Role Of Microbial Activity Research Articles

Iron and carbon isotope evidence for microbial iron respiration throughout the Archean

Banded Iron-Formations (BIFs) are voluminous chemical sediments that are rich in iron-oxide, carbonate and silica and whose occurrence is unique to the Precambrian. Their preservation in the geological record offers insights to the surface chemical and biological cycling of iron and carbon on early Earth. However, many details regarding the role of microbial activity in BIF deposition and diagenesis are unresolved. Laboratory studies have shown that reaction between carbon and iron through microbial iron respiration [2Fe 2O 3∙ nH 2O + CH 2O + 7H + → 4Fe 2+ + HCO 3 − + (2n + 4)H 2O + chemical energy] can impart fractionation to the isotopic compositions of these elements. Here, we report iron (δ 56Fe, vs. IRMM-014) and carbon isotopic (δ 13C, vs. V-PDB) compositions of magnetite and of iron-rich and iron-poor carbonates in BIFs from the late Archean (~ 2.5 Ga) Hamersley Basin, Australia and the early Archean (~ 3.8 Ga) Isua Supracrustal Belt (ISB), Greenland. The range of δ 56Fe values measured in the Hamersley Basin, including light values in magnetite and heavy values in iron-rich carbonates (up to + 1.2‰), are incompatible with their precipitation in equilibrium with seawater. Rather, the data together with previously reported light δ 13C values in iron-rich carbonates record evidence for diagenetic reduction of ferric oxide precursors to magnetite and carbonate through microbial iron respiration (i.e., dissimilatory iron reduction, DIR). Iron and carbon isotope data of iron-rich metacarbonates from the ISB are similar to those of late Archean BIFs. The isotopic signatures of these metacarbonates are supportive of an early diagenetic origin despite metasomatic overprint, and preserve evidence of microbial iron respiration within the oldest recognized sedimentary rocks on Earth.

Microbial corrosion of P235GH steel under geological conditions

The role of microbial activity on the alteration of steel containers used for nuclear waste disposal is increasingly discussed. In this work we isolated and identified sulphate-reducing bacteria (SRB) in the Callovo–Oxfordian clay rock studied as a potential host rock formation for a repository for high-level and long-lived radioactive waste in France. Then, the effect of the SRB growth on the overpack steel corrosion was investigated. The corrosion rate of the steel coupons was high under biotic conditions (∼30 μm/year) in comparison to blank sterilized runs (∼14 μm/year). Culture experiments in compacted conditions with clay–stone cores and steel coupons under 120 bar, simulating deep geological conditions, gave results similar to those obtained in batch experiments (e.g. production of H 2S). This indicates the plausibility of SRB growth during the construction and operational phases of the repository and their survival at least temporarily after the disposal closure if water is available, which may cause fast corrosion of the steel containers under disposal conditions.

Microbial distribution and diversity in saturated, high pH, uranium mine tailings, Saskatchewan, Canada

Microbiological analyses were conducted on core samples collected along a vertical profile (0-66 m below surface) from the tailings management facility (TMF) at the Rabbit Lake uranium mine in northern Saskatchewan, Canada. Bacterial numbers in the core materials were similar to surrounding soils and surface waters, regardless of the seemingly unfavorable pH (mean=9.9) and temperature (approximately 0 degrees C) in the TMF. The greatest number of viable cells (105 CFU/g) was detected at the interface between the tailings and overlying standing water, below which cell counts decreased rapidly with depth. Whole-community metabolic profiles for samples from the different depths grouped into 3 clusters; however, these groups could not be positively correlated with sampling depth, temperature, redox potential, pH, or ore-mill feed. Flow-cell studies demonstrated microbial communities in the tailings surface water could develop biofilms and maintain cell activity at both pH 10 and 7, and altering the pH between these 2 values had little effect on biofilm viability. These results demonstrate the resilience and adaptive nature of naturally occurring microbial communities and signify a potential role of microbial activity in the long-term geochemical evolution of the TMF.

