Solubilization Rate Research Articles

Weathering of calcareous bedrocks is strongly affected by the activity of soil microorganisms

Phosphorus (P) availability in calcareous forest soils is commonly low compared to siliceous soils. The main reason for this is that phosphate ions tend to precipitate with calcium (Ca). Weathering of calcareous rocks and the potential of microorganisms to dissolve calcareous parent material is not fully understood. Therefore, we examined microbial carbonate dissolution and the abundance of phosphorus-solubilizing bacteria in temperate forest soils with contrasting calcareous parent materials. We incubated soil extracts with weathered parent materials (i.e., dolomite and limestone) from two calcareous forest soils differing in P content and determined the rates of P and Ca solubilization. In addition, we determined the abundance of phosphorus-solubilizing bacteria (PSB). We found that the net Ca solubilization rate ranged from 8.8 to 511.1 nmol m−2 d−1 across both soils and depths. Calcium dissolution rates were negatively related to pH and positively related to the concentration of organic acids. The gross P solubilization rates were on average 63.6% higher from dolomite (P-poor soil) than from limestone (P-rich soil). The abundance of soil PSB ranged from 3.8 % at the limestone site (P-rich soil) to 24.4 % at the dolomite site (P-poor soil). The higher abundance of PSB in the soil derived from dolomite is in line with the high Ca and P solubilization rates at this site, indicating that PSB abundance is related to rock weathering rates from calcareous soils. Pseudomonadales and Enterobacteriales were by far the two most abundant bacterial orders in the PSB community of both soils and soil depths. In conclusion, this study shows, first, that weathering of calcareous bedrocks is strongly affected by the activity of soil microorganisms, and second, that there is likely a selective pressure in P-poor soils towards a higher abundance of PSB.

Bioleaching of metals from waste printed circuit boards using bacterial isolates native to abandoned gold mine.

In the present study, native bacterial strains isolated from abandoned gold mine and Chromobacterium violaceum (MTCC-2656) were applied for bioleaching of metals from waste printed circuit boards (WPCBs). Toxicity assessment and dose-response analysis of WPCBs showed EC50 values of 128.9, 98.7, and 90.8g/L for Bacillus sp. SAG3, Bacillus megaterium SAG1 and Lysinibacillus sphaericus SAG2, respectively, whereas, for C. violaceum EC50 was 83.70g/L. This indicates the viable operation range and technological feasibility of metals bioleaching from WPCBs using mine isolates. The influencing factors such as pH, pulp density, temperature, and precursor molecule (glycine) were optimized by one-factor at a time method (OFAT). The maximum metal recovery occurred at an initial pH of 9.0, a pulp density of 10g/L, a temperature of 30°C and a glycine concentration of 5g/L, except for L. sphaericus which showed optimum activity at initial pH of 8.0. Under optimal conditions the metals recovery of Cu and Au from WPCBs were recorded as 87.5 ± 8% and 73.6 ± 3% for C. violaceum and 72.7 ± 5% and 66.6 ± 6% for B. megaterium, respectively. Kinetic modeling results showed that the data was best described by first order reaction kinetics, where the rate of metal solubilization from WPCBs depended upon microbial lixiviant production. This is the first report on bioleaching of metals from e-waste using bacterial isolates from the gold mine of Solan, HP. Our study demonstrated the potential of bioleaching for resource recovery from WPCBs dust, aimed to be disposed at landfills, and its effectiveness in extraction of elements those are at high supply risk and demand.

Hydrolysis of Lignocellulosic Biomass in Hot-Compressed Water with Supercritical Carbon Dioxide.

This study investigated the decomposition behavior of bamboo under hydrothermal and hydrolysis conditions with H2O/CO2 in a semicontinuous-flow reactor at 9.8 MPa. At 255 °C, with and without CO2, xylan in bamboo completely decomposed into xylo-oligosaccharide (XOD). The yield of glucan degradation products with CO2 was significantly higher compared with that under the hydrothermal reaction (25.7 vs 14.9 wt %, respectively). The reaction rate of glucan decomposition with CO2 was slightly higher than the rate of hydrothermal reaction (kH2O/CO2/kH2O = 1.3). Increasing the fluid velocity of the hydrothermal reaction (3–10 mL/min) significantly accelerated the solubilization rate, but the ultimate yield of the soluble fraction was unchanged. The ultimate yield of the soluble fraction was slightly affected by physical effects. Hydrolysis with CO2 under severe conditions exhibited effective degradation of glucan. The catalytic activity of the H2O/CO2 system under hydrolysis can be explained by the system’s chemical effect.

