Towards the Biobeneficiation of PGMs: Reviewing the Opportunities

Conventional beneficiation of the Platinum Group of Metals (PGMs) relies on the use of inorganic chemicals. With the depreciation of high grade deposits, these conventional processes are becoming less economically viable. Furthermore, the use of chemicals has serious negative impacts on the environment. To address the challenges of conventional PGM beneficiation, biobeneficiation has been proposed. In conventional flotation, the flotation behavior of the associated sulphides determines overall PGM recovery. The same principle may also be applied for the bio-beneficiation of PGMs. Therefore, this paper discusses the biobeneficiation behavior of sulphides closely associated with PGMs with the aim of postulating the bio-beneficiation behavior of PGMs associated with the same base metal sulphides. Conventional PGM processes are briefly discussed, as bio-beneficiation of PGMs is governed by similar underlying principles. Potential microorganisms for the biobeneficiation of PGMs are highlighted, as well as the corresponding conditions for their effectiveness. The use of both single cultures and mixed cultures is discussed. Depending on conditions, PGMs associated with pyrite and/or chalcopyrite were projected to be biofloatable with B. polymyxa, P. polymyxa, A. ferrooxidans, L. ferrooxidans, B. pumilus, B. subtilis, halophilic bacteria, Alicyclobacillus ferrooxidans, sulphate reducing bacteria, and mixed cultures of A. ferrooxidans, A. thiooxidans and L. ferrooxidans. Pyrite-associated PGMsare expected to be generally prone to biodepression, whereas chalcopyrite-associated PGMs are expected to be generally recovered as the floatable phase. Sulphate-reducing bacteria were reported to have a dual role on the bioflotation of sulphide ores (flotation and depression), depending on the conditions. Therefore, this type of microorganism may serve as both a depressant or a collector in the recovery of PGMs. Based on the bioflotation response of pyrrhotite to L. ferrooxidans, it is anticipated that pyrrhotite-associated PGMS can be biodepressed using L. ferrooxidans. In terms of bioflocculation, PGMs associated with chalcopyrite may be recovered using L. ferrooxidans, whereas A. ferrooxidans, A. thiooxidans, B. polyxyma and B. subtilis can be used in the bioflocculation of pyrite-associated PGMs. M. phlei can be employed in the reverse bioflocculation of pyrite-associated PGMs. Although no information was found on the biobeneficiation of pentlandite, postulations were made based on other sulphide minerals. It was postulated that biobeneficiation (biodepression and bioflotation) with pentlandite-associated PGMs should be possible using A. ferrooxidans. It is also projected that sulphate-reducing bacteria will be suitable for the bioflotation of PGMs associated with pentlandite. The removal of gangue species such as silicates and chromites associated with PGM concentrates was also discussed. A. ferrooxidans, P. polymyxa and B. mucilaginous are candidates for the removal of gangue species. Furthermore, the need to control process conditions was highlighted. The most suitable conditions for biobeneficiation of the various base metal sulphide minerals associated with PGMs are presented in the paper. Most of the challenges associated with biobeneficiation of PGMs are already common to conventional methods, and the means of circumventing them are already well established. Developments in genetic engineering and the advent of new data science techniques are tools that could make the biobeneficiation of PGMs a possibility.

Species Composition and Susceptibility to Antibiotics of Microorganisms Isolated from Tooth Sockets of Extracted Teeth in Cases of Alveolar Osteitis

Alveolar osteitis (AO) is one of the most common infectious complications after dental extractions. The data on the species composition of AO pathogens and their susceptibility to antimicrobial drugs can be the basis for their empirical use in case of inflammatory process aggravation. Objective. To determine the species composition and susceptibility to the antimicrobial agents of microorganisms, which were detected in patients with AO, who sought medical help in the oral surgery department of the dental medical center of Bogomolets National Medical University. Methods. Throughout 2018–2021, microbiological examination of tooth sockets from 30 patients with AO and 20 patients without AO was performed. The studied biological material was plated on appropriate nutrient media for isolation of aerobic, facultative and obligate-anaerobic microorganisms. Anaerobic conditions were achieved in GENbox 7.0 L and GENbox 2.5 L aerostats using GENbox anaerobic packages (“Biomerieux”, France). The genus and species identity of the bacteria were determined according to Bergey. Antibiotic susceptibility of the isolated strains was determined by disk diffusion method. Results. It was found that most commonly microorganisms from tooth sockets in case of AO are: Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus spp., Escherichia coli, Bacteroides spp., Clostridium spp., and Candida species, as well as their mixed cultures of 3–5 species of microorganisms. These aerobic and facultative anaerobic bacteria were susceptible to amoxicillin, ceftriaxone and ciprofloxacin in 92.6–100% of cases. The growth of anaerobic bacteria in 100% of cases was inhibited by colistin and meropenem. Conclusions. AO developing is caused by pathological colonization of socket of the extracted tooth by representatives of endogenous microbiota, namely Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus spp., Escherichia coli, which are present mainly in the mixed cultures with Candida albicans. For empirical antibiotic therapy of complicated forms of AO, amoxicillin or ceftriaxone or ciprofloxacin in complex with colistin or meropenem should be used, since these drugs suppress the growth of 92.6–100% of strains of aerobic, facultative and obligate anaerobic microorganisms, which are potential pathogens of the purulent forms of AO.

