Precipitation of Barite by Myxococcus xanthus : Possible Implications for the Biogeochemical Cycle of Barium

Abstract

Bacterial precipitation of barite (BaSO 4 ) under laboratory conditions is reported for the first time. The bacterium Myxococcus xanthus was cultivated in a solid medium with a diluted solution of barium chloride. Crystallization occurred as a result of the presence of live bacteria and the bacterial metabolic activity. A phosphorous-rich amorphous phase preceded the more crystalline barite formation. These experiments may indicate the involvement of bacteria in the barium biogeochemical cycle, which is closely related to the carbon cycle.The mechanism by which barite precipitates in undersaturated seawater is one aspect of the Ba biogeochemical cycle that still remains unknown. Considerable research has focused on this element over the last 2 decades, since it is known to be a reliable indicator for variations in marine biological productivity (for examples, see references 3, 6, 9, 11, 16, and 17). Chow and Goldberg (5) first proposed that barite formation is biologically mediated; Bishop (3) and Dehairs et al. (6) provided evidence that such precipitation occurs in the upper water column in microenvironments of decaying organic matter and other biogenic remains. Morphologies and sizes of marine barite crystals in the water column and in marine sediments (for examples, see references 6 and 16) also indicate a possible biogenic origin. Barite precipitation by living organisms (protozoa) has been demonstrated in lacustrine freshwater environments (4,10,19). In marine environments, intracellular barite crystals have also been found in vacuoles of unicellular Exanthemachrysis gayraliae (12) and in Xenophyophorea (14). However, these organisms do not appear to account for the abundance of barite crystals in the water column, and the living organisms which directly precipitate barite have not yet been identified in seawater (1). Thus, a reasonable proposal would seem to be that bacteria play a role in this process. As an initial approach to the investigation of bacterial barite production, an experiment was performed using Myxococcus xanthus, an abundant and ubiquitous heterotrophic soil bacterium (8). This microorganism has been demonstrated to induce precipitation of sulfates, phosphates, and carbonates (reference 13 and references therein; 20). Although myxobacteria are recognized mainly as soil bacteria (8), they are also found in marine environments (15). Barite production under laboratory conditions. Living and dead M. xanthus cells (strain 422 provided by the Spanish TypeCulture Collection, Burjasot, Valencia, Spain) were inoculated on a solid culture medium with Ba (CM-Ba) (0.4% yeast extract, 2 mM BaCl 2 ⅐ 2H 2 O, 2% purified Difco agar-agar in distilled water [pH 7]). The inoculum was prepared by cultivating M. xanthus in liquid CT medium (7) for 72 h at 28°C with shaking (200 rpm) in order to obtain a density of ϳ2 ϫ 10 9 cells/ml. In living-cell experiments, 20-l aliquots of the M. xanthus inoculum were deposited on the solid medium. Dead cells were obtained by using heat (by autoclaving at 120°C for 20 ...

Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation

“…As noted above, the processes responsible for organic matter remineralization and BaSO 4 precipitation may be mechanistically coupled (e.g. González-Muñoz et al, 2003;Ganeshram et al, 2003). The northward flow of AABW at the base of the profile exhibits slightly higher Ba* than overlying waters, suggesting additional inputs of Ba -relative to Si -to this water mass as it travels through the southern loop of Antarctic circulation (Fig.…”

“…The formation of marine BaSO 4 appears to be critically dependent on the presence of heterotrophic bacteria, which play a key role in the degradation of POC in seawater (particulate organic carbon; e.g. Bertram and Cowen, 1997;González-Muñoz et al, 2003;Ganeshram et al, 2003;González-Muñoz et al, 2012). The majority of these heterotrophic microbes live within 100 m of the base of the euphotic zone where the supply of phytoplankton-derived organic matter is highest (e.g.…”

Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic

“…Several explanations have been proposed for the nutrient-like behaviour of Ba in seawater, though there is now considerable laboratory (Ganeshram et al, 2003;González-Munoz et al, 2003), field (Dehairs et al, 1980;Collier and Edmond, 1984), morphological (Bertram and Cowen, 1997), geochemical (Griffith and Paytan, 2012) and thermodynamic (Monnin et al, 1999) evidence to suggest that the formation of discrete, micron-sized barite (BaSO 4 ) crystals in the water column is a biological or biologically-mediated process, and that BaSO 4 is the major vector of particulate Ba in the modern water column. However, these observations do not address the mechanisms behind the similar depth profiles of [Ba] and Si(OH) 4 , which have been proposed to relate to the similar remineralisation depths of their respective carrier phases (BaSO 4 and opal, respectively; e.g.…”

Middle Miocene Global Change and Paleogeography of Panama

“…They have been attributed to precipitation from saline groundwater (Stoops and Zavaleta, 1978) and to local effects of acid-sulfate weathering (Carson et al, 1982). Intracellular, 1-4-ixm-diameter barite spherules and nodules are formed by many microbes (Hanoi;Gonzalez-Munoz et al, 2003): marine coccolithophorids (Exanthemachrysis), foraminifera (Hyperammina) and xenophyophores (Occultammina); soil and marine myxobacteria (Myxococcus); and fresh-water desmids (Closterium) and ciliophorans (Loxodes). These dustings in soils and within microorganisms are much smaller than the >1-cm-diameter barite nodules and sphemlites in paleosols of Panama and elsewhere (Table 5).…”