Modelling of gas evolution during powder rehydration for Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS)

As a powder wets and dissolves in a liquid, trapped gas bubbles are released and the measurement of the evolution of gas volume versus time can be used to quantify the ease with which powder wets and dissolves in the liquid. This phenomenon forms the basis of the BARDS analytical measurement technique. To complement this experimental approach, a model of the evolution of gas bubbles from a powder into a liquid during powder dispersion and solubilisation is presented. The model is validated against experimental data from the rehydration of Milk Protein Isolate (MPI) powder; both in its original state, and in the agglomerated state and is shown to match the experimental data with good accuracy. Use of the model facilitates a fuller interpretation of the experimental BARDS data and the values of dispersion and solubilisation rate constants can be applied for quantitatively comparing the behaviour of powders. It also permits development of robust rehydration parameters from the experimental BARDS signal.

Chemical recycling of waste Poly Vinyl Chloride (PVC) by the liquid-phase treatment

Liquid-phase treatment of waste Poly Vinyl Chloride (PVC) was performed. Chlorine change rate was high when using alcohol, cresol and terpene compared with that observed in the treatment without solvent, so the importance of solvent for dechlorination from PVC was confirmed. By the treatment in alcohol, generation of porous structure was confirmed, which were not observed in the treatment of PVC alone. We were able to propose a method of utilizing carbon resources after chlorine is removed from a different perspective than previous reports. The number of pores and pore size were controlled by adding CO2 gas and basic compound, especially Na2CO3 in 1-Butanol. It indicated that these elements were effective for the production of porous structure based on the liquid-phase treatment. On the other hand, solubilization rate reached near 90% by using terpene at 300 °C in air atmosphere. The most effective solvent for solubilization was o-Cresol and solubilization rate reached to 99.8% at 250 °C in air atmosphere. This result indicates that PVC can be completely decomposed by these solvents in the presence of oxygen. From this research, it is possible to utilize and decompose solid residue by selecting the conditions.

Solute induced jittery motion of self-propelled droplets

The intriguing role of the presence of solutes in the activity of a self-propelling droplet is investigated. A system of self-propelling micrometer-sized 4-Cyano-4′-pentylbiphenyl (5CB) droplets in an aqueous solution of tetradecyltrimethylammonium bromide (TTAB) as the surfactant is considered. It is shown that the addition of glycerol causes the active 5CB droplet to exhibit a transition from smooth to jittery motion. The motion is found to be independent of the droplet size and the nematic state of 5CB. Analogous experiments with Polyacrylamide (PAAm), Polyvinylpyrrolidone (PVP), and Polyvinyl Alcohol (PVA), as solutes, confirm that such a transition cannot merely be explained solely based on the viscosity or Peclet number of the system. We propose that the specific nature of physicochemical interactions between the solute and the droplet interface is at the root of this transition. The experiments show that the timescales associated with the influx and redistribution of surfactants at the interface are altered in the presence of solutes. Glycerol and PVP significantly enhance the rate of solubilization of the 5CB droplets resulting in a quicker re-distribution of the adsorbed TTAB molecules on the interface, causing the droplet to momentarily stop and then restart in an independent direction. On the other hand, low solubilization rates in the presence of PAAm and PVA lead to smooth trajectories. Our hypothesis is supported by the time evolution of droplet size and interfacial velocity measurements in the presence and absence of solute. Overall, our results provide fundamental insights into the complex interactions emerging due to the presence of solutes.

