantified. Most isolates tolerated arsenate up to 0.024 M when grown on solid agar media but did not grow well at arsenite concentrations above 0.001M. Cultures varied in pigment color; however, non-pigmented (white) isolates appeared equally tolerant toward arsenic as pigmented cultures. Growth and protein production in liquid cultures decreased as arsenic concentration, especially in cultures with arsenite. We conclude that marine Streptomyces are able to tolerate arsenate and arsenite. Organisms produce secondary metabolites (pigments) although the pigments do not seem to play a role in arsenic tolerance. The isolates will be tested for other secondary metabolites to determine whether they can inhibit the growth of other microorganisms.