A Halophilic Bacterium Inhabiting the Warm,CaCl2-Rich Brine of the Perennially Ice-Covered Lake Vanda,McMurdo Dry Valleys,Antarctica

Lake Vanda is a perennially ice-covered and stratified lake in the McMurdo Dry Valleys, Antarctica. The lake develops a distinct chemocline at about a 50-m depth, where the waters transition from cool, oxic, and fresh to warm, sulfidic, and hypersaline. The bottom water brine is unique, as the highly chaotropic salts CaCl₂ and MgCl₂ predominate, and CaCl₂ levels are the highest of those in any known microbial habitat. Enrichment techniques were used to isolate 15 strains of heterotrophic bacteria from the Lake Vanda brine. Despite direct supplementation of the brine samples with different organic substrates in primary enrichments, the same organism, a relative of the halophilic bacterium Halomonas (Gammaproteobacteria), was isolated from all depths sampled. The Lake Vanda (VAN) strains were obligate aerobes and showed broad pH, salinity, and temperature ranges for growth, consistent with the physicochemical properties of the brine. VAN strains were halophilic and quite CaCl₂ tolerant but did not require CaCl₂ for growth. The fact that only VAN strain-like organisms appeared in our enrichments hints that the highly chaotropic nature of the Lake Vanda brine may place unusual physiological constraints on the bacterial community that inhabits it.     

Multicopper oxidase involvement in both Mn(II) and Mn(III) oxidation during bacterial formation of MnO2

Global cycling of environmental manganese requires catalysis by bacteria and fungi for MnO₂ formation, since abiotic Mn(II) oxidation is slow under ambient conditions. Genetic evidence from several bacteria indicates that multicopper oxidases (MCOs) are required for MnO₂ formation. However, MCOs catalyze one-electron oxidations, whereas the conversion of Mn(II) to MnO₂ is a two-electron process. Trapping experiments with pyrophosphate (PP), a Mn(III) chelator, have demonstrated that Mn(III) is an intermediate in Mn(II) oxidation when mediated by exosporium from the Mn-oxidizing bacterium Bacillus SG-1. The reaction of Mn(II) depends on O₂ and is inhibited by azide, consistent with MCO catalysis. We show that the subsequent conversion of Mn(III) to MnO₂ also depends on O₂ and is inhibited by azide. Thus, both oxidation steps appear to be MCO-mediated, likely by the same enzyme, which is indicated by genetic evidence to be the MnxG gene product. We propose a model of how the manganese oxidase active site may be organized to couple successive electron transfers to the formation of polynuclear Mn(IV) complexes as precursors to MnO₂ formation.     

Chemical and microbiological studies of sulfide‐mediated manganese reduction 1

Laboratory studies of manganese reduction by naturally occurring reduced inorganic compounds were undertaken, both to study further possible in situ mechanisms of manganese reduction and to examine how manganese redox reactions might be coupled to other biogeochemical processes. Chemical manganese reduction by sulfide (in the presence of excess manganese oxide) was found to be rapid and complete, with all sulfide being oxidized within 5–10 min. The reduction of δMnO₂ by sulfide involves a two‐electron transfer, with S° the predominant oxidized sulfur product. Using a marine sulfate‐reducing bacterium (Desulfovibrio sp.), the kinetics of sulfide‐dependent, bacterially mediated manganese reduction were studied; the rate‐limiting step was bacterial sulfide production. These findings suggest that in stratified marine environments (such as the Black Sea, Saanich Inlet, or certain coastal sediments) manganese reduction should occur just below the oxic‐anoxic (O₂/H₂S) interface or redox boundary as a result of the chemical reaction between manganese oxides and sulfide produced by sulfate‐reducing bacteria.     