The ability of some microbes to solubilize the hardly soluble phosphorous and potassium from various sources in vitro

Utilization of bio-fertilizer is an alternative option to maintain the available phosphorus (P) and potassium (K) in the soil. To develop such a bio-fertilizer, the ability of microbes to solubilize phosphate and potassium is one of the most important things. A set of experiments was conducted to evaluate the ability of some microbes (7 bacteria and 7 fungi isolates) to solubilize the hardly soluble P (Ca3PO4, AlPO4, FePO4 and Blora rock phosphate) and K (Malang feldspar) sources in vitro. The results showed that the solubilization rate of hardly soluble P and K sources by microbes are different depending on isolates type and sources applied. The amounts of P released from Ca3PO4, AlPO4, FePO4 and rock phosphate in liquid medium were significantly increased by the isolates, respectively up to 8.8, 69.3, 928, 26 times more than the control (un-inoculated). Some of them also significantly increased the solubility of the K containing mineral (feldspar), up to 2.3 times more than the control. Acidification of the medium has been observed to be the most important mechanism for the P and K solubilization, especially for Ca3PO4, AlPO4. The JK1 fungal isolate was the most promising phosphate-potassium solubilizing microbe.

Coculture with hemicellulose-fermenting microbes reverses inhibition of corn fiber solubilization by Clostridium thermocellum at elevated solids loadings

BackgroundThe cellulolytic thermophile Clostridium thermocellum is an important biocatalyst due to its ability to solubilize lignocellulosic feedstocks without the need for pretreatment or exogenous enzyme addition. At low concentrations of substrate, C. thermocellum can solubilize corn fiber > 95% in 5 days, but solubilization declines markedly at substrate concentrations higher than 20 g/L. This differs for model cellulose like Avicel, on which the maximum solubilization rate increases in proportion to substrate concentration. The goal of this study was to examine fermentation at increasing corn fiber concentrations and investigate possible reasons for declining performance.ResultsThe rate of growth of C. thermocellum on corn fiber, inferred from CipA scaffoldin levels measured by LC–MS/MS, showed very little increase with increasing solids loading. To test for inhibition, we evaluated the effects of spent broth on growth and cellulase activity. The liquids remaining after corn fiber fermentation were found to be strongly inhibitory to growth on cellobiose, a substrate that does not require cellulose hydrolysis. Additionally, the hydrolytic activity of C. thermocellum cellulase was also reduced to less-than half by adding spent broth. Noting that > 15 g/L hemicellulose oligosaccharides accumulated in the spent broth of a 40 g/L corn fiber fermentation, we tested the effect of various model carbohydrates on growth on cellobiose and Avicel. Some compounds like xylooligosaccharides caused a decline in cellulolytic activity and a reduction in the maximum solubilization rate on Avicel. However, there were no relevant model compounds that could replicate the strong inhibition by spent broth on C. thermocellum growth on cellobiose. Cocultures of C. thermocellum with hemicellulose-consuming partners—Herbinix spp. strain LL1355 and Thermoanaerobacterium thermosaccharolyticum—exhibited lower levels of unfermented hemicellulose hydrolysis products, a doubling of the maximum solubilization rate, and final solubilization increased from 67 to 93%.ConclusionsThis study documents inhibition of C. thermocellum with increasing corn fiber concentration and demonstrates inhibition of cellulase activity by xylooligosaccharides, but further work is needed to understand why growth on cellobiose was inhibited by corn fiber fermentation broth. Our results support the importance of hemicellulose-utilizing coculture partners to augment C. thermocellum in the fermentation of lignocellulosic feedstocks at high solids loading.

Recovery and liquefaction of nitrogen-containing component and minerals from food processing wastes of vinegar using subcritical water

In recent years, environmental problems such as production of industrial waste are getting worse in Japan. In particular, food processing residues are typically disposed of by spending a large amount of money. This paper studied the treatment of two by-products from vinegar production (rice bran and sake lees) using subcritical water and analyzing the extracted solution for functional ingredients. The results from sake lees showed that an operating temperature of 180 °C and a reaction time of 30 min solubilized 85% of the nitrogen-containing component (mainly protein) from the raw material into water-soluble peptides. When rice bran was used as the raw material the solubilization rate of the nitrogen-containing components was greatly decreased at a reaction temperature of 190 °C or higher. It was shown that calcium in the raw material caused the formation of water-insoluble complexes with amino acids and ammonia such as CaCN2. Subcritical water treatment was shown to be a useful technique to recover useful water-soluble components from residual solid biomass.

Impact of Fe(III) (Oxyhydr)oxides Mineralogy on Iron Solubilization and Associated Microbial Communities.

Iron-reducing bacteria (IRB) are strongly involved in Fe cycling in surface environments. Transformation of Fe and associated trace elements is strongly linked to the reactivity of various iron minerals. Mechanisms of Fe (oxyhydr)oxides bio-reduction have been mostly elucidated with pure bacterial strains belonging to Geobacter or Shewanella genera, whereas studies involving mixed IRB populations remain scarce. The present study aimed to evaluate the iron reducing rates of IRB enriched consortia originating from complex environmental samples, when grown in presence of Fe (oxyhydr)oxides of different mineralogy. The abundances of Geobacter and Shewanella were assessed in order to acquire knowledge about the abundance of these two genera in relation to the effects of mixed IRB populations on kinetic control of mineralogical Fe (oxyhydr)oxides reductive dissolution. Laboratory experiments were carried out with two freshly synthetized Fe (oxyhydr)oxides presenting contrasting specific surfaces, and two defined Fe-oxides, i.e., goethite and hematite. Three IRB consortia were enriched from environmental samples from a riverbank subjected to cyclic redox oscillations related to flooding periods (Decize, France): an unsaturated surface soil, a flooded surface soil and an aquatic sediment, with a mixture of organic compounds provided as electron donors. The consortia could all reduce iron-nitrilotriacetate acid (Fe(III)-NTA) in 1–2 days. When grown on Fe (oxyhydr)oxides, Fe solubilization rates decreased as follows: fresh Fe (oxyhydr)oxides > goethite > hematite. Based on a bacterial rrs gene fingerprinting approach (CE-SSCP), bacterial community structure in presence of Fe(III)-minerals was similar to those of the site sample communities from which they originated but differed from that of the Fe(III)-NTA enrichments. Shewanella was more abundant than Geobacter in all cultures. Its abundance was higher in presence of the most efficiently reduced Fe (oxyhydr)oxide than with other Fe(III)-minerals. Geobacter as a proportion of the total community was highest in the presence of the least easily solubilized Fe (oxyhydr)oxides. This study highlights the influence of Fe mineralogy on the abundance of Geobacter and Shewanella in relation to Fe bio-reduction kinetics in presence of a complex mixture of electron donors.

Evaluation of biohydrogen production potential of fragmented sugar industry biosludge using ultrasonication coupled with egtazic acid

In this study, the influence of ultrasonication (USN) combined with egtazic acid fragmentation method on sugar industry waste (SWS) sludge was studied for improving biohydrogen production. Initially, USN method was proceeded by varying power and fragmentation time. At an optimal power (115 W) and fragmentation time (30 min), USN method demanded 23,000 kJ/kg TS specific energy for achieving 15.2% complex organics solubilization rate (COR). To further upsurge of SWS sludge solubilization, USN assisted with egtazic acid (USNEG) method was performed by varying fragmentation time and egtazic acid dosage at an optimal power (115 W). USNEG method has achieved more COR (23%) at minimum specific energy of 11,500 kJ/kg TS (fragmentation time: 15 min and EGTA dosage: 0.03 g/g TS). Then, biohydrogen potential (BHP) assay was investigated in which USNEG method has obtained higher biohydrogen production. Also, energy analysis revealed that USNEG method exhibited an energy ratio of 1.78.