Molecular and Functional Characterization of Caveolae in Mixed Cultures of Human NT-2 Neurons and Astrocytes

Caveolae are plasma membrane invaginations that are enriched in cholesterol-binding proteins called caveolins. The presence of caveolae and caveolins in mixed cultures of human neurons and glia has not been investigated. Here, we sought to determine the presence of caveolae and caveolins in human NTera-2 (NT2/D1) cells, differentiated with retinoic acid into neuron-like (NT2/N) and astrocyte-like (NT2/A) cells. We found that while caveolin-3 mRNA levels remained relatively constant, caveolin-1 and -2 levels were upregulated in NT2/A and downregulated in NT2/N. No caveolin-1 immunoreactivity was detected in NT2/N. Electron microscopy revealed numerous flask-shaped invaginations (~86–102 nm in diameter) in the plasma membrane of NT2/A and NT2/N cells, while only few were detected in NT2/D1 cells. Immunoelectron microscopy localized caveolin-1 gold particles in the flask-shaped structures on plasmalemma and cytoplasmic vesicles of NT2/A cells. Furthermore, NT2/A endocytosed Alexa 488 conjugated-cholera toxin B subunit (CTX-B) through a caveolae- and clathrin-dependent pathway, whereas NT2/N endocytosed CTX-B through a caveolae-independent pathway. We have established that while NT2/A expressed functional caveolae, the molecular identity of the plasma membrane invaginations in NT2/N is unknown. The expression of caveolin proteins was differentially regulated in these cells. Taken together, our findings support the usefulness of the human NT2 model system to study the role of caveolins in neuron–glia communication, and their involvement in brain health and disease.

The effects of Pinus brutia bark extract on pure and mixed continuous cultures of rumen bacteria and archaea, and fermentation characteristics in vitro

The aim of the study was to investigate the effects of Pinus brutia bark extract, which is rich in polyphenolic compounds of tannins, on both pure and mixed continuous cultures of rumen bacteria and archaea, as well as on rumen fermentation characteristics in vitro. Antimicrobial susceptibility assay with pure cultures was carried out in an anaerobic chamber. Pinus brutia bark extract exhibited a potential inhibitor activity (P<0.05) against pure cultures of Ruminococcus flavefaciens, Eubacterium ruminantium, and Methanobacterium formicicum while a growth stimulatory effect (P<0.05) was observed for Ruminoccocus albus, Butyrivibrio fibrisolvens, and Streptococcus bovis. Pinus brutia bark extract only had a potential inhibitor effect (P<0.05) on R. albus at the highest dose (1200 µg/mL). Pinus brutia bark extract also stimulated (P<0.05) the growth of pure cultures of Fibrobacter succinogenes, while it did not affect Megasphaera elsdenii, except at the highest dose. The effects of two doses (75 and 375 mg/L) of P. brutia bark extract on in vitro mixed cultures and rumen fermentation parameters were determined by the rumen simulation technique (Rusitec). Supplementation with P. brutia bark extract led to a quadratic decrease (P<0.05) in the cell numbers of R. flavefaciens. Production of total and individual short chain fatty acids (SCFA), acetate to propionate ratio (C2/C3), total protozoa, ruminal pH, and dry matter digestibility (DMD) did not change in the presence of P. brutia bark extract. Supplementation with both doses of P. brutia bark extract decreased (P<0.05) the ammonia-N concentrations. Ammonia-N concentration was lowest in the high-supplemented group (P<0.05). As a conclusion, inhibitory effects of P. brutia bark extract on some species in the pure cultures were in the same direction as with mixed ruminal cultures, while stimulatory effects disappeared. The lack of inhibitory effects on protozoa and on a large number of Gram-positive rumen bacteria in the mixed cultures suggests that its mechanism of action is not exactly similar to antibiotics. Although P. brutia bark extract did not alter ruminal SCFA, it could have potential to improve ruminal protein utilization without depressing rumen microbial fermentation.

Flow-FISH as a Tool for Studying Bacteria, Fungi and Viruses

Many techniques are currently in use to study microbes. These can be aimed at detecting, identifying, and characterizing bacterial, fungal, and viral species. One technique that is suitable for high-throughput analysis is flow cytometry-based fluorescence in situ hybridization, or Flow-FISH. This technique employs (fluorescently labeled) probes directed against DNA or (m)RNA, for instance targeting a gene or microorganism of interest and provides information on a single-cell level. Furthermore, by combining Flow-FISH with antibody-based protein detection, proteins of interest can be measured simultaneously with genetic material. Additionally, depending on the type of Flow-FISH assay, Flow-FISH can also be multiplexed, allowing for the simultaneous measurement of multiple gene targets and/or microorganisms. Together, this allows for, e.g., single-cell gene expression analysis or identification of (sub)strains in mixed cultures. Flow-FISH has been used in mammalian cells but has also been extensively employed to study diverse microbial species. Here, the use of Flow-FISH for studying microorganisms is reviewed. Specifically, the detection of (intracellular) pathogens, studying microorganism biology and disease pathogenesis, and identification of bacterial, fungal, and viral strains in mixed cultures is discussed, with a particular focus on the viruses EBV, HIV-1, and SARS-CoV-2.