57Fe as a Tracer of Bacterially Mediated Iron Mobilization in Lake Sediments

In simulation experiments the stable isotope, 57 Fe, was used as a novel tracer of iron transport to investigate the role of microbial activity on the distribution/redistribution of metals in lake sediments. A series of microcosm sediment columns was set up, containing a layer of 57 Fe-labelled ferrihydrite to track iron mobility temporally. Three series of columns were prepared, one set with unamended homogenized lake sediments, one set amended with 57 Fe-labelled ferrihydrite in the bottom layer of the column and one abiotic control set amended with 57 Fe-labelled ferrihydrite which was sterilized. During the experiments the iron concentrations increased in the upper sediment layers, pore water and overlying lake water and decreased in the lower amended sediment layer. The distribution of 57 Fe in the abiotic cores did not change during the experiment, implying that physical disturbance during sampling and chemical iron reduction and remobilization can be excluded as causes for the changes in iron distribution in the biotic cores. Thus, the remobilization and deposition of iron in the columns was initiated by microbial redox reactions. The implications of this work are significant for the interpretation of metal profiles in fresh water sediments as historical records of metal loadings, particularly because redox-sensitive amorphous Fe and Mn oxides and oxyhydroxides can serve as sites for metal adsorption or co-precipitation.

Role of Microbial Activity in Fe and S Cycling in Sub-Oxic to Anoxic Sulfide-Rich Mine Tailings

Acid-mine drainage is an important environmental problem associated with base-metal mining and numerous studies have looked at the chemical and microbial processes involved in the oxidation of metal sulfides under oxic conditions. However, little is known about the activity of bacteria living in the same sulfide-rich tailings, but under sub-oxic to anoxic conditions. Recent work on Cu-Zn mine tailings have shown that sulfate-reducing bacteria (SRB) are present and active in these tailings (under a wide range of pH conditions) and that their activity is season dependent. In fact, acidic conditions and low organic carbon availability in the spring tend to greatly limit the activity of SRB in the tailings. On the other hand, IRB populations tend to increase in number in the spring, maybe as a result of the lack of activity of SRB. These findings are in agreement with studies on acidic coal mining lakes in Germany, which showed that IRB were mainly active in acidic and oxic sediments whereas SRB dominated in the more anoxic and pH neutral sediments. The presence and activity of SRB and IRB also represents a potential bioremediation tool, because both microbial pathways generate alkalinity. Recent work on acidic mining lakes indicates that IRB and SRB activity could be enhanced in a control manner and be used as an acidity neutralizing process to treat environments impacted by AMD.

Degradation of picric acid and 2,6-DNT in marine sediments and waters: the role of microbial activity and ultra-violet exposure

Bio- and photo-transformation of two munitions and explosives of concern, 2,6-dinitrotoluene (2,6-DNT) and 2,4,6-trinitrophenol (picric acid) were assessed in spiked marine sediments and water. A sandy and a fine-grained sediment, with 0.25% and 1.1% total organic carbon, respectively, were used for biotransformation assessments at 10 and 20 °C. Sterilized sediments were used as controls for biotic vs. abiotic transformation. Transformation products were analyzed by HPLC, GC/MS and LC/MS. Biotransformation in sediments started soon after the initial contact of the chemicals with the sediments and proceeded for several months, with rates in the following sequence: fine-grain at 20 °C > fine-grain at 10 °C > sand at 20 °C > sand at 10 °C. The biotransformation paths seemed to be similar for all conditions. The major biotransformation product of 2,6-DNT was 2-amino-6-nitrotoluene (2-A-6-NT). 2-Nitrotoluene (2-NT) and other minor components, including N, N-dimethyl-3-nitroaniline, benzene nitrile, methylamino-2-nitrosophenol and diaminophenol, were also identified. After more prolonged incubation these chemicals were replaced by high molecular weight polymers. Several breakdown products of picric acid were identified by GC/MS, including 2,4-dinitrophenol, amino dinitrophenols, 3,4-diamino phenol, amino nitrophenol and nitro diaminophenol. Photo-transformation of 2,6-DNT and picric acid in seawater was assessed under simulated solar radiation (SSR). No significant photolysis of picric acid in seawater was observed for up to 47 days, but photo-transformation of 2,6-DNT began soon after the initial exposure to SSR, with 89% being photo-transformed in 24 h and none remaining after 72 h. High molecular weight chemicals were generated, with mass spectra ranging from molecular weight 200–500 compared to 182 for DNT, and the color of the stock solution changed from clear to orange. Complexity of the mass spectra and mass differences among fragments suggest that multiple polymers were produced and were co-eluting during the LC/MS analyses.