Three manganese oxide-rich marine sediments harbor similar communities of acetate-oxidizing manganese-reducing bacteria

Dissimilatory manganese reduction dominates anaerobic carbon oxidation in marine sediments with high manganese oxide concentrations, but the microorganisms responsible for this process are largely unknown. In this study, the acetate-utilizing manganese-reducing microbiota in geographically well-separated, manganese oxide-rich sediments from Gullmar Fjord (Sweden), Skagerrak (Norway) and Ulleung Basin (Korea) were analyzed by 16S rRNA-stable isotope probing (SIP). Manganese reduction was the prevailing terminal electron-accepting process in anoxic incubations of surface sediments, and even the addition of acetate stimulated neither iron nor sulfate reduction. The three geographically distinct sediments harbored surprisingly similar communities of acetate-utilizing manganese-reducing bacteria: 16S rRNA of members of the genera Colwellia and Arcobacter and of novel genera within the Oceanospirillaceae and Alteromonadales were detected in heavy RNA-SIP fractions from these three sediments. Most probable number (MPN) analysis yielded up to 10⁶ acetate-utilizing manganese-reducing cells cm⁻³ in Gullmar Fjord sediment. A 16S rRNA gene clone library that was established from the highest MPN dilutions was dominated by sequences of Colwellia and Arcobacter species and members of the Oceanospirillaceae, supporting the obtained RNA-SIP results. In conclusion, these findings strongly suggest that (i) acetate-dependent manganese reduction in manganese oxide-rich sediments is catalyzed by members of taxa (Arcobacter, Colwellia and Oceanospirillaceae) previously not known to possess this physiological function, (ii) similar acetate-utilizing manganese reducers thrive in geographically distinct regions and (iii) the identified manganese reducers differ greatly from the extensively explored iron reducers in marine sediments.     

Minireview: The Potential of Enhanced Manganese Redox Cycling for Sediment Oxidation

Both natural and anthropogenic processes are responsible for excessive organic loading of submerged soils, with detrimental environmental consequences. The often insufficient natural attenuation can be enhanced by exploiting microbial manganese cycles. This review describes how an anoxic oxidation of organic matter with concomitant reduction of MnO ₂ can link up with a reoxidation of the resulting, soluble Mn(II) in oxic layers. The potentially attainable oxidation rates through these natural cycles are of the same order as the organic carbon accumulation rates. The microbiology and physiology of the responsible organisms are discussed, as well as examples of naturally occurring manganese cycles and the possibility to engineer this natural phenomenon.     

Plant extract-mediated biogenic synthesis of silver,manganese dioxide,silver-doped manganese dioxide nanoparticles and their antibacterial activity against food- and water-borne pathogens

Silver nanoparticles (AgNPs), manganese dioxide nanoparticles (MnO₂NPs) and silver-doped manganese dioxide nanoparticles (Ag-doped MnO₂NPs) were synthesized by simultaneous green chemistry reduction approach. Aqueous extract from the leaves of medicinally important plant Cucurbita pepo was used as reducing and capping agents. Various characterization techniques were carried out to affirm the formation of nanoparticles. HR-TEM analysis confirmed the size of nanoparticles in the range of 15–70 nm and also metal doping was confirmed through XRD and EDS analyses. FT-IR analysis confirmed that the presence of biomolecules in the aqueous leaves extract was responsible for nanoparticles synthesis. Further, the concentration of metals and their doping in the reaction mixture was achieved by ICP–MS. The growth curve and well diffusion study of synthesized nanoparticles were performed against food- and water-borne Gram-positive and Gram-negative bacterial pathogens. The mode of interaction of nanoparticles on bacterial cells was demonstrated through Bio-TEM analysis. Interestingly, AgNPs and Ag-doped MnO₂ NPs showed better antibacterial activity against all the tested bacterial pathogens; however, MnO₂NPs alone did not show any antibacterial properties. Hence, AgNPs and Ag-doped MnO₂ NPs synthesized from aqueous plant leaves extract may have important role in controlling various food spoilage caused by bacteria.     

Distinguishable root plaque on root surface of Potamogeton crispus grown in two sediments with different nutrient status

The properties of plaques were different on the root surface of Potamogeton crispus planted in sediments from two different shallow lakes. Lake Tangxunhu sediment, with low pH, contained low organic matter, whereas Lake Yuehu sediment, with high pH, had high calcium deposits mixed with high organic matter. The contents of mineral elements in sediment of Lake Tangxunhu was lower than that of Lake Yuehu, except for iron (Fe) content, but the contents of mineral elements extracted by sodium dithionite–sodium citrate–sodium bicarbonate (DCB) from root plaques were higher in Lake Tangxunhu than those in Lake Yuehu, except for Fe. These element distributions on P. crispus root plaques were characterized by scanning electron microscope combined with energy-dispersive X-ray spectrometer and were consistent with the contents of mineral elements in sediment. The root plaque of P. crispus planted in Lake Tangxunhu sediment mainly contained silicon (Si) and Fe, and the content of Si was greater than Fe, which may be contributed to the formation of poly-silicic-ferric in the natural conditions. However, the root plaque of P. crispus planted in the sediment with higher calcium content of Lake Yuehu was rich in Fe, Si, phosphorus (P), and calcium (Ca). Due to oxygen secretion by plant roots, the root plaque has more Fe₃(PO₄)₂ and a certain amount of Ca₃(PO₄)₂. The ratio of magnesium (Mn) to Fe extracted by DCB from root plaque in Lake Tangxunhu sediment was 0.031 and 0.010 in Lake Yuehu sediment. In Lake Tangxunhu sediment, lower content of organic matter results in weak reducibility. Enhanced oxidation ability by oxygen secretion of P. crispus root could oxidize low-valent Fe and Mn into iron–manganese oxide, which leads to formation of iron–manganese plaque on the root surface. However, this case is different in Lake Yuehu sediment, where Fe and Mn can be reduced in high organic sediment and low-valent Mn can precipitate in the sediment in which pH is >8. Thus, low-valent Fe in Lake Yuehu sediment moves to the root surface of P. crispus, where it oxidizes into Fe oxide, i.e., Fe plaque.     

Biogenic Manganese Oxides Facilitate Iodide Oxidation at pH ≤ 5

Radioactive ¹²⁹I, a byproduct of nuclear power generation, can pose risks to human health if released into the environment, where its mobility is highly dependent on speciation. Based on thermodynamic principles, ¹²⁹I should exist primarily as iodide (I^?) in most terrestrial environments; however, organo-¹²⁹I and ¹²⁹iodate are also commonly detected in contaminated soils and groundwater. To investigate the capability of biogenic manganese oxides to influence iodide speciation, 17 manganese-oxidizing bacterial strains, representing six genera, were isolated from soils of the Savannah River Site, South Carolina. The isolates produced between 2.6 and 67.1 nmole Mn oxides (ml^?1 media after 25 days, pH 6.5). Results from inhibitor assays targeting extracellular enzymes and reactive oxygen species indicated that both play a role in microbe-induced Mn(II) oxidation among the strains examined. Iodide oxidation was not observed in cultures of the most active Mn-oxidizing bacteria, Chryseobacterium sp. strain SRS1 and Chromobacterium sp. strain SRS8, or the fungus, Acremonium strictum strain KR21–2. While substantial amounts of Mn(III/IV) oxides were only generated in cultures at ≥pH 6, iodide oxidation was only observed in the presence of Mn(III/IV) oxides when the pH was ≤5. Iodide oxidation was promoted to a greater extent by synthetic Mn(IV)O₂ than biogenic Mn(III/IV) oxides under these low pH conditions (≤pH 5). These results indicate that the influence of biogenic manganese oxides on iodide oxidation and immobilization is primarily limited to low pH environments.     

