|GRANT, MICHAEL - Washington State University|
|TYMON, LYDIA - University Of Idaho|
|HELMS, GREGORY - Washington State University|
|KELLER, C. KENT - Washington State University|
|HARSH, JAMES - Washington State University|
Submitted to: Geobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2016
Publication Date: 11/9/2016
Citation: Grant, M.R., Tymon, L.S., Helms, G.L., Thomashow, L.S., Keller, C., Harsh, J.B. 2016. Biofilm adaptation to iron availability in the presence of biotite and consequences for chemical weathering. Geobiology. 14; issue:6, pages 588-598.
Interpretive Summary: Bacteria in nature typically live in protective biofilms that can differ considerably from harsher conditions in their surroundings. Bacterial biofilms formed on mineral surfaces are thought to participate in weathering, an important process through which the minerals are broken down, soil is formed, and nutrients are made available to plants, but their role is not well understood. In this study, bacteria called Pseudomonas putida were allowed to form biofilms on biotite, a mineral rich in iron, or on glass slides. The study showed that biofilms grown on biotite had more cells, greater mass, and retained more iron, magnesium and potassium than did biofilms grown on glass slides. In addition, biofilms grown on biotite without supplemental iron in the growth medium had almost twice as much polysaccharide, a complex sugar molecule capable of binding positively charged mineral molecules, as did biofilms grown on biotite in the presence of growth medium containing supplemental iron. The results indicate that the bacteria responded to iron deficiency in their growth medium by increasing polysaccharide production, which increased their ability to bind and store iron and other positively charged mineral molecules released due to biotite weathering.
Technical Abstract: Bacteria in nature often live within biofilms, exopolymeric matrices that provide a favorable environment that can differ markedly from their surroundings. Biofilms have been found growing on mineral surfaces and are expected to play a role in weathering those surfaces, but this role is not well understood. Here we examine biofilm development by Pseudomonas putida in media either deficient or sufficient in Fe during growth on biotite, an Fe rich mineral, and on glass. Our working hypothesis was that the bacteria would respond to Fe deficiency by enhancing biotite weathering, in part by increasing the relative amounts of polysaccharide and cation exchange sites in the biofilm matrix. Biofilms grown on biotite, as compared to those on glass, had significantly greater biofilm biomass, specific numbers of viable cells (SNVC), and biofilm cation concentrations of K, Mg, and Fe whether or not media were amended with Fe. Proton nuclear magnetic resonance (1H NMR) spectroscopy showed that in the Fe-deficient medium, the relative amount of polysaccharide nearly doubled relative to that in biofilms grown in medium amended with Fe. The results indicate that the bacteria responded to Fe deficiency by increasing polysaccharide production, which increased the acquisition and storage of Fe and other cations due to biotite weathering.