Effect of soil moisture at different temperatures on Rhizoctonia root rot of wheat seedlings

The effect of soil moisture at different temperatures on root rot of wheat seedlings caused by Rhizoctonia solani AG-8 was studied in temperature controlled water tanks under glasshouse conditions. Four moisture levels (15, 30, 50 and 75% of soil water holding capacity at saturation which were equal to −10, −7, −5 and −3 kPa, respectively) were tested in tanks maintained 10, 15, 20 or 25 °C. The role of microbial activity in the effect of soil moisture and temperature on disease severity was also studied by including treatments of steam treated soil. Results showed that at soil moisture levels optimum for plant growth (50 and 75% WHC) disease was more severe at a lower temperature (10 °C), but under relatively dry conditions (15% WHC) disease levels were similar at all temperatures tested. In warm soils (20 and 25 °C) at high soil moisture levels (50 and 75% WHC), disease was more severe in steam treated soil than in non-steam treated soil, indicating that the suppression of disease in natural soil under these conditions was associated with high soil microbial activity.

Performance, Water Use and Effluent Output of Weaner Pigs Fed ad libitumwith Either Dry Pellets or Liquid Feed and the Role of Microbial Activity in the Liquid Feed

Forty eight and ninety six pigs weaned at 22.6 ± 2.6 days, were allocated to two trials to study the effect of feeding post-weaning diets ad libitum, either as dry pellets (DF) or as meal mixed with water in the ratio 2.5 :1 (LF). The trials, lasting 28 days, differed only in the type of trough used to present the liquid feed to the pigs. In both trials the daily gain of LF pigs over the 4 weeks of the trial was significantly (P < 0.001) better than that of the DF pigs. Daily gains for the two treatment groups were respectively 428 and 343 ± 15 g day -1 in Trial 1 and 454 and 397 ± 10 g day -1 in Trial 2. The feed conversion ratio (FCR) (corrected to fresh weight of dry feed) of LF pigs was significantly poorer (P<0.01) than that of DF pigs in both trials primarily as a result of feed wastage by the LF pigs. FCR for the DF and LF pigs was, respectively, 1.31 and 1.89 ± 0.05 in Trial 1. In Trial 2 improvements in the trough design reduced the difference in FCR. FCR for the DF and LF treatments was 1.37 and 1.44 ± 0.02 respectively. In Trials 1 and 2 LF pigs used on average 76% and 35% more water than DF pigs. LF pig produced 12% (Trial 1) and 5.7% (Trial 2) more effluent per unit of liveweight gain than DF pigs. Microbiological examination of the liquid feed system demonstrated that the system acted as a fermenter. Lactobacillus spp proliferated rapidly and became the dominant organism within 5 days and the populations remained relatively constant thereafter. The proliferation of lactobacilli reduced the pH of the liquid feed from approximately 6.0 to between 3.5 and 4.0. At the lower levels of pH the number of coliforms in the feed was significantly reduced.

