Oxygen uptake rate in alginate producer (algU+) and nonproducer (algU−) strains ofAzotobacter vinelandiiunder nitrogen-fixation conditions

Castillo, Tania; López, I.; Flores, Celia; Segura, Daniel; García, Adán Guillermo Ramírez; Galindo, Enrique; Peña, Carlos

doi:10.1111/jam.13760

Cited by 15 publications

(4 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Recent studies suggest involvement of EPS in protecting heterotrophic nitrogen fixers of the species Azotobacter vinelandii (12, 51, 52). This has been supported by a laboratory study where respiration decreases with EPS production (53). Trichodesmium produces EPS especially under nutrient-limited conditions (54–56).…”

Section: Discussionmentioning

confidence: 66%

Mechanistic Model for the Coexistence of Nitrogen Fixation and Photosynthesis in Marine Trichodesmium

2019

View full text Add to dashboard Cite

The cyanobacterium Trichodesmium is an important contributor of new nitrogen (N) to the surface ocean, but its strategies for protecting the nitrogenase enzyme from inhibition by oxygen (O2) remain poorly understood. We present a dynamic physiological model to evaluate hypothesized conditions that would allow Trichodesmium to carry out its two conflicting metabolic processes of N2 fixation and photosynthesis. First, the model indicates that managing cellular O2 to permit N2 fixation requires high rates of respiratory O2 consumption. The energetic cost amounts to ∼80% of daily C fixation, comparable to the observed diminution of the growth rate of Trichodesmium relative to other phytoplankton. Second, by forming a trichome of connected cells, Trichodesmium can segregate N2 fixation from photosynthesis. The transfer of stored C to N-fixing cells fuels the respiratory O2 consumption that protects nitrogenase, while the reciprocal transfer of newly fixed N to C-fixing cells supports cellular growth. Third, despite Trichodesmium lacking the structural barrier found in heterocystous species, the model predicts low diffusivity of cell membranes, a function that may be explained by the presence of Gram-negative membrane, production of extracellular polysaccharide substances (EPS), and “buffer cells” that intervene between N2-fixing and photosynthetic cells. Our results suggest that all three factors—respiratory protection, trichome formation, and diffusion barriers—represent essential strategies that, despite their energetic costs, facilitate the growth of Trichodesmium in the oligotrophic aerobic ocean and permit it to be a major source of new reactive nitrogen. IMPORTANCE Trichodesmium is a major nitrogen-fixing cyanobacterium and exerts a significant influence on the oceanic nitrogen cycle. It is also a widely used model organism in laboratory studies. Since the nitrogen-fixing enzyme nitrogenase is extremely sensitive to oxygen, how these surface-dwelling plankton manage the two conflicting processes of nitrogen fixation and photosynthesis has been a long-standing question. In this study, we developed a simple model of metabolic fluxes of Trichodesmium capturing observed daily cycles of photosynthesis, nitrogen fixation, and boundary layer oxygen concentrations. The model suggests that forming a chain of cells for spatially segregating nitrogen fixation and photosynthesis is essential but not sufficient. It also requires a barrier against oxygen diffusion and high rates of oxygen scavenging by respiration. Finally, the model indicates an extremely short life span of oxygen-enabling cells to instantly create a low-oxygen environment upon deactivation of photosynthesis.

show abstract

Section: Discussionmentioning

confidence: 66%

Mechanistic Model for the Coexistence of Nitrogen Fixation and Photosynthesis in Marine Trichodesmium

2019

View full text Add to dashboard Cite

show abstract

“…In addition, in the vegetative stage, alginate may serve as a diffusion barrier for oxygen to protect the nitrification system of the bacteria. 3 Alginate forms ionotropic gels with divalent cations such as calcium where the presence of G-blocks is the main structural feature contributing to gel formation. The mechanism behind gel formation is most easily visualized by analogy with an egg seven epimerase genes (algE1−algE7), all of which have been cloned and expressed in Escerichia coli.…”

