Bioleaching of copper- and zinc-bearing ore using consortia of indigenous iron-oxidizing bacteria

Indigenous iron-oxidizing bacteria were isolated on modified selective 9KFe(2+) medium from Baiyin copper mine stope, China. Three distinct acidophilic bacteria were isolated and identified by analyzing the sequences of 16S rRNA gene. Based on published sequences of 16S rRNA gene in the GenBank, a phylogenetic tree was constructed. The sequence of isolate WG101 showed 99% homology with Acidithiobacillus ferrooxidans strain AS2. Isolate WG102 exhibited 98% similarity with Leptospirillum ferriphilum strain YSK. Similarly, isolate WG103 showed 98% similarity with Leptospirillum ferrooxidans strain L15. Furthermore, the biotechnological potential of these isolates in consortia form was evaluated to recover copper and zinc from their ore. Under optimized conditions, 77.68 +/- 3.55% of copper and 70.58 +/- 3.77% of zinc were dissolved. During the bioleaching process, analytical study of pH and oxidation-reduction potential fluctuations were monitored that reflected efficient activity of the bacterial consortia. The FTIR analysis confirmed the variation in bands after treatment with consortia. The impact of consortia on iron speciation within bioleached ore was analyzed using Mossbauer spectroscopy and clear changes in iron speciation was reported. The use of indigenous bacterial consortia is more efficient compared to pure inoculum. This study provided the basic essential conditions for further upscaling bioleaching application for metal extraction.</p

Martian life detection with amino acid enantiomers

The Viking mission showed that Martian soil can degrade a heterotrophic medium to carbon dioxide as if live microorganisms were present. The result is considered inconclusive, however, because abiotic oxidants, such as superoxides, may also exist on Mars and would explain the Viking result. One way to resolve this ambiguity is to repeat the Viking experiment with a isomerically pure medium. The consumption of one isomer, either D or L, would indicate biological activity. Indiscriminate destruction of both isomers would indicate abiotic redox processes. This idea was validated for glucose by REU research last summer (Sun et al. 2009). The objective of this project is to test this idea with amino acids. Specifically, the consumption rates of D- and Lenantiomers will be compared for histidine, lysine, and serine in selected bacteria, archaea, and eukaryotic fungi and yeasts. Results with Bacillus revealed that in histidine, only the L-isomer was consumed while for serine and lysine, both the D- and L-isomers were utilized. If confirmed in other microorganisms, these results indicate that histidine is a suitable substrate for Martian life detection but serine and lysine are not

Plant Phenotypic Traits Eventually Shape Its Microbiota: A Common Garden Test

Plant genotype drives the development of plant phenotypes and the assembly of plant microbiota. The potential influence of the plant phenotypic characters on its microbiota is not well characterized and the co-occurrence interrelations for specific microbial taxa and plant phenotypic characters are poorly understood. We established a common garden experiment, which quantifies prokaryotic and fungal communities in the phyllosphere and rhizosphere of six spruce (Picea spp.) tree species, through Illumina amplicon sequencing. We tested for relationships between bacterial/archaeal and fungal communities and for the phenotypic characters of their plant hosts. Host phenotypic characters including leaf length, leaf water content, leaf water storage capacity, leaf dry mass per area, leaf nitrogen content, leaf phosphorous content, leaf potassium content, leaf δ13C values, stomatal conductance, net photosynthetic rate, intercellular carbon dioxide concentration, and transpiration rate were significantly correlated with the diversity and composition of the bacterial/archaeal and fungal communities. These correlations between plant microbiota and suites of host plant phenotypic characters suggest that plant genotype shape its microbiota by driving the development of plant phenotypes. This will advance our understanding of plant-microbe associations and the drivers of variation in plant and ecosystem function

Microbial consumption dynamics of amino acids (L-enantiomers: open symbol; D-enantiomers: filled symbol) by a Mojave Desert soil.

<p>Amino acids were added under four different conditions: A) first injections containing L- or D-enantiomers; B) and C) second injections containing L- or D- enantiomers; D) second injections containing racemic mixtures; and E) first injections containing L- or D-enantiomers and 25 mM of rifampicin, an antibiotic that inhibits RNA synthesis. For bacteria to catabolize D-enantiomers two conditions must be met: 1) racemases are induced if not already present due to anabolic functions, e.g. alanine racemase, and 2) L-enantiomers are exhausted.</p

Consumption dynamics of L- (open symbol) and D-aspartic acid (filled symbol) by bacterium <i>Arthrobacter</i> sp.

