Fission-product and cerium uptake by bacteria, yeasts, and molds

Single cell ICP-MS to evaluate the interaction behaviour for Cd, Ce and U with Streptomyces coelicolor spores

Streptomyces are important soil bacteria used for bioremediation of metal-contaminated soils, however, it is still unknown how metal-selective Streptomyces are and which mechanisms are involved during their capture. In this work, we exposed S. coelicolor spores to environmentally relevant concentrations (0.1, 1, 10, 100 μM) of Ce, U and Cd in solid medium for one week to investigate the uptake behaviour of hyphae in the newly formed spores. Additionally, metal adsorption onto the spores was explored by incubating inactive, ungerminated spores for one day in aqueous metal solution. The spore-washing treatment was key to distinguishing between strongly spore-associated (e.g. incorporation; Tris-EDTA buffer) and weakly spore-associated metals (Tris buffer alone minus Tris-EDTA). Single cell (sc) ICP-MS was used to quantify metal-associated content in individual spores. Our results revealed element-specific adsorption onto inactive spores showing that out of the total metal exposure, both strongly (Ce: 58%; U: 54%; Cd: 28%) and weakly (Ce: 12%; U: 1%; Cd: 18%) adsorbed metals occur. However, scICP-MS showed that from metal-amended solid medium, only Ce and U were strongly spore-associated (averages 0.040 and 0.062 fg spore-1 for 10 μM exposures, respectively) while Cd was below the limit of detection (< 0.006 fg spore-1). We propose that hyphae only metabolically interact with Ce in a controlled manner but uncontrolled with U, as 66-73% Ce and only 2-4% U were inherited from adsorbed content. We conclude that Streptomyces spore-metal interaction starts with a relevant adsorption step of Ce, U and Cd as presented for aqueous conditions. If spores start to germinate, hyphae are capable of effectively encapsulating Ce and U, but not Cd. This study brings light into the still unknown field of metal interactions with Streptomyces and applied understanding for more efficient and metal-specific use of Streptomyces in bioremediation of metal-polluted soils.

Diversity, Abundance, and Some Characteristics of Bacteria Isolated from Earth Material Consumed by Wild Animals at Kudurs in the Sikhote-Alin Mountains, Russia

In this work, geochemical and microbiological studies were performed at kudurs in the southeastern part of the Sikhote-Alin mountain range and in the Sikhote-Alin Nature Reserve located in Primorsky Krai, Russia. It was found that the earth material eaten by wild animals in both sites is represented by clay-zeolite tuffs of dacite-rhyolite composition. In the earth material, Na is predominant in bioavailable macronutrients and Zn, light lanthanides, and Y in trace elements. Microbiological studies of geophagic earths revealed a wide range of heterotrophic and autotrophic aerobes and anaerobes involved in the conversion of carbon, nitrogen, and sulfur. Iron- and manganese-oxidizing bacteria and silicate bacteria were identified as well. The isolated pure cultures of heterotrophic bacteria were represented mainly by Gram-positive spore-forming large rods of Bacillus sp. and Gram-negative heterotrophic aerobic and facultative anaerobic microorganisms Burkholderia sp. and Microvirgula aerodenitrificans, which oxidize iron and reduce sulfate. The ability of the bacteria M. aerodenitrificans to reduce sulfates is shown for the first time. According to the literature, the isolated microorganisms are able to actively extract rare earth elements from earth materials, transforming them from the bioinert state to a state accessible to herbivorous mammals.

