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The present study is related to elucidating the remote sensing monitoring and capabilities for profiling to particulate matter (PM) mass concentration control in the lowest atmospheric layers. The PM was studied at a distance of 5.5 km from the LIDAR station. The experiments were conducted in May and October 2020 in the South-Eastern part of the Bulgarian capital Sofia during a COVID-19 lockdown. The LIDAR measurement data was compared during the experiments with in situ sampling by mobile devices located just below the spot of the LIDAR beam: (i) Absorber collects particles higher thеn 3 µm; (ii) PM Microcollector type SDS 011; and (iii) Andersen Cascade Impactor for exploring PM size distribution and microbiota. The results obtained show that remote sensing can be very effective when quantitative evaluation has been combined with in situ sampling for PM qualitative assessment. more...

The object of this study is a biogenic material obtained from neutrophilic sheath-forming iron bacteria of the genus Leptothrix cultivated in a specific medium. Light microscopy and scanning electron microscopy were used to characterize the biogenic product. The X-ray diffraction spectrum of the control sample (without inoculated bacteria) is presented to demonstrate the important role of the bacteria in the Fe2+ transformation. Unlike the biogenic product, where nanoparticles of lepidocrocite are present, no traces of stable single-phase iron oxide or oxyhydroxide were detected in the control sample. The study of the biogenic sample showed a lack of significant differences between the naturally obtained and the artificially produced sheaths. Magnetostriction effect measurements were conducted to probe how the different magnetic behavior at temperatures below and above the Neel temperature (50 - 77 K) could be used in possible applications of the material in actuating and sensing devices. more...

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The main problem of the direct molecular approaches for studying environmental samples is the so called preferential PCR amplification which can mask the presence of some DNA templates in the samples. For this reason the application of the classical approach of the enrichment cultures, in parallel to the molecular retrievals, for studies on bacterial diversity in the environment may be helpful. Of course, here the limitation to analyze only those strains of the community which are able to grow individually exists. It is a compromise to analyze enriched biofilm cultures or mixed cultures instead of pure cultures, because most of the bacteria in the extreme environments are living in consortia which are described as symbiotic [1, 2]. The identification of the members of such mixed cultures using the 16S rDNA retrieval may provide very important information in addition to those, derived by the direct methods, about the bacteria present in the samples studied. Our studies on phylogenetic diversity of bacteria cultured as pure and/or mixed cultures from the uranium wastes are presented in Table 1. From these results one can see that bacterial strains known for their ability to biotransform metals were recovered from the samples. For example, different types of Acidithiobacillus ferrooxidans, which are oxidizing iron and sulfur compounds and Leptospirillum ferrooxidans , oxidizing iron, were cultured. These two groups of bacteria play a significant role in the mobilization of many metals and radionuclides in the wastes, because as a result of their physiological activity large amounts of H2SO4 are produced and the pH in their surrounding is extremely low. Individual cultures representing sulfate reducing bacteria of the genus Desulfovibrio which are able to reduce also uranium and other metals were cultured from the uranium mining waste samples as well. In addition, strains belonging to the species Pseudomonas stutzeri, Pseudomonas migulae, Erwinia herbicola (g-Proteobacteria) as well as isolates related to Agrobacterium and Sphingomonas (a-Proteobacteria) were cultured. In addition to the above described individual bacterial isolates several enrichment mixed cultures were recovered. One of them, called initially "JG1", from which the sulfate reducing Desulfovibrio isolate JG1 was purified, consisted of 11 diverse representatives of Clostridium (see the series of clones IrT-JG1 affiliated to the Bacillus/Clostridium group in Table 1) and the two clones IrT-JG1-58 and IrT-JG1-71 closely related to the isolate Desulfovibrio JG1. Formerly we have reported that the mixed culture of "JG1" is able to reduce and precipitate amounts of about 1.5 g of U(VI) per g of dry weight bacterial biomass from a liquid medium independently on its pH value in the range between 2.8 and 6.0 [3]. Our recent results demonstrated, however, that the U(VI) reducing capacity of the pure culture of Desulfovibrio sp. JG1 does not differ significantly from those published for the other uranium reducing bacteria, Desulfovibrio vulgaris, D. desulfuricans, and Geobacter metallireducens which is about five times lower and, in addition, it is pH dependent with an optimum of pH 6.8 [4, 5]. This indicates that the higher capability of the mixed culture "JG1" to precipitate uranium at a wider range of environmental conditions (pH for example) is a result of the combined function of the different bacterial members of which it consists. We suppose that in addition to the U(VI) reduction performed by the above mentioned natural strains of Desulfovibrio sp. (JG1, IrT-JG1-58 and JrT-JG1-71) some other processes occur, as bio-precipitation or/and bio-minearalisation stimulated by the metabolic functions of the described Clostridia present in the mixed culture. Another mixed culture "JG14" consisted of different a-Proteobacteria (Agrobacterium and Rhizobium) and a microdiverse population of environmental strains of Stenotrophomonas maltopilia (d-Proteobacteria). ... more...

A large number of acidophilic chemolithoautotrophic iron oxidizing bacterial isolates recovered from two uranium mining waste piles was classified as Leptospirillum ferrooxidans. For this purpose a combination of classical and molecular microbiological methods was applied. The letter involved Amplified Ribosomal DNA Restriction Endonucleases analysis (ARDREA) and 16S rDNA sequence analysis. In the ARDREA two sets of primers were involved: one universal -16S7f and 16S1406r, and one species specific -16S176f and 16S679r (De-Wulf-Durand et al,.1997, Tzvetkova et al., 1999). In both cases using endonuclease RsaI, two groups were discriminated among the isolates studied. These groups correspond to the recently characterized RsaI RFLP types I and II of L. ferrooxidans, which include the type strain of the species L. ferrooxidans DSM 2705T (type I) and the strains L. ferrooxidans DSM 2391 and Lf30A (type II); (Fig.1 and Tzvetkova et. al., 1999); An additional extensive comparative sequence analysis of the variable region 3 of a series of natural isolates and the deposited sequences of this region in the EMBL allowed to distinguish seven L. ferrooxidans groups. Each group possesses a specific signature in the helix 18 of the variable region 3 (Fig.2). These signatures discriminate particular types of the species and possibly reflect the genetic adaptations of different parts of the natural L. ferrooxidans populations to different concentrations of heavy metals and other components of their natural environment. The variability of the helix 18 influences target sites of several frequently cutting endonucleases and allows discrimination of some of the above mentioned groups. The interaction of some L. ferrooxidans natural isolates with uranium was studied at different concentrations of the metal and at two pH values. Results demonstrating accumulation of U(VI) at unusually low pH values are presented and discussed in the poster more...