Microbial solubilization of silicon and phosphorus from bedrock in relation to abundance of phosphorus-solubilizing bacteria in temperate forest soils

Biogeochemical weathering of bedrock is the most important input of silicon (Si) and phosphorus (P) to forest ecosystems. While soil microbes, and in particular P-solubilizing bacteria (PSB), are known to accelerate the solubilization of Si and P from silicate rocks, our understanding of the mechanisms driving biogenic weathering are still limited. To fill this gap, incubation experiments with weathered parent materials (i.e. basalt, andesite and paragneiss) of four soils and water extracts of the four soils, differing in P stocks, were conducted. We found that the net Si solubilization rate ranged from 5.0 (±1.8) to 91.0 (±2.4) nmol m−2 d−1 across all examined soils. The silicate dissolution rates were negatively related to the decrease in pH (ΔpH) and positively related to the amounts of organic acids released by microbes. We found that the gross P solubilization rates from the parent materials were ~11 times higher at the P-rich site (BBR) compared to the P-poor site (CON). In addition, we determined the abundance and the taxonomic composition of PSB communities in the four soils. The abundance of PSB ranged from 2% at the P-rich site to 22.1% at the P-poor site, indicating that a selective pressure exists in P-poor soils towards a higher abundance of P-solubilizers. Yet, despite the relative high abundance of PSB, the gross P solubilization rates were low in the soils derived from P-poor parent material. The genus Pseudomonas was found only in the PSB community at the P-poor site. Burkholderiales and Bacillales together were by far the two most abundant orders among the PSB communities in all soils and depths. In conclusion, this study shows that PSB are more abundant in P-poor soil than in P-rich soil, while the weathering rate seems to be mostly dependent on the bedrock.

The Effect of Indigenous Phosphate-Solubilizing Bacteria on Quercus Brantii Seedlings Under Water Stress

ABSTRACT In the Mediterranean climate, plants, e.g., Quercus brantii Lindl, have evolved and adapted to bear up low soil-water and soil-phosphorus conditions. Quercus brantii Lindl. is a dominant tree species thorough Zagros Mediterranean forests. Phosphate-solubilizing bacteria (PSB) play crucial role in the plant growth enhancement by solubilizing insoluble soil-phosphate. In the present study, the effects of two indigenous PSB strains, e.g., Microbacterium sp. (M.) and Streptomyces sp. (S.) were individually and combined evaluated on growth and physiological traits of Quercus brantii. seedlings under different water stress treatments. Results showed that maximum P- solubilization rate was observed by M. strain. Results also revealed that water stress increased electrolyte leakage and reduced relative water content in all plant compartments as well as growth parameters. Two PSB strains individually and in combination significantly enhanced growth and physiological traits of seedlings under both irrigation treatments compared with the non-inoculated seedlings. The M. strain showed higher potential for increasing of root length, weight and RWC compare to other PSB strain. Finally, the results suggested that application of isolated indigenous PSBs in reforestation could help to cope with the drought conditions in semi-arid Mediterranean Zagros forests by increasing of root and improving of oak seedlings growth.

On-line spectroscopic study of brominated flame retardant extraction in supercritical CO2

Removal of brominated flame retardants (BFRs) from polymers before disposal or recycling will alleviate negative environmental effects and ensure safe usage of recycled products. Extraction of BFRs in supercritical CO2 is appealing but also presents challenges to industries due to limited solubility and lack of kinetic studies. For a more comprehensive evaluation of supercritical extraction potentialities, we (i) developed an on-line pressure apparatus that is compatible with both the FTIR and UV–vis spectrometers to enable kinetic and thermodynamic studies; (ii) studied kinetic extraction involving three conventional and two novel BFRs as well as three typical polymeric matrix. Solubilities were determined using the gravimetric method or X-ray fluorescence. FTIR exhibited a superior applicability compared to UV–vis in the following BFR extraction’s time-dependency binary and ternary systems. We observed that faster stirring speed, higher temperature, and finer particle size can accelerate the overall extraction kinetics. In binary systems, it took less than 2 h to achieve equilibrium for each BFR at 60 °C, 25 MPa and 1000 rpm. In the presence of polymeric matrix, slower extraction kinetics were observed due to the occurrence of competitive dissolution and molecular diffusion within the matrix. Mathematical models derived from irreversible desorption and Fick’s diffusion laws fitted well with the observed extraction kinetics of BFRs, thus enabling us to identify the rate-determining step. The high solubilization rate coefficients that we measured for BFRs revealed that the dynamic extraction process in up-scaling design could compensate for the low solubility with flowing supercritical CO2.