Performance, Water Use and Effluent Output of Weaner Pigs Fed ad libitum with Either Dry Pellets or Liquid Feed and the Role of Microbial Activity in the Liquid Feed

Forty eight and ninety six pigs weaned at 22·6±2·6 days, were allocated to two trials to study the effect of feeding post-weaning diets ad libitum, either as dry pellets (DF) or as meal mixed with water in the ratio 2·5:1 (LF). The trials, lasting 28 days, differed only in the type of trough used to present the liquid feed to the pigs. In both trials the daily gain of LF pigs over the 4 weeks of the trial was significantly (P<0·001) better than that of the DF pigs. Daily gains for the two treatment groups were respectively 428 and 343±15 g day−1 in Trial 1 and 454 and 397±10 g day−1 in Trial 2. The feed conversion ratio (FCR) (corrected to fresh weight of dry feed) of LF pigs was significantly poorer (P<0·01) than that of DF pigs in both trials primarily as a result of feed wastage by the LF pigs. FCR for the DF and LF pigs was, respectively, 1·31 and 1·89±0·05 in Trial 1. In Trial 2 improvements in the trough design reduced the difference in FCR. FCR for the DF and LF treatments was 1·37 and 1·44±0·02 respectively. In Trials 1 and 2 LF pigs used on average 76% and 35% more water than DF pigs. LF pig produced 12% (Trial 1) and 5·7% (Trial 2) more effluent per unit of liveweight gain than DF pigs. Microbiological examination of the liquid feed system demonstrated that the system acted as a fermenter.Lactobacillusspp proliferated rapidly and became the dominant organism within 5 days and the populations remained relatively constant thereafter. The proliferation of lactobacilli reduced the pH of the liquid feed from approximately 6·0 to between 3·5 and 4·0. At the lower levels of pH the number of coliforms in the feed was significantly reduced.

Evidence for microbial influence on the development of Lower Carboniferous buildups

Abstract Following a series of mass extinction events towards the end of the Devonian (Frasnian), true skeletal reef-building organisms were effectively lost from latest Devonian (Famennian) and Lower Carboniferous (Dinantian) marine ecosystems. Nevertheless, nonskeletal, mud-dominated buildups (mud-mounds) are common throughout this geological interval, and microbial activity (fungi, algae and/or bacteria) is considered to have played a significant role in the development of these buildups. Evidence of microbial activity in Dinantian buildups may be divided into two broad categories: (a) direct evidence, such as the development of stromatolitic and thrombolitic macrostructures, presence of cryptic incrustations and preservation of calcimicrobes such as Renalcis ; (b) cryptic evidence, in the form of peloidal ‘mud’ which forms the matrix of many Dinantian buildups. The matrix peloidal micrites closely resemble modern microbially mediated (algal and bacterial) carbonate precipitates. Precipitation of the peloidal fabrics is considered to have occurred within a microbial mat that bound the accreting buildup surface, thereby allowing steep depositional slopes to develop in deep water buildups and protecting shallow water buildups from erosion. Extensive cavity systems, often developed in Dinantian buildups, may also contain stromatolitic mats and micritized cavity walls. These fabrics indicate the additional presence of internal heterotrophic microbial communities and suggest that a diverse range of microbes were present in Dinantian buildups. Controls on the development of Dinantian buildups are likely to have been multiple. Nutrient-rich (mesotrophic) water masses, in combination with relatively low sedimentation rates, may have promoted buildup initiation, while regional palaeogeography and tectonic events played a role in their location. Tournaisian buildups commonly developed in a wide range of water depths on carbonate ramps, whereas Viséan buildups, particularly in northwestern Europe, were often restricted to relatively shallow water over tectonically controlled topographic highs. Evolution of new organisms during mid-Carboniferous time led to a diversification of buildup types. However, microbial fabrics identical to those developed in Dinantian buildups are still present in many late Carboniferous and Permian phylloid algal, Palaeoaplysina and bryozoan buildups. The role of microbial activity in the development of these late Carboniferous and Permian buildups may have been greatly underestimated.