Metals and Methanotrophy

Aerobic methanotrophs have long been known to play a critical role in the global carbon cycle, being capable of converting methane to biomass and carbon dioxide. Interestingly, these microbes exhibit great sensitivity to copper and rare-earth elements, with the expression of key genes involved in the central pathway of methane oxidation controlled by the availability of these metals. That is, these microbes have a "copper switch" that controls the expression of alternative methane monooxygenases and a "rare-earth element switch" that controls the expression of alternative methanol dehydrogenases. Further, it has been recently shown that some methanotrophs can detoxify inorganic mercury and demethylate methylmercury; this finding is remarkable, as the canonical organomercurial lyase does not exist in these methanotrophs, indicating that a novel mechanism is involved in methylmercury demethylation. Here, we review recent findings on methanotrophic interactions with metals, with a particular focus on these metal switches and the mechanisms used by methanotrophs to bind and sequester metals.

Uptake and effect of rare earth elements on gene expression in Methylosinus trichosporium OB3b

It is well known that Methylosinus trichosporium OB3b has two forms of methane monooxygenase (MMO) responsible for the initial conversion of methane to methanol, a cytoplasmic (soluble) methane monooxygenase and a membrane-associated (particulate) methane monooxygenase, and that copper strongly regulates expression of these alternative forms of MMO. More recently, it has been discovered that M. trichosporium OB3b has multiple types of the methanol dehydrogenase (MeDH), i.e. the Mxa-type MeDH (Mxa-MeDH) and Xox-type MeDH (Xox-MeDH), and the expression of these two forms is regulated by the availability of the rare earth element (REE), cerium. Here, we extend these studies and show that lanthanum, praseodymium, neodymium and samarium also regulate expression of alternative forms of MeDH. The effect of these REEs on MeDH expression, however, was only observed in the absence of copper. Further, a mutant of M. trichosporium OB3b, where the Mxa-MeDH was knocked out, was able to grow in the presence of lanthanum, praseodymium and neodymium, but was not able to grow in the presence of samarium. Collectively, these data suggest that multiple levels of gene regulation by metals exist in M. trichosporium OB3b, but that copper overrides the effect of other metals by an as yet unknown mechanism.

Microbes and metals: interactions in the environment

Research on the behaviour of microorganisms in geogenic or anthropogenic metallomorphic environments is an integral part of geomicrobiology. The investigation of microbial impact on the fate of minerals and geologically significant compounds of mining areas can lead to an understanding of biogeochemical cycles. Metabolic processes of microorganisms are the cause for the dissolution of minerals, and especially pyrite oxidation results in the generation of acid mine drainage which, in turn, leads to heavy metal contamination as a result of mining activities. On the other hand, microbial metabolism can also contribute to the formation of certain ore deposits over geological time. The adaptation to heavy metal rich environments is resulting in microorgansims which show activities for biosorption, bioprecipitation, extracellular sequestration, transport mechanisms, and/or chelation. Such resistance mechanisms are the basis for the use of microorganisms in bioremediation approaches. As only a small part of the worldwide occurring prokaryotes has been described yet, the understanding of the role bacteria play in a geogenic and pedogenic context is very likely to change deeply as soon as more habitat relevant microbial functions can be described. Examples for the identification of microbial processes from case studies may help to advance this field. The strongly interdisciplinary field of bio-geo-interactions spanning from the microorganism to the mineral holds much promise for future developments in both basic research as well as applied sciences.

Comparative characterization of reticular and duodenal digesta and possibilities of estimating microbial outflow from the rumen based on reticular sampling in dairy cows