Portraying manganese biofilms via a merger of EPR spectroscopy and cathodic polarization

Microbial biofilms on stainless steel surfaces exposed to water from a freshwater pond were dominated by manganese-oxidizing bacteria, as initially diagnosed by microscopy and elemental analysis. The application of electron paramagnetic resonance (EPR) spectroscopy revealed conspicuous sextet (six-line) patterns that intensified with immersion time, implying the gradual accumulation of Mn(II) in the biofilms. Correspondingly, cathodic polarization designated the manganese oxide (MnO_x) reduction peak in the form of a distinctive ‘nose’, which grew increasingly more negative with biofilm growth. The progressive expansion of cathodic current densities and the concurrent area-under-the-curve also allowed the quantification of microbially mediated MnO_x deposition_. Furthermore, the merger of EPR and cathodic polarization techniques yielded key insights, in tandem with Mn speciation data, into the pathways of microbial manganese transformations in biofilms, besides providing meaningful interpretations of prevailing literature. Accordingly, the natural freshwater biofilm was inferred as one supporting a complete manganese cycle encompassing multiple redox states.     

The effect of manganese-oxidizing bacteria and pH on the availability of manganous ions and manganese oxides to oats in nutrient solutions

Summary The uptake of Mn from manganous ions (Mn-ions) and pyrolusite (MnO₂) by three week-old oat plants (Avena sativa L.) grown in nutrient solutions controlled at pH values between 6 and 8, was almost completely inhibited by suspensions of Mn- oxidizing bacteria over a three day uptake period.Grey speck symptoms of Mn deficiency developed in oats grown for 10 days with Mn bacteria in a nutrient solution that had received 1 ppm Mn ions and was controlled at pH 6.3. Rape plants (Brassica napus L.) absorbed appreciable amounts of Mn from treatments similar to those that inhibited Mn uptake by oats.Treatments which decreased or prevented biological oxidation of Mn ions favoured the uptake of Mn by oats from Mn ions, MnO₂ and bacterial Mn-oxide. Acid conditions (pH 5.0) always increased Mn uptake. This was due in part to inhibition of bacterial oxidation and to an increase in the ability of the plants to obtain Mn from Mn oxides.Uptake of Mn is explained on the basis of the rates of two opposing processes; the rate of release of Mn from oxides and the rate of biological oxidation of Mn ions. The results are discussed in relation to the availability of Mn in soils.     

Bacterial Communities of Three Saline Meromictic Lakes in Central Asia

Meromictic lakes located in landlocked steppes of central Asia (~2500 km inland) have unique geophysiochemical characteristics compared to other meromictic lakes. To characterize their bacteria and elucidate relationships between those bacteria and surrounding environments, water samples were collected from three saline meromictic lakes (Lakes Shira, Shunet and Oigon) in the border between Siberia and the West Mongolia, near the center of Asia. Based on in-depth tag pyrosequencing, bacterial communities were highly variable and dissimilar among lakes and between oxic and anoxic layers within individual lakes. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Firmicutes were the most abundant phyla, whereas three genera of purple sulfur bacteria (a novel genus, Thiocapsa and Halochromatium) were predominant bacterial components in the anoxic layer of Lake Shira (~20.6% of relative abundance), Lake Shunet (~27.1%) and Lake Oigon (~9.25%), respectively. However, few known green sulfur bacteria were detected. Notably, 3.94% of all sequencing reads were classified into 19 candidate divisions, which was especially high (23.12%) in the anoxic layer of Lake Shunet. Furthermore, several hydro-parameters (temperature, pH, dissolved oxygen, H₂S and salinity) were associated (P< 0.05) with variations in dominant bacterial groups. In conclusion, based on highly variable bacterial composition in water layers or lakes, we inferred that the meromictic ecosystem was characterized by high diversity and heterogenous niches.     

Bacteriology of manganese nodules: III. Reduction of MnO(2) by two strains of nodule bacteria

MnO₂ reduction by aerobic growing cultures of Bacillus 29 and coccus 32, isolated from ferromanganese nodules, was assessed for 7 days. A 1-day lag was observed before the onset of MnO₂ reduction by either culture. Addition of HgCl₂ to a final concentration of about 10^-3 M caused a rapid cessation of MnO₂ reduction by the growing cultures. Neither culture reduced MnO₂ when grown under continued anaerobiosis from the start of an experiment. However, if conditions were made anaerobic after MnO₂ reduction was initiated, reduction continued at a rate only slightly lower than that under aerobic conditions. Resting-cell cultures reduced MnO₂ equally well aerobically and anaerobically, provided that ferricyanide was present to serve as electron carrier. These findings showed that oxygen is needed for culture adaptation to MnO₂ reduction, and that oxygen does not interfere with microbial MnO₂ reduction itself. Both cultures caused sharp drops in the pH of the medium during MnO₂ reduction: with coccus 32, during the entire incubation time; with Bacillus 29, for the first 3 days. The E_h of the medium fluctuated with either culture and never fell below 469 mv with Bacillus 29 and below 394 mv with coccus 32. The rates of glucose consumption and Mn²⁺ release by Bacillus 29 and coccus 32 were fairly constant, but the rates of lactate and pyruvate production were not. Although acid production undoubtedly helped in the reduction of pyrolusite (MnO₂) by the bacteria, it did not appear to be important in the reduction of manganese oxide in ferromanganese nodules, as shown by the results with a nodule enrichment.     

Bacteriology of Manganese Nodules: III. Reduction of MnO2 by Two Strains of Nodule Bacteria1

MnO₂ reduction by aerobic growing cultures of Bacillus 29 and coccus 32, isolated from ferromanganese nodules, was assessed for 7 days. A 1-day lag was observed before the onset of MnO₂ reduction by either culture. Addition of HgCl₂ to a final concentration of about 10^-3 M caused a rapid cessation of MnO₂ reduction by the growing cultures. Neither culture reduced MnO₂ when grown under continued anaerobiosis from the start of an experiment. However, if conditions were made anaerobic after MnO₂ reduction was initiated, reduction continued at a rate only slightly lower than that under aerobic conditions. Resting-cell cultures reduced MnO₂ equally well aerobically and anaerobically, provided that ferricyanide was present to serve as electron carrier. These findings showed that oxygen is needed for culture adaptation to MnO₂ reduction, and that oxygen does not interfere with microbial MnO₂ reduction itself. Both cultures caused sharp drops in the pH of the medium during MnO₂ reduction: with coccus 32, during the entire incubation time; with Bacillus 29, for the first 3 days. The E_h of the medium fluctuated with either culture and never fell below 469 mv with Bacillus 29 and below 394 mv with coccus 32. The rates of glucose consumption and Mn²⁺ release by Bacillus 29 and coccus 32 were fairly constant, but the rates of lactate and pyruvate production were not. Although acid production undoubtedly helped in the reduction of pyrolusite (MnO₂) by the bacteria, it did not appear to be important in the reduction of manganese oxide in ferromanganese nodules, as shown by the results with a nodule enrichment.     

The successive reduction of Cr(VI) and NO 3 − or Mn(IV) ions present in the cultivation medium of denitrifying bacteria

A study of the reduction of chromium (VI) and manganese (IV) (or nitrate) ions present in the cultivation medium of denitrifying bacteria of the genus Pseudomonas showed that Cr(VI) ions are reduced first. The rate of Cr(VI) reduction was found to be independent of the presence of Mn(IV) or nitrate ions in the medium.     

Physiology and kinetics of manganese‐reducing bacillus polymyxa strain D1 isolated from manganiferous silver ore

Manganese‐reducing bacteria were isolated from a manganiferous silver ore mining site using enrichment procedures. The most rapid Mn(IV) reducer was identified as Bacillus polymyxa and was designated as strain D1. Isolate D1 has no growth‐factor requirements and is mesophilic and neutrophilic. D1 respires glucose aerobically, under which conditions cyanide is bactericidal. Nonfermentable substrates such as lactate, acetate, citrate, and succinate cannot serve as sole carbon sources. D1 ferments glucose anaerobically, producing acetic acid, ethanol, and butanediol as major metabolic end products. Both anaerobic conditions and direct physical contact with pyrolusite (MnO₂) particles were necessary for manganese reduction. Strain D1 is unique in that manganese serves as an ancillary electron acceptor during anaerobic fermentation. Kinetic experiments showed that D1 reduced manganese three to five times as rapidly as the widely studied Mn(IV)/Fe(III)‐reducing microorganisms Shewanella putrefaciens MR‐1 and Shewanella putrefa‐ciens sp. 200. Strain D1 is capable of liberating silver via the reductive dissolution of refractory manganiferous ores.     

Development of Genus/Species-Specific PCR Analysis for Identification of <Emphasis Type="Italic">Carnobacterium</Emphasis> Strains

Heterofermentative lactic acid bacteria belonging to the genus Carnobacterium are currently divided into seven different species, C. piscicola, C. mobile, C. gallinarum, C. inhibens, C. divergens, C. funditum, and C. alterfunditum. 16S rDNA-targeted PCR assay was carried out for the identification of the genus Carnobacterium. In addition, type strains of all Carnobacterium species were analyzed by 16S–23S rDNA intergenic spacer analysis in comparison with type strains of phylogenetically related lactic acid bacteria. These methods enabled the identification and the discrimination among Carnobacterium species and the other phylogenetically related lactic acid bacteria. Likewise, analogous results were obtained by restriction analysis of amplified 16S rDNA performed with HaeIII and HinfI as restriction enzymes. Received: 25 July 2001 / Accepted: 19 October 2001     

Fungal oxidative dissolution of the Mn(II)‐bearing mineral rhodochrosite and the role of metabolites in manganese oxide formation

Microbially mediated oxidation of Mn(II) to Mn(III/IV) oxides influences the cycling of metals and remineralization of carbon. Despite the prevalence of Mn(II)‐bearing minerals in nature, little is known regarding the ability of microbes to oxidize mineral‐hosted Mn(II). Here, we explored oxidation of the Mn(II)‐bearing mineral rhodochrosite (MnCO₃) and characteristics of ensuing Mn oxides by six Mn(II)‐oxidizing Ascomycete fungi. All fungal species substantially enhanced rhodochrosite dissolution and surface modification. Mineral‐hosted Mn(II) was oxidized resulting in formation of Mn(III/IV) oxides that were all similar to δ‐MnO₂ but varied in morphology and distribution in relation to cellular structures and the MnCO₃ surface. For four fungi, Mn(II) oxidation occurred along hyphae, likely mediated by cell wall‐associated proteins. For two species, Mn(II) oxidation occurred via reaction with fungal‐derived superoxide produced at hyphal tips. This pathway ultimately resulted in structurally unique Mn oxide clusters formed at substantial distances from any cellular structure. Taken together, findings for these two fungi strongly point to a role for fungal‐derived organic molecules in Mn(III) complexation and Mn oxide templation. Overall, this study illustrates the importance of fungi in rhodochrosite dissolution, extends the relevance of biogenic superoxide‐based Mn(II) oxidation and highlights the potential role of mycogenic exudates in directing mineral precipitation.     

Enzymatic Manganese(II) Oxidation by Metabolically Dormant Spores of Diverse Bacillus Species

Bacterial spores are renowned for their longevity, ubiquity, and resistance to environmental insults, but virtually nothing is known regarding whether these metabolically dormant structures impact their surrounding chemical environments. In the present study, a number of spore-forming bacteria that produce dormant spores which enzymatically oxidize soluble Mn(II) to insoluble Mn(IV) oxides were isolated from coastal marine sediments. The highly charged and reactive surfaces of biogenic metal oxides dramatically influence the oxidation and sorption of both trace metals and organics in the environment. Prior to this study, the only known Mn(II)-oxidizing sporeformer was the marine Bacillus sp. strain SG-1, an extensively studied bacterium in which Mn(II) oxidation is believed to be catalyzed by a multicopper oxidase, MnxG. Phylogenetic analysis based on 16S rRNA and mnxG sequences obtained from 15 different Mn(II)-oxidizing sporeformers (including SG-1) revealed extensive diversity within the genus Bacillus, with organisms falling into several distinct clusters and lineages. In addition, active Mn(II)-oxidizing proteins of various sizes, as observed in sodium dodecyl sulfate-polyacrylamide electrophoresis gels, were recovered from the outer layers of purified dormant spores of the isolates. These are the first active Mn(II)-oxidizing enzymes identified in spores or gram-positive bacteria. Although extremely resistant to denaturation, the activities of these enzymes were inhibited by azide and o-phenanthroline, consistent with the involvement of multicopper oxidases. Overall, these studies suggest that the commonly held view that bacterial spores are merely inactive structures in the environment should be revised.     