Phosphate-solubilizing bacteria and fungi in relation to phosphorus availability under different land uses for some latosols from Guangdong, China

Some soil bacteria and fungi are known to solubilize phosphates and play an important role in supplying phosphorus (P) to plants. In this study, we characterized the phosphate-solubilizing bacteria and fungi as well as P availability in latosols from southern China under different land use practices. Three different latosols (i.e., red soil, lateritic red soil and laterite red soil), each with four different land uses (i.e., agricultural land, grass land, forest land and orchard land), from Guangdong Province, China, were chosen to determine the amounts of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) and their phosphate solubilizing abilities. Our results show that the amount of available P (AP) increased with the amount of PSB favored in solubilizing organic P (or PSBop), while the amount of PSF increased with the content of soil organic carbon (SOC). The average rates of phosphate solubilization were 28.23% for PSBop, 6.97% for PSF, and 0.16% for PSBip (PSB favored in solubilizing inorganic P). An increase in soil pH decreased the ability of PSB to solubilize phosphate in latosols. This ability occurred in the following order: PSBop > PSF > PSBip. No significant difference in the amount of PSF was observed among the four different land uses for the lateritic red soil and laterite red soil, whereas a profound significant difference was found for the red soil, with the highest number of PSF in the grass land. Reasonable linear correlations between the PSB and the AP and between the PSF and the SOC were obtained and could provide a good reference to characterize soil PSB and PSF. Additionally, PSBop was the best bacterial species to solubilize phosphate in the latosols.

Improving heavy metals removal, dewaterability and pathogen removal of waste activated sludge using enhanced chemical leaching

In order to enhance heavy metals removal, two enhanced chemical leaching techniques were examined comparatively using NaClO and NaNO2 with the addition of FeCl3. The phosphorus release, dewaterability and pathogen removal of treated sludge were also examined after chemical leaching. The results showed that the heavy metals solubilization, improvement of dewaterability and pathogen removal were simultaneously achieved. Compared with NaClO treatment system, the better solubilization rates of Zn and Ni were observed in the NaNO2 treatment system. The improvement of Cu, Zn and Ni removal can be attributed to the disruption of the organically bound metal fraction based on metal distribution and EEM analysis. The TP loss caused by chemical leaching in this study was in the range of 47 %–54%. The treated sludge of the two systems could both meet Class A biosolids standards (US EPA) for land application. These results provided an alternative chemical leaching method for simultaneous improvement of sludge properties.

Response of soil phosphorus fractions and fluxes to different vegetation restoration types in a subtropical mountain ecosystem

Soil phosphorus (P) improvement is one of the important aims of vegetation restoration. However, the effects of different vegetation restoration types on soil P cycling and the underlying mechanisms remain unclear. Together with vegetation structure and soil properties, we measured the soil P fractions and P transformation rates to evaluate the characteristics of ecologically relevant soil P fraction distributions and their dynamics for the most common vegetation restoration types in a subtropical mountain ecosystem (i.e., PF, Pinus forest; EF, Eucalyptus forest; SL, shrubland; and NSF, natural secondary forest). We found that water-extractable inorganic P (Pi), organic P (Po), and acid phosphatase activity (APA) were significantly higher in NSF than those in the other vegetation types (P < 0.01), together with the highest gross P mineralization rate (Pmin) and net P immobilization rate (Pimm), suggesting biological processes played a more important role in soil P cycling in the NSF. In contrast, the soil showed the lowest values of Pmin, Pimm, and APA in the EF compared to NSF and PF (P < 0.05), together with the highest P loss and the higher net P solubilization rate (Psol), indicating the greater importance of soil geochemical processes. Compared with the NSF and EF, geochemical and biological processes co-regulated soil P cycling in the PF and SL. However, the soil in the PF displayed higher P fluxes (Pmin, Pimm, Psol, and P loss) than those in the SL (P < 0.05), suggesting the soil had higher P flux magnitudes in the PF. Results of correlation analyses showed that the soil microbial community structure and activity played a more important role than plant community attributes and soil physicochemical properties in soil P fraction distribution and fluxes. In conclusion, soil P fraction distributions and their fluxes can be significantly influenced by vegetation restoration types. Land management strategies focusing on restoration of the soil microbial community may enhance soil P cycling and improve soil quality.

Microbial release of apatite- and goethite-bound phosphate in acidic forest soils

Phosphorus (P) is an element crucial for plant nutrition. P can be bound in primary minerals such as apatites or to secondary minerals, such as metal(hydr-)oxides. Microorganisms are capable of releasing mineral-bound P, and thus, transforming it into plant-available forms. This study examined the potential of native microbial communities of five beech forest soils to release P either from hydroxyapatite or P-loaded goethite. Incubation experiments with soil extracts, either with or without glucose, were conducted. Desorption of phosphate from goethite was less effective than the solubilization of phosphate from hydroxyapatite. We found that the net P solubilization from hydroxyapatite was driven by the microbial production of low molecular weight organic acids (LMWOAs), such as D-gluconic and 2-keto-D-gluconic acids, and differed among the microbial communities extracted from the five forest soils. In contrast, the net P desorption rates from goethite did not vary significantly among the microbial communities extracted from the different soils. Microbial acidification of the solution increased the adsorption of phosphate to goethite, whereas less acidic conditions promoted progressive desorption of phosphate. Microbial communities in soil extracts incubated with P-loaded goethite downregulated the release of organic acids, which reduced acidification. The net P solubilization rates from hydroxyapatite and the net P desorption rates from goethite were strongly increased by the addition of glucose, suggesting that microbial P mobilization from minerals is strongly carbon limited. In conclusion, the study shows that microbial communities from acidic beech forest soils are much more efficient at releasing phosphate from hydroxyapatite than from goethite.

Low Temperature Dissolution of Yeast Chitin-Glucan Complex and Characterization of the Regenerated Polymer.

Chitin-glucan complex (CGC) is a copolymer composed of chitin and glucan moieties extracted from the cell-walls of several yeasts and fungi. Despite its proven valuable properties, that include antibacterial, antioxidant and anticancer activity, the utilization of CGC in many applications is hindered by its insolubility in water and most solvents. In this study, NaOH/urea solvent systems were used for the first time for solubilization of CGC extracted from the yeast Komagataella pastoris. Different NaOH/urea ratios (6:8, 8:4 and 11:4 (w/w), respectively) were used to obtain aqueous solutions using a freeze/thaw procedure. There was an overall solubilization of 63–68%, with the highest solubilization rate obtained for the highest tested urea concentration (8 wt%). The regenerated polymer, obtained by dialysis of the alkali solutions followed by lyophilization, formed porous macrostructures characterized by a chemical composition similar to that of the starting co-polymer, although the acetylation degree decreased from 61.3% to 33.9–50.6%, indicating that chitin was converted into chitosan, yielding chitosan-glucan complex (ChGC). Consistent with this, there was a reduction of the crystallinity index and thermal degradation temperature. Given these results, this study reports a simple and green procedure to solubilize CGC and obtain aqueous ChGC solutions that can be processed as novel biomaterials.

Indirect bioleaching of Co and Ni from iron rich laterite ore, using metabolic carboxylic acids generated by P. putida, P. koreensis, P. bilaji and A. niger

Indirect bioleaching of Co and Ni from iron rich laterite ore was studied, using spent media produced by four fungal and bacterial species including Pseudomonas putida, Pseudomonas koreensis, Aspergillus niger and Penicillium bilaji. HPLC analysis showed that the main carboxylic acids in spent media were gluconic, citric and oxalic acids. Gluconic acid (with 10.8–14.4 g/l) was the predominant metabolite in spent media of Aspergillus niger and Pseudomonas species, whereas citric acid (with 6.2 g/l) was the main metabolite for Penicillium bilaji. Bioleaching kinetics was assessed at 45, 75 and 90 °C. Results indicated that the highest recovery rate of Ni and Co obtained from spent medium of Pseudomonas putida were 90.6 and 71.98%, achieved at 90 °C after 3 h. The corresponding activation energy for Ni and Co solubilization using spent medium of Pseudomonas putida were 41.82 and 43.91 kJ/mol, indicating that solubilization rate of Ni and Co from iron rich laterite ore is governed by a chemically controlled reaction mechanism.