The objective of this experiment was to investigate the possibility of estimating the outflow of nutrients and microbial protein from the rumen based on sampling reticular contents as an alternative to duodenal sampling. Microbial protein flow estimates were also compared with a third method based on sampling of ruminal contents. Reticular and duodenal digesta and ruminal contents were recovered from 4 cows used in a 4 x 4 Latin square design experiment, in which the ruminal effects of 4 exogenous enzyme preparations were studied. Large and small particulate and fluid markers were used to estimate digesta flow in a triple-marker model; 15N was used as a microbial marker. Reticular and duodenal digesta were segregated into small and large particles (SP and LP, respectively) and a fluid phase, and ruminal digesta was segregated into particulate and fluid phases. Compared with digesta recovered at the duodenum, reticular digesta had lower OM and greater NDF contents. The proportion of microbial N was notably greater in the fluid phase of reticular digesta. Ruminal outflow of DM and OM was greater (by 17 and 28%) and that of NDF was lower (by 14%) when estimated from duodenal compared with reticular samples. There was no difference in the estimated flow of starch and nonammonia and microbial N between the reticular and duodenal techniques. Microbial N flow estimated based on ruminal sampling was similar to those based on duodenal and reticular sampling. The ruminal method, however, grossly overestimated flow of DM, OM, and NDF. This study supports the concept that microbial protein outflow from the rumen can be measured based on sampling of ruminal or reticular digesta. The reticular sampling technique can also provide reliable estimates for ruminal digestibility of OM, N, and fiber fractions. These findings need to be confirmed in experiments with basal diets varying in structure and forage-to-concentrate ratios.

Composition and digestive tract retention time of ruminal particles with functional specific gravity greater or less than 1.021

The objective of this study was to determine composition, particle size distribution, and in vivo kinetics of ruminal particles having functional specific gravity (FSG) greater or less than FSG of particles found in the omasum and reticulum of lactating dairy cows. Particles from the reticulum and the omasal had FSG of 1.03 and 1.02, respectively. Particles from ruminal contents with FSG higher (HP) or lower (LP) than 1.02 were isolated and labeled with Er or Dy, respectively. Four ruminally cannulated, lactating Ayrshire dairy cows were fed all-grass silage (AS) or 54% grass silage:46% concentrate (SC) diets in a cross-over design trial and used to study chemical composition and ruminal and total tract kinetics of HP and LP. Labeled particles were pulse dosed into the rumen of the cows and disappearance of the markers from ruminal HP and LP pools and excretion in feces was monitored for 72 and 120 h, respectively. Fecal marker excretion data were fitted using two-compartment mathematical age-dependent/age-independent (Gn-->G1) models. Inclusion of concentrate in the diet (SC) increased (P < 0.05) apparent total tract digestibility of dietary DM, OM and N. Digestibility of fiber fractions, NDF and ADF, was lower (P < 0.01 and P < 0.05, respectively) for SC compared with AS. The heavy particles had higher (P < 0.01) indigestible NDF and lower (P < 0.01) N concentration than LP. Particles from the HP pool passed from the rumen more rapidly (P < 0.01) than particles from LP (0.044 and 0.019 h(-1), respectively). Diet had no effect on particle rate of disappearance or pool size in the rumen. Across diets, pool size of LP was consistently larger (P < 0.05) than that of HP. Diet had no effect on total tract mean retention time (MRT) of LP or HP. Total tract MRT of LP was greater (P < 0.05) than MRT of HP (59.6 vs. 49.0 h, respectively). Results from this study support the hypothesis that functional specific gravity is an important factor determining the rate of outflow and residence time of feed particles within the reticulo-rumen and total digestive tract. Our data indicate that digesta particles with functional specific gravity greater or less than 1.02 have different composition and flow characteristics. Heavier particles contain more indigestible fiber and less N and are likely depleted of substrate available for microbial fermentation, are smaller in size, and have a higher passage rate/shorter retention time in the digestive tract than lighter particles.

Effects of the rare earth cerium on Escherichia coli

The rare earth cerium was found to bind rapidly to Escherichia coli. Cerium inhibited oxygen uptake in the presence of glucose as well as the endogenous respiration of glucose-grown cells. For a cell concentration of 4 mg per ml, maximal inhibition was obtained at 120 mug per ml. Greater concentrations did not increase the inhibitory effect. Cerium inhibited (14)CO(2) evolution and (14)C uptake from uniformly labeled glucose. Marked changes in the distribution of (14)C incorporated into different chemical fractions of the cell were noted. The most striking changes occurred in the alcohol- and alcohol ether-soluble fractions, in which the (14)C activity was increased 5- to 20-fold in the presence of cerium.