Spatial and temporal variability of soil respiration in agricultural fields

Chamber measurements of CO2 evolution were made on bare soil, and in maize (1988) and wheat (1989) crops in order to study the spatial and temporal variability of soil respiration (Rsoil). Semivariograms showed no definite structure of spatial autocorrelation on bare soil when measurements were made along transects. Spatial variability was shown to occur at a scale smaller than 15 cm. In a maize crop, Rsoil in the row was significantly higher (P = 0.05) than in the interrow when the soil surface was dry. Under wet soil conditions, Rsoil in the interrow compacted by the tractor wheel was lower (P = 0.05) than on noncompacted soil and no significant difference was found between rows and interrows. These observations were attributed to the contribution of plant roots to Rsoil in dry conditions. In wetter soil, the role of microbial activity was dominant except in the compacted interrow where lower airfilled porosity caused lower Rsoil. Random measurements in a wheat crop over the growing season showed that the number of samples needed to estimate the Rsoil of a 1 ha area within 10% (P = 0.05) of its mean value decreased from 190 at the time of seeding to 30 at the end of the season. The maximum Rsoil during the growing season coincided with the period of maximum growth of both crops. A post-rainfall Rsoil burst is also described. Immediately after a 2-h rainfall event, when soil was at field capacity, Rsoil was nine times higher than its level prior to the rainfall and gradually decreased with time. Key words: Soil respiration, variability, chamber measurements, CO2 flux

The Role of Microbial Activity in Suppression of Damping-Off Caused byPythium ultimum

The Role of Microbial Activity in Suppression of Damping-Off Caused by<i>Pythium ultimum</i>

Composting of agricultural wastes for their use as container media: effect of heat treatments on suppression of Pythium aphanidermatum and microbial activities in substrates containing compost

Composted separated manure (CSM) and composted grape marc (CGM) were found to suppress Pythium damping off. This effect was negated by autoclaving the medium, but was restored when compost that had not been autoclaved was mixed with the sterile one. Heat treatment (55°C for 2 h) did not affect suppression even after two growth cycles: in fact, suppression of Pythium in compost and peat mixtures was improved by heating. It is suggested that microorganisms in CSM are more thermostable than peat microflora. Fungal and bacterial counts as well as measurements of biological activities were performed. The CSM microflora was more active than the peat population in terms of fluorescein diacetate hydrolysis and CO 2 evolution. Both activities were less sensitive to 55°C heat treatments in CSM than in peat, but as sensitive as in peat to 80 and 100°C heat treatments. The effect of incubation on the activities was studied and different patterns were observed for CSM and peat. The role of microbial activity in suppression of Pythium is discussed.

Critical review of water activities and microbiology of drying of meats.

The drying of meat is one of the least expensive and most effective ways to preserve meat. This article reviews the influence of intrinsic and extrinsic parameters of foods in relation to the drying of meat and the role of microbial activities in the drying and storage of meat. The critical role of water activity and its relationship with other physical and chemical parameters and microbial survival in the drying of meat is also reviewed in detail. This article ends with a description of the various methods to measure water activity in foods. The conclusion is that the drying of meat is a highly complex phenomenon which is influenced by the composition of meat, its water holding capacity, the processing of meat, and various microorganisms found on meat before and after the drying process. There is no doubt that the drying of meat is an effective preservation process, but attention should be placed on the possible survival of microorganisms in the process in order to prevent spoilage and food-borne diseases.

Microbial mineral maricultures, a possibility?

The theory of submarine soil formation, especially the role of microbial activity in this type of soil formation, seems to open the possibility of using controlled microbial cultures in order to concentrate certain minerals and ores. After discussing in some detail processes of submarine concentration of ore compounds, the microbial aspects of the processes and the practical aspects, as well as the environmental and economical factors, of submarine ore cultivation, by means of microbial aquacultures are dealt with.