Yeast extracts from different manufacturers and supplementation of amino acids and micro elements reveal a remarkable impact on alginate production by A. vinelandii ATCC9046

BACKGROUND

In research and production, reproducibility is a key factor, to meet high quality and safety standards and maintain productivity. For microbial fermentations, complex substrates and media components are often used. The complex media components can vary in composition, depending on the lot and manufacturing process. These variations can have an immense impact on the results of biological cultivations. The aim of this work was to investigate and characterize the influence of the complex media component yeast extract on cultivations of Azotobacter vinelandii under microaerobic conditions. Under these conditions, the organism produces the biopolymer alginate. The focus of the investigation was on the respiration activity, cell growth and alginate production.

RESULTS

Yeast extracts from 6 different manufacturers and 2 different lots from one manufacturer were evaluated. Significant differences on respiratory activity, growth and production were observed. Concentration variations of three different yeast extracts showed that the performance of poorly performing yeast extracts can be improved by simply increasing their concentration. On the other hand, the results with well-performing yeast extracts seem to reach a saturation, when their concentration is increased. Cultivations with poorly performing yeast extract were supplemented with grouped amino acids, single amino acids and micro elements. Beneficial results were obtained with the supplementation of copper sulphate, cysteine or a combination of both. Furthermore, a correlation between the accumulated oxygen transfer and the final viscosity (as a key performance indicator), was established.

CONCLUSION

The choice of yeast extract is crucial for A. vinelandii cultivations, to maintain reproducibility and comparability between cultivations. The proper use of specific yeast extracts allows the cultivation results to be specifically optimised. In addition, supplements can be applied to modify and improve the properties of the alginate. The results only scratch the surface of the underlying mechanisms, as they are not providing explanations on a molecular level. However, the findings show the potential of optimising media containing yeast extract for alginate production with A. vinelandii, as well as the potential of targeted supplementation of the media.

Growth, respiratory activity and chlorpyrifos biodegradation in cultures of Azotobacter vinelandii ATCC 12837

This study aimed to evaluate the growth, respiratory activity, and biodegradation of chlorpyrifos in cultures of Azotobacter vinelandii ATCC 12837. A strategy based on the modification of culture media and aeration conditions was carried out to increase the cell concentration of A. vinelandii, in order to favor and determine its tolerance to chlorpyrifos and its degradation ability. The culture in shaken flasks, using sucrose as a carbon source, significantly improved the growth compared to media with mannitol. When the strain was cultivated under oxygen-limited (5.5, 11.25 mmol L⁻¹ h⁻¹) and no-oxygen-limited conditions (22 mmol L⁻¹ h⁻¹), the growth parameters were not affected. In cultures in a liquid medium with chlorpyrifos, the bacteria tolerated a high pesticide concentration (500 ppm) and the growth parameters were improved even under conditions with a reduced carbon source (sucrose 2 g L⁻¹). The strain degraded 99.6% of chlorpyrifos at 60 h of cultivation, in co-metabolism with sucrose; notably, A. vinelandii ATCC 12837 reduced by 50% the initial pesticide concentration in only 6 h (DT₅₀).

Production of Poly-3-Hydroxybutyrate (P3HB) with Ultra-High Molecular Weight (UHMW) by Mutant Strains of Azotobacter vinelandii Under Microaerophilic Conditions

Poly-3-hydroxybutyrate (P3HB) is a biopolymer, which presents characteristics similar to those of plastics derived from the petrochemical industry. The thermomechanical properties and biodegradability of P3HB are influenced by its molecular weight (MW). The aim of the present study was to evaluate the changes of the molecular weight of P3HB as a function of oxygen transfer rate (OTR) in the cultures using two strains of Azotobacter vinelandii, a wild-type strain OP, and PhbZ1 mutant with a P3HB depolymerase inactivated. Both strains were grown in a bioreactor under different OTR conditions. An inverse relationship was found between the average molecular weight of P3HB and the OTR_max, obtaining a polymer with a maximal MW (8000-10,000 kDa) from the cultures developed at OTR_max of 5 mmol L^-1 h^-1 using both strains, with respect to the cultures conducted at 8 and 11 mmol L^-1 h^-1, which produced a P3HB between 4000 and 5000 kDa. The increase in MW of P3HB was related to the activity of enzymes involved in the synthesis and depolymerization. Overall, our results show that it is possible to modulate the average molecular weight of P3HB by manipulating oxygen transfer conditions with both strains (OP and PhbZ1 mutant) of A. vinelandii.

A novel intracellular nitrogen-fixing symbiosis made by Ustilago maydis and Bacillus spp

We observed that the maize pathogenic fungus Ustilago maydis grew in nitrogen (N)-free media at a rate similar to that observed in media containing ammonium nitrate, suggesting that it was able to fix atmospheric N2 . Because only prokaryotic organisms have the capacity to reduce N2 , we entertained the possibility that U. maydis was associated with an intracellular bacterium. The presence of nitrogenase in the fungus was analyzed by acetylene reduction, and capacity to fix N2 by use of (15) N2 . Presence of an intracellular N2 -fixing bacterium was analyzed by PCR amplification of bacterial 16S rRNA and nifH genes, and by microscopic observations. Nitrogenase activity and (15) N incorporation into the cells proved that U. maydis fixed N2 . Light and electron microscopy, and fluorescence in situ hybridization (FISH) experiments revealed the presence of intracellular bacteria related to Bacillus pumilus, as evidenced by sequencing of the PCR-amplified fragments. These observations reveal for the first time the existence of an endosymbiotic N2 -fixing association involving a fungus and a bacterium.

Structural and thermodynamic folding characterization of triosephosphate isomerases from Trichomonas vaginalis reveals the role of destabilizing mutations following gene duplication

We report the structures and thermodynamic analysis of the unfolding of two triosephosphate isomerases (TvTIM1 and TvTIM2) from Trichomonas vaginalis. Both isoforms differ by the character of four amino acids: E/Q 18, I/V 24, I/V 45, and P/A 239. Despite the high sequence and structural similarities between both isoforms, they display substantial differences in their stabilities. TvTIM1 (E18, I24, I45, and P239) is more stable and less dissociable than TvTIM2 (Q18, V24, V45, and A239). We postulate that the identities of residues 24 and 45 are responsible for the differences in monomer stability and dimer dissociability, respectively. The structural difference between both amino acids is one methyl group. In TvTIMs, residue 24 is involved in packing α-helix 1 against α-helix 2 of each monomer and residue 45 is located at the center of the dimer interface forming a "ball and socket" interplay with a hydrophobic cavity. The mutation of valine at position 45 for an alanine in TvTIM2 produces a protein that migrates as a monomer by gel filtration. A comparison with known TIM structures indicates that this kind of interplay is a conserved feature that stabilizes dimeric TIM structures. In addition, TvTIMs are located in the cytoplasm and in the membrane. As TvTIM2 is an easily dissociable dimer, the dual localization of TvTIMs may be related to the acquisition of a moonlighting activity of monomeric TvTIM2. To our knowledge, this is the simplest example of how a single amino acid substitution can provide alternative function to a TIM barrel protein.