摘要:

In aerobic environments microorganisms are faced with a discrepancy of ~10 orders of magnitude between the available Fe (~10-17M) and their metabolic requirement for it (~10-7M). In contrast to facultative anaerobic environments, where dissimilatory iron-reducing bacteria (DIRB) are often abundant, few studies have detailed microbial interactions with Fe(III) (hydr)oxides in aerobic environments. To better understand acquisition of Fe from Fe(III) (hydr)oxides, we investigated the production of siderophore and Fe(III) reduction by a strict aerobe in the presence of synthetic hematite as a source of Fe. Pseudomonas mendocina grew best when Fewas supplied as FeEDTA (~1.8x108colony-forming units [CFU] ml-1), grew abundantly when Fe was supplied as hematite (~1.2x108CFU ml-1), and grew poorly when Fe was withheld from the medium (~5.5x107CFU ml-1). As expected, negligible siderophore was produced per cell when Fe was supplied as FeEDTA and more siderophore was produced in the hematite flasks than in the controls. Thus, growth of P. mendocina and the production of siderophore in the presence of hematite present compelling evidence that siderophore was produced as a mechanism to acquire Fe from hematite. For the Fe reduction experiments, Fe reduction by components of the supernatant fluid was induced weakly when Fe was supplied as hematite or as FeEDTA, but much more when the cells were cultured under extreme Fe deprivation. In fact, 16 times as much Fe reduction occurred in the controls as in the presence of either of the FeEDTA or hematite amendments. Our results, which contravene the long-held assumptions that Fe acquisition was facilitated solely by siderophores, provides a new perspective regarding microbial interactions with Fe bearing minerals.

ISSN:0149-0451    

DOI:10.1080/01490450050192965

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

We have used a relatively new microscopical technique, environmental scanning electron microscopy (ESEM), along with transmission electron microscopy (TEM) and light microscopy, to investigate a unique microbial community from a temperate-climate, cold sulfide spring near Ancaster, Ontario, Canada. ESEM allows the viewing of fully hydrated specimens that have not undergone the structural or chemical alterations imposed by the extensive procedures necessary for viewing biological specimens in a vacuum. Besides allowing visualization of microorganisms in their natural form and as intact assemblages, ESEM also detects elements, especially those lighter than Si, which tend to be lost or masked by the processes used to prepare samples for conventional SEM and for TEM thin sections. In this study we report new information about the structure of bacteriogenic sulfur deposits and their relationship to the structural aspects of a natural microbial community from a cold sulfide spring.

ISSN:0149-0451    

DOI:10.1080/01490450050192974

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Aquifer sediments from Norman, Oklahoma, were used to study the potential for microbial reduction of Cr(VI) to Cr(III). Black, clay-like sediments rapidly reduced Cr(VI) in both autoclaved and viable microcosms, indicating an abiotic mechanism. Lightcolored sandy sediments slowly reduced Cr(VI) only in viable microcosms, indicating a biological process. Cr(VI) reduction in these sediments had a pH optimum of 6.8 and temperature optima of 22°C and 50°C. Nearly complete inhibition of Cr(VI) reduction was observed when sandy sediments were shaken in the presence of oxygen. The addition of nitrate but not sulfate, selenate, or ferrous iron to sandy sediments inhibited Cr(VI) reduction. When electron acceptors were supplied in combinations with Cr(VI), reduction of Cr(VI) was greatest in the absence of nitrate. No loss of sulfate and no production of Fe(II) occurred in the presence of Cr(VI). The addition of molybdate to the microcosms did not affect Cr(VI) reduction in sandy sediments until very high concentrations (40 times the Cr[VI] concentration) were used. Interestingly, the addition of bromoethanesulfonic acid in amounts less than, or slightly greater than, the Cr(VI) concentration partially inhibited Cr(VI) reduction in sandy sediments. In the absence of this bacterial inhibitor, the sandy sediments produced methane. A methanogenic enrichment capable of reducing Cr(VI) during growth was obtained from sandy sediments. However, the enrichment produced methane only when Cr(VI) was absent, indicating that a shift in electron flow from methane production to Cr(VI) reduction may have occurred. These studies showed that Cr(VI) reduction in sandy aquifer sediments is a biologically mediated, anaerobic process that is inhibited by oxygen and partially inhibited by nitrate. The lack of sulfate reduction and sulfide production, as well as a lack of inhibition of Cr(VI) reduction by molybdate, argues against an indirect mechanism for Cr(VI) reduction, in which the sulfide produced during sulfate reduction would chemically reduce Cr(VI). Rather, Cr(VI) reduction may be mediated by a community of microorganisms that ordinarily use methanogenesis as the terminal electron-accepting process.

ISSN:0149-0451    

DOI:10.1080/01490450050193351

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Coprecipitation in carbonate minerals offers a means of slowing the transport of divalent radionuclides and contaminant metals (e.g.,90Sr2+, UO2+, Co2+) in the subsurface. It may be possible to accelerate this process by stimulating the native microbial community to generate chemical conditions favoring carbonate precipitation. In a preliminary evaluation of this approach, we investigated the ability of ureolytic subsurface bacteria to produce alkaline conditions conducive to calcium carbonate precipitation. Groundwater samples from the Eastern Snake River Plain (ESRP) aquifer in Idaho were screened for urea-hydrolyzing microorganisms; three isolates were selected for further evaluation. Analysis of 16S rRNA gene sequences indicated that two of the ESRP isolates were of the genus Pseudomonas , and the other was a Variovorax sp. The specific urease activities of the ESRP isolates appeared to be similar to each other but less than that of Bacillus pasteurii , a known urease-positive organism. However, calcium carbonate was rapidly precipitated in all cultures that were supplied with urea and calcium, and X-ray diffraction analyses indicated that calcite was always the predominant carbonate polymorph produced. The correspondence between measured calcium concentrations and equilibrium predictions suggested that the rate of calcite precipitation was directly linked to the rate of urea hydrolysis. These results are promising with respect to the potential utility of this approach for in situ remediation and indicate that further evaluation of this approach under conditions more closely simulating environmental conditions is warranted.

ISSN:0149-0451    

DOI:10.1080/782198884

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490450050193379

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor