Potential of Acidithiobacillus ferrooxidans to Grow on and Bioleach Metals from Mars and Lunar Regolith Simulants under Simulated Microgravity Conditions

The biomining microbes which extract metals from ores that have been applied in mining processes worldwide hold potential for harnessing space resources. Their cell growth and ability to extract metals from extraterrestrial minerals under microgravity environments, however, remains largely unknown. The present study used the model biomining bacterium Acidithiobacillus ferrooxidans to extract metals from lunar and Martian regolith simulants cultivated in a rotating clinostat with matched controls grown under the influence of terrestrial gravity. Analyses included assessments of final cell count, size, morphology, and soluble metal concentrations. Under Earth gravity, with the addition of Fe3+ and H2/CO2, A. ferrooxidans grew in the presence of regolith simulants to a final cell density comparable to controls without regoliths. The simulated microgravity appeared to enable cells to grow to a higher cell density in the presence of lunar regolith simulants. Clinostat cultures of A. ferrooxidans solubilised higher amounts of Si, Mn and Mg from lunar and Martian regolith simulants than abiotic controls. Electron microscopy observations revealed that microgravity stimulated the biosynthesis of intracellular nanoparticles (most likely magnetite) in anaerobically grown A. ferrooxidans cells. These results suggested that A. ferrooxidans has the potential for metal bioleaching and the production of useful nanoparticles in space.

Characteristics of the growth rate and lipid production in fourteen strains of Baltic green microalgae

Screening of fourteen Baltic green algal strains provided basic data on their mass culture potential for the purpose of valuable biomass production with particular emphasis on lipid content. Selected microalgae were grown under non-stressed conditions in order to identify those characterized by efficient lipid production. The tested strains exhibited significant differences in growth patterns and lipid yields. Strains belonging to Chlorella and Stichococcus genera exhibited the highest growth rates, ranging from 0.39 d-1 to 0.50 d-1 and thus the highest final cell density (> 107 cells ml-1). Furthermore, five strains: C. minutissima BA-12, C. fusca BA-18, C. vulgaris BA-80, Monoraphidium sp. BA-165 and Chlorella sp. BA-167 were characterized by distinctively high lipid yield (> 60 mg l-1). The same strains, together with C. vulgaris BA-02, were also shown as those with the highest volumetric lipid productivity, reaching > 30 mg l-1 d-1. The tested Baltic strains performed well in terms of lipid production compared to the literature data, still leaving a great spectrum of opportunities for further lipid yield improvement.

Effect of Carbon Sources and Fe3+ on the Growth and Lipid Accumulation of Monoraphidium sp. FXY-10 under Mixotrophic Culture Condition

Effects of different carbon source and Fe3+ for the growth and lipid accumulation of Monoraphidium sp. FXY-10 cultured mixotrophically was studied in our present work. The final cell density was reached to 2.626 g L-1 when glucose was the only carbon source, which is 1.43-fold to sodium acetate (1.834 g L-1), far higher than sucrose (0.251 g L-1) and xylitol (0.471 g L-1), but barely grow in other culture condition. Additionally, the highest algae lipid productivity (77.45 mg L-1 d-1) was obtained in 10 g L-1 glucose group, which indicated that glucose was the optimal carbon source for growth and lipid accumulation of Monoraphidium sp. FXY-10. Nevertheless, Monoraphidium sp. FXY-10 was grew slowly in BG-11 culture medium with the absence of Fe3+. The biomass was achieved at the top with 50μM Fe3+ added. With the increase of Fe3+ concentration, it showed no variation in the growth of microalgae. The highest biomass productivity (209.87 mg L-1 d-1) was reached when the Fe3+ concentration was at 150μM while highest lipid productivity (94.05 mg L-1 d-1) reached at 50μM, which indicated that Fe3+ was one of the most indispensable trace elements for the growth and lipid accumulation of Monoraphidium sp. FXY-10.

Expression of Alcaligenes eutrophusFlavohemoprotein and Engineered VitreoscillaHemoglobin-Reductase Fusion Protein for Improved Hypoxic Growth ofEscherichia coli