Sulfate-Reducing Bacteria and Their Activities in Cyanobacterial Mats of Solar Lake (Sinai, Egypt)

The sulfate-reducing bacteria within the surface layer of the hypersaline cyanobacterial mat of Solar Lake (Sinai, Egypt) were investigated with combined microbiological, molecular, and biogeochemical approaches. The diurnally oxic surface layer contained between 10⁶ and 10⁷ cultivable sulfate-reducing bacteria ml⁻¹ and showed sulfate reduction rates between 1,000 and 2,200 nmol ml⁻¹ day⁻¹, both in the same range as and sometimes higher than those in anaerobic deeper mat layers. In the oxic surface layer and in the mat layers below, filamentous sulfate-reducing Desulfonema bacteria were found in variable densities of 10⁴ to 10⁶ cells ml⁻¹. A Desulfonema-related, diurnally migrating bacterium was detected with PCR and denaturing gradient gel electrophoresis within and below the oxic surface layer. Facultative aerobic respiration, filamentous morphology, motility, diurnal migration, and aggregate formation were the most conspicuous adaptations of Solar Lake sulfate-reducing bacteria to the mat matrix and to diurnal oxygen stress. A comparison of sulfate reduction rates within the mat and previously published photosynthesis rates showed that CO₂ from sulfate reduction in the upper 5 mm accounted for 7 to 8% of the total photosynthetic CO₂ demand of the mat.     

FTIR Spectroscopic Study of Biogenic Mn-Oxide Formation by Pseudomonas putida GB-1

Biomineralization in heterogeneous aqueous systems results from a complex association between pre-existing surfaces, bacterial cells, extracellular biomacromolecules, and neoformed precipitates. Fourier transform infrared (FTIR) spectroscopy was used in several complementary sample introduction modes (attenuated total reflectance [ATR], diffuse reflectance [DRIFT], and transmission) to investigate the processes of cell adhesion, biofilm growth, and biological Mn-oxidation by Pseudomonas putida strain GB-1. Distinct differences in the adhesive properties of GB-1 were observed upon Mn oxidation. No adhesion to the ZnSe crystal surface was observed for planktonic GB-1 cells coated with biogenic MnO _x , whereas cell adhesion was extensive and a GB-1 biofilm was readily grown on ZnSe, CdTe, and Ge crystals prior to Mn-oxidation. IR peak intensity ratios reveal changes in biomolecular (carbohydrate, phosphate, and protein) composition during biologically catalyzed Mn-oxidation. In situ monitoring via ATR-FTIR of an active GB-1 biofilm and DRIFT data revealed an increase in extracellular protein (amide I and II) during Mn(II) oxidation, whereas transmission mode measurements suggest an overall increase in carbohydrate and phosphate moieties. The FTIR spectrum of biogenic Mn oxide comprises Mn-O stretching vibrations characteristic of various known Mn oxides (e.g., “acid” birnessite, romanechite, todorokite), but it is not identical to known synthetic solids, possibly because of solid-phase incorporation of biomolecular constituents. The results suggest that, when biogenic MnO _x accumulates on the surfaces of planktonic cells, adhesion of the bacteria to other negatively charged surfaces is hindered via blocking of surficial proteins.