Section: ■ Introductionmentioning

confidence: 99%

“…alginate is essential for the cyst formation, where an alginate gel forms the protective walls on metabolic dormant cysts. In addition, in the vegetative stage, alginate may serve as a diffusion barrier for oxygen to protect the nitrification system of the bacteria …”

Section: Introductionmentioning

confidence: 99%

Biosynthesis and Function of Long Guluronic Acid-Blocks in Alginate Produced by Azotobacter vinelandii

et al. 2019

View full text Add to dashboard Cite

With the present accessibility of algal raw material, microbial alginates as a source for strong gelling material are evaluated as an alternative for advanced applications. Recently, we have shown that alginate from algal sources all contain a fraction of very long G-blocks (VLG), that is, consecutive sequences of guluronic acid (G) residues of more than 100 residues. By comparing the gelling properties of these materials with in vitro epimerized polymannuronic acid (poly-M) with shorter G-blocks, but comparable with the G-content, we could demonstrate that VLG have a large influence on gelling properties. Hypothesized to function as reinforcement bars, VLG prevents the contraction of the gels during formation (syneresis) and increases the Young's modulus (strength of the gel). Here we report that these VLG structures are also present in alginates from Azotobacter vinelandii and that these polymers consequently form stable, low syneretic gels with calcium, comparable in mechanical strength to algal alginates with the similar monomeric composition. The bacterium expresses seven different extracellular mannuronan epimerases (AlgE1-AlgE7), of which only the bifunctional epimerase AlgE1 seems to be able to generate the long G-blocks when acting on poly-M. The data implies evidence for a processive mode of action and the necessity of two catalytic sites to obtain the observed epimerization pattern. Furthermore, poly-M epimerized with AlgE1 in vitro form gels with comparable or higher rigidity and gel strength than gels made from brown seaweed alginate with matching G-content. These findings strengthen the viability of commercial alginate production from microbial sources. 51 box. 4 In this model, divalent cations (notably Ca 2+) are 52 coordinated in the cavities between dimers of guluronate from 53 two opposing alginate chains creating junction zones. 54 Eventually this forms a network, provided that there is an 55 average of more than three G-blocks with a minimum length of 56 8 units per polymer chain. 5 This model has been considerably 57 refined through theoretical 6 and experimental 7−9 work. 58 A family of seven secreted mannuronan C-5 epimerases 59 (AlgE1-AlgE7) has been identified in the soil bacterium 60 Azotobacter vinelandii. 10−12 These enzymes catalyze the 61 conversion of D-mannuronic acid into L-guluronic acid by 62

show abstract

“…From the significance of differences at p < 0.05, it can be concluded that bacteria grown in conditions with high aeration and low sucrose concentration in cultural medium do not have sufficient carbon source for constant exponential growth, and, therefore, after 48 h they enter the stationary phase (C−/O+). It can be assumed that the role of carbon as the main source for bacteria growth increases due to high agitation rate (O+) [ 46 ]. So, Barrera and his colleagues demonstrated that upon elevation of the aeration level, A. vinelandii begins to consume carbon as much as possible, where 25% of it is spent on the biosynthesis of alginate [ 47 ].…”

Section: Resultsmentioning

confidence: 99%

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications

et al. 2021

View full text Add to dashboard Cite

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (Mw) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal Mw (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low Mw). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.

show abstract

Oxygen uptake rate in alginate producer (algU+) and nonproducer (algU−) strains ofAzotobacter vinelandiiunder nitrogen-fixation conditions

Abstract: This study highlights the role of AlgU to control respiration of A. vinelandii when exposed to diazotrophy.

Cited by 15 publications

References 39 publications

Mechanistic Model for the Coexistence of Nitrogen Fixation and Photosynthesis in Marine Trichodesmium

Mechanistic Model for the Coexistence of Nitrogen Fixation and Photosynthesis in Marine Trichodesmium

Biosynthesis and Function of Long Guluronic Acid-Blocks in Alginate Produced by Azotobacter vinelandii

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications

Contact Info

Product

Resources

About