ABSTRACT Expression of the vhb gene encoding hemoglobin fromVitreoscilla sp. (VHb) in several organisms has been shown to improve microaerobic cell growth and enhance oxygen-dependent product formation. The amino-terminal hemoglobin domain of the flavohemoprotein (FHP) of the gram-negative hydrogen-oxidizing bacterium Alcaligenes eutrophus has 51% sequence homology with VHb. However, like other flavohemoglobins and unlike VHb, FHP possesses a second (carboxy-terminal) domain with NAD(P)H and flavin adenine dinucleotide (FAD) reductase activities. To examine whether the carboxy-terminal redox-active site of flavohemoproteins can be used to improve the positive effects of VHb in microaerobic Escherichia coli cells, we fused sequences encoding NAD(P)H, FAD, or NAD(P)H-FAD reductase activities of A. eutrophus in frame after the vhb gene. Similarly, the gene for FHP was modified, and expression cassettes encoding amino-terminal hemoglobin (FHPg), FHPg-FAD, FHPg-NAD, or FHP activities were constructed. Biochemically active heme proteins were produced from all of these constructions in Escherichia coli, as indicated by their ability to scavenge carbon monoxide. The presence of FHP or of VHb-FAD-NAD reductase increased the final cell density of transformed wild-type E. coli cells approximately 50 and 75%, respectively, for hypoxic fed-batch culture relative to the control synthesizing VHb. Approximately the same final optical densities were achieved with the E. coli strains expressing FHPg and VHb. The presence of VHb-FAD or FHPg-FAD increased the final cell density slightly relative to the VHb-expressing control under the same cultivation conditions. The expression of VHb-NAD or FHPg-NAD fusion proteins reduced the final cell densities approximately 20% relative to the VHb-expressing control. The VHb-FAD-NAD reductase-expressing strain was also able to synthesize 2.3-fold more recombinant β-lactamase relative to the VHb-expressing control.

Reduction of Selenite and Detoxification of Elemental Selenium by the Phototrophic BacteriumRhodospirillum rubrum

ABSTRACT The effect of selenite on growth kinetics, the ability of cultures to reduce selenite, and the mechanism of detoxification of selenium were investigated by using Rhodospirillum rubrum. Anoxic photosynthetic cultures were able to completely reduce as much as 1.5 mM selenite, whereas in aerobic cultures a 0.5 mM selenite concentration was only reduced to about 0.375 mM. The presence of selenite in the culture medium strongly affected cell division. In the presence of a selenite concentration of 1.5 mM cultures reached final cell densities that were only about 15% of the control final cell density. The cell density remained nearly constant during the stationary phase for all of the selenite concentrations tested, showing that the cells were not severely damaged by the presence of selenite or elemental selenium. Particles containing elemental selenium were observed in the cytoplasm, which led to an increase in the buoyant density of the cells. Interestingly, the change in the buoyant density was reversed after selenite reduction was complete; the buoyant density of the cells returned to the buoyant density of the control cells. This demonstrated that R. rubrum expels elemental selenium across the plasma membrane and the cell wall. Accordingly, electron-dense particles were more numerous in the cells during the reduction phase than after the reduction phase.

Adhesion, growth and morphology of human mesothelial cells on extracellular matrix

Human mesothelial cells (HMC) cover a variety of serosal surfaces and have been shown to rest upon an underlying subcellular basement membrane in vivo. Bovine corneal endothelial cells produce an extracellular matrix (ECM) in vitro that mimics HMC subcellular basement membrane and was found to modulate HMC adhesion, morphology and proliferation in vitro. Our results indicated that within minutes after plating, a high percentage (greater than 80%) of HMC firmly attached to ECM. Active cellular migration and subsequent proliferation were observed leading to the formation of a well-organized closely apposed cell monolayer. However, when cells were plated on plastic, the rate of cell attachment was much lower and the proliferative rate of HMC grown on plastic also was strikingly lower (exponential doubling time 4.3 days) than that of cells grown on ECM (exponential doubling time 2.4 days). Cells upon reaching confluency on plastic were markedly enlarged as compared to confluent cells grown on ECM. These observations corroborated differences in final cell density where it was noted that HMC cultured on ECM demonstrated a 10-fold greater final cell density as compared to cells grown on plastic. Results from these studies illustrate the fact that phenotypic expression as well as proliferative responsiveness of HMC can be modulated by adhesive interactions with preformed ECM.

Factors controlling the proliferative rate, final cell density, and life span of bovine vascular smooth muscle cells in culture.

Low density vascular smooth muscle (VSM) cell cultures maintained on extracellular-matrix(ECM)-coated dishes and plated in the presence of either plasma or serum will proliferate actively when serum-containing medium is replaced by a synthetic medium supplemented with three factors: high density lipoprotein (HDL, 250 micrograms protein/ml); insulin (2.5 micrograms/ml) or somatomedin C (10 ng/ml); and fibroblast growth factor (FGF, 100 ng/ml) or epidermal growth factor (EGF, 50 ng/ml). The omission of any of these three factors from the synthetic medium results in a lower growth rate of the cultures, as well as in a lower final cell density once cultures reach confluence. When cells are plated in the total absence of serum, transferrin (10 micrograms/ml) is also required to induce optimal cell growth. The effects of the substrate and medium supplements on the life span of VSM cultures have also been analyzed. Cultures maintained on plastic and exposed to medium supplemented with 5% bovine serum underwent 15 generations. However, when maintained on ECM-coated dishes the serum-fed cultures had a life span of at least 88 generations. Likewise, when cultures were maintained in a synthetic medium supplemented with HDL and either FGF or EGF, an effect on the tissue culture life span by the substrate was observed. Cultures maintained on plastic underwent 24 generations, whereas those maintained on ECM-coated dishes could be passaged repeatedly for 58 generations. These experiments demonstrate the influence of the ECM-substrate only in promoting cell growth but also in increasing the longevity of the cultures.