On some features of the cultivation of Obermeier spirochetes

After the discovery by Schaudin, in 1905, of the causative agent of syphilis, naturally keen interest among bacteriologists raised the question of the cultivation of this spirochete. However, the difficulties that were encountered on the way of the first researchers (Kolpino and Fontana, Levaditi and Mc Intosh, Schereschewsk y, Hoffmann) in solving this problem forced the question of cultivating spirochetes in general to be put on the agenda. Therefore, it is not a mere coincidence that the first pure culture of the spirochete (Spir. Dentium) was obtained by Mhlen S'OM in 1906, that is, already a year after the discovery of the pale spirochete. However, mixed cultures of spirochetes (so-called Mischkultur) were obtained even earlier Goadby B1903, Veszpmi, Walver and F unni with lif fʹ, Mll e r and Scherber in 1905. In 1909, Schereschewsky received a pale spirochete in a culture mixed with other bacteria, and in the same year, Mhlens, and a year later, Hoffmann announced that they had received a pure culture of this spirochete.

Studi Literatur: Aplikasi dan Fungsi Porang (Amorphophallus Oncophyllus) dalam Frozen Yoghurt

— Frozen yoghurt is a frozen desserts made with yoghurt and quite similar to ice cream but low in calorie, which cointains milk, sweetener, stabilizers, emulsifier, and lactic acid bacteria (LAB) cultures through combination of process freezing and agitation. The optimal pH about 5.5 on LAB growth and the use of different strains of LAB culture or LAB mixed cultures that can maintain the viability of LAB during processing and freezing storage of frozen yoghurt. The use of LAB mixed cultures could improve viscos ity and overrun of frozen yogurt. The viability of the LAB cultures remained above minimal limit of 107CFU/g in frozen yogurt due to the viability of LAB decrease significantly during processing and freezing storage , high viable survival rate during delivery through the gastrointestinal tract higher than 106CFU/g. The issues that often arise relates to frozen yogurt processing are a grainy texture, faster melting rate and the low viscosity and overrun value. Addition of porang flour in frozen Yogurt as stabilizer and emulsifier that has an extremely high water-holding capacity, which is able to bind water 200 times its molecular weight due to its high solubility, porang glucomannan gel formed in freezing process which can improve the quality of organoleptic having the better consistency and texture of frozen yoghurt. The use of different concentration of porang flour which can have different result in the final gel formed, have complex effects on viscosity, overrun, melting rate, pH, titratable acidity (TA), total LAB and decrease the ability proteolysis of LAB in frozen yoghurt. Keywords: frozen yoghurt, porang, viability Abstrak— Frozen yoghurt merupakan jenis dari makanan penutup seperti es krim yang dibuat menggunakan yoghurt sebagai bahan utama yang terdiri dari susu, bahan pemanis, stabilisator, pengemulsi, dan kultur BAL melalui kombinasi proses pembekuan dan agitasi. pH optimal diantara 5.5 mendukung pertumbuhan BAL dengan baik dan penggunaan kultur BAL strain yang berbeda maupun kultur BAL kombinasi dalam upaya mempertahankan viabilitas BAL selama proses pembuatan dan pembekuan frozen yoghurt. Penggunaan kultur BAL kombinasi juga meningkatkan viskositas dan overrun frozen yoghurt. Persyaratan jumlah BAL minimal 107CFU/g dalam pembuatan frozen yoghurt karena adanya penurunan viabilitas BAL selama produksi berlangsung dan penyimpanan beku frozen yoghurt, serta syarat jumlah bakteri hidup yang sampai di saluran pencernaan harus lebih dari 106CFU/g. Permasalahan yang sering timbul pada proses pembuatan frozen yoghurt adalah tekstur yang tidak lembut, viskositas yang rendah, kecepatan meleleh yang cepat, dan overrun rendah. Adanya penambahan tepung porang dalam frozen yoghurt sekaligus sebagai stabilisator dan pengemulsi yang mengikat molekul air dalam jumlah besar, yakni hingga 200 kali lipat berat molekulnya karena kelarutannya yang tinggi, sehingga membentuk gel porang glukomannan pada saat pembekuan yang dapat meningkatkan mutu organoleptik dengan memiliki tekstur yang lebih baik pada frozen yoghurt. Penggunaan konsentrasi tepung porang yang berbeda, pembentukan gel yang dihasilkan juga berbeda dan terdapat pengaruh terhadap viskositas, overrun, kecepatan meleleh, pH, asam tertitrasi, total BAL dan menurunkan kemampuan proteolisis BAL pada frozen yoghurt. Kata kunci: frozen yoghurt, porang, viabilitas