<p>when they were added separately and in a racemic mixture.</p

Racemization in Reverse: Evidence that D-Amino Acid Toxicity on Earth Is Controlled by Bacteria with Racemases

<div><p>D-amino acids are toxic for life on Earth. Yet, they form constantly due to geochemical racemization and bacterial growth (the cell walls of which contain D-amino acids), raising the fundamental question of how they ultimately are recycled. This study provides evidence that bacteria use D-amino acids as a source of nitrogen by running enzymatic racemization in reverse. Consequently, when soils are inundated with racemic amino acids, resident bacteria consume D- as well as L-enantiomers, either simultaneously or sequentially depending on the level of their racemase activity. Bacteria thus protect life on Earth by keeping environments D-amino acid free.</p></div

Model-predicted bacterial consumption dynamics of racemic amino acids.

<p>Three scenarios occur depending on relative racemase activity: I) the capacity of racemase exceeds that of permease (i.e. <i>V_{R max}</i> ><i>V_{L max}</i>); II) the capacity of racemase is equal to or less than that of permease but greater than the excess permeation capacity above the rate of assimilation (i.e. <i>V_{L max}</i> ≥ <i>V_{R max}</i> > <i>V_{L max}</i> –<i>V_{a max}</i>); and III) the capacity of racemase is less than the excess permeation capacity (i.e. <i>V_{R max}</i> < <i>V_{L max}</i> –<i>V_{a max}</i>).</p

Microbial consumption dynamics of racemic amino acids (L-enantiomers: open symbol; D-enantiomers: filled symbol) following addition to soils.

<p>The rapid absorption of D-enantiomers is presumably by bacteria, which possess amino acid racemases and can turn D-enantiomers into L-forms.</p

Bacterial Diversity and Community Composition Distribution in Cold-Desert Habitats of Qinghai–Tibet Plateau, China

Bacterial communities in cold-desert habitats play an important ecological role. However, the variation in bacterial diversity and community composition of the cold-desert ecosystem in Qinghai&ndash;Tibet Plateau remains unknown. To fill this scientific gape, Illumina MiSeq sequencing was performed on 15 soil samples collected from different cold-desert habitats, including human-disturbed, vegetation coverage, desert land, and sand dune. The abundance-based coverage estimator, Shannon, and Chao indices showed that the bacterial diversity and abundance of the cold-desert were high. A significant variation reported in the bacterial diversity and community composition across the study area. Proteobacteria accounted for the largest proportion (12.4&ndash;55.7%) of all sequences, followed by Actinobacteria (9.2&ndash;39.7%), Bacteroidetes (1.8&ndash;21.5%), and Chloroflexi (2.7&ndash;12.6%). Furthermore, unclassified genera dominated in human-disturbed habitats. The community profiles of GeErMu, HongLiangHe, and CuoNaHu sites were different and metagenomic biomarkers were higher (22) in CuoNaHu sites. Among the soil physicochemical variables, the total nitrogen and electric conductivity significantly influenced the bacterial community structure. In conclusion, this study provides information regarding variation in diversity and composition of bacterial communities and elucidates the association between bacterial community structures and soil physicochemical variables in cold-desert habitats of Qinghai&ndash;Tibet Plateau

The diversity and biogeography of the communities of Actinobacteria in the forelands of glaciers at a continental scale

Glacier forelands, where the initially exposed area is unvegetated with minimal human influence, are an ideal place for research on the distributions and biogeography of microbial communities. Actinobacteria produce many bioactive substances and have important roles in soil development and biogeochemical cycling. However, little is known about the distribution and biogeography of Actinobacteria in glacier forelands. Therefore, we investigated the patterns of diversity and the biogeography of actinobacterial communities of the inhabited forefields of 5 glaciers in China. Of the bacteria, the mean relative abundance of Actinobacteria was 13.1%, and 6 classes were identified in the phylum Actinobacteria. The dominant class was Actinobacteria (57%), which was followed in abundance by Acidimicrobiia (19%) and Thermoleophilia (19%). When combined, the relative abundance of the other three classes, the MB-A2-108, Nitriliruptoria and Rubrobacteria, was only 2.4%. A biogeographic pattern in the forelands of the 5 glaciers in China was not detected for actinobacterial communities. Compared with 7 other actinobacterial communities found in the forelands of glaciers globally, those in the Southern Hemisphere were significantly different from those in the Northern Hemisphere. Moreover, the communities were significantly different on the separate continents of the Northern Hemisphere. The dissimilarity of the actinobacterial communities increased with geographic distance ( r = 0.428, p = 0.0003). Because of environmental factors, the effect of geography was clear when the distance exceeded a certain continent-level threshold. With the analysis of indicator species, we found that each genus had a geographic characteristic, which could explain why the communities with greater diversity were more strongly affected by biogeography