Tania Castillo

Biotechnological strategies to improve production of microbial poly-(3-hydroxybutyrate): a review of recent research work

Poly‐(3‐hydroxybutyrate) [P(3HB)] is a polyester synthesized as a carbon and energy reserve material by a wide number of bacteria. This polymer is characterized by its thermo‐plastic properties similar to plastics derived from petrochemical industry, such as polyethylene and polypropylene. Furthermore, P(3HB) is an inert, biocompatible and biodegradable material which has been proposed for several uses in medical and biomedical areas. Currently, only few bacterial species such as Cupriavidus necator, Azohydromonas lata and recombinant Escherichia coli have been successfully used for P(3HB) production at industrial level. Nevertheless, in recent years, several fermentation strategies using other microbial models such as Azotobacter vinelandii, A. chroococcum, as well as some methane‐utilizing species, have been developed in order to improve the P(3HB) production and also its mean molecular weight.

Modifying Yeast Tolerance to Inhibitory Conditions of Ethanol Production Processes.

Saccharomyces cerevisiae strains having a broad range of substrate utilization, rapid substrate consumption, and conversion to ethanol, as well as good tolerance to inhibitory conditions are ideal for cost-competitive ethanol production from lignocellulose. A major drawback to directly design S. cerevisiae tolerance to inhibitory conditions of lignocellulosic ethanol production processes is the lack of knowledge about basic aspects of its cellular signaling network in response to stress. Here, we highlight the inhibitory conditions found in ethanol production processes, the targeted cellular functions, the key contributions of integrated -omics analysis to reveal cellular stress responses according to these inhibitors, and current status on design-based engineering of tolerant and efficient S. cerevisiae strains for ethanol production from lignocellulose.

The Effect of Copper on the Color of Shrimps: Redder Is Not Always Healthier

The objective of this research is to test the effects of copper on the color of pacific white shrimp (Litopenaeus vannamei) in vivo. Forty-eight shrimps (L. vannamei) were exposed to a low concentration of copper (1 mg/L; experimental treatment) and forty-eight shrimps were used as controls (no copper added to the water). As a result of this experiment, it was found that shrimps with more copper are significantly redder than those designated as controls (hue (500–700 nm): P = 0.0015; red chroma (625–700 nm): P<0.0001). These results indicate that redder color may result from exposure to copper and challenge the commonly held view that highly pigmented shrimps are healthier than pale shrimps.

Bioprocess Design: Fermentation Strategies for Improving the Production of Alginate and Poly-β-Hydroxyalkanoates (PHAs) by Azotobacter vinelandii

Industrial interest in microbial polymers has been stimulated by their unique properties and the opportunity to develop new materials, which can be used for specific applications in medical and pharmaceutical industries. Azotobacter vinelandii produces two polymers of biotechnological importance; alginate, an extracellular polysaccharide, and poly-┚hydroxybutyrate (PHB), an intracellular polyester of the polyhydroxyalkanoates (PHAs) family (Galindo et al., 2007). Alginates are linear polysaccharides composed of variable amounts of (1–4)-┚-D-mannuronic acid and its epimer, ┙-L-guluronic acid. Alginates present a wide range of applications, acting as stabilizing, thickening, gel or film-forming agents, in various industrial fields. Currently, new applications are being discovered for these polymers, such as their use as a source of soluble fiber, or in medical products. One example is found in the use of alginate gel beads as entrapment devices for transplantation of e. g. insulin producing cells and tissue engineering (Hernandez et al., 2010). The intracellular polyester PHB and other PHAs have been drawing attention because they are biodegradable and biocompatible thermoplastics, which can be processed to create a wide variety of consumer products, including plastics, films, and fibers (Aldor & Keasling, 2003). Recently, and based on their properties of biocompatibility and biodegradability, new attractive applications for PHAs have been proposed in the medical field, where the chemical composition and product purity are critical (Williams & Martin, 2005). The subjects covered in this chapter include research concerning the production of alginate and PHB by A. vinelandii, particularly the molecular regulation of the production of these polymers, the influence of fermentation parameters on the production and composition of alginate and PHB, some reports about the scaling-up of the process and downstream processing, and finally, novel fermentation strategies that could be applied for the production of alginate and PHAs by A. vinelandii.

Molecular mass of Poly-3-hydroxybutyrate (P3HB) produced by Azotobacter vinelandii is influenced by the polymer content in the inoculum

Poly-3-hydroxybutyrate (P3HB) is a biopolymer produced by Azotobacter vinelandii. The physicochemical properties and applications of P3HB are strongly influenced by its weight-average molecular mass (Mw), and in A. vinelandii, it could be influenced by the culture conditions. The aim of this study was to evaluate the effect of the P3HB content of the inoculum on the Mw of the polymer produced by A. vinelandii OP in bioreactor cultures. A. vinelandii cells containing 20, 50 and 70% of P3HB were used as inoculum. The P3HB content in the inoculum affected the volumetric P3HB productivity (qP3HB) and the Mw of P3HB. Those cultures inoculated with cells containing 20% of P3HB, achieved the highest qP3HB (0.17±0.018gP3HBL-1h-1); whereas a P3HB content of 70% was reflected as a low qP3HB (0.021±0.002gP3HBL-1h-1). On the other hand, using an inoculum with 70% of polymer content, the Mw of the biopolymer remained stable at values close to 3200kDa; whereas, when an inoculum with 20% of P3HB was used, the Mw decreased drastically during early stages of cultivation. These results show that manipulating the P3HB content of the inoculum is possible to produce biopolymers with a suitable Mw.

Oxygen uptake rate in alginate producer (algU+) and nonproducer (algU−) strains of Azotobacter vinelandii under nitrogen-fixation conditions

The sigma E (AlgU) in Azotobacter vinelandii has been shown to control the expression of cydR gene, a repressor of genes of the alternative respiratory chain, and alginate has been considered a barrier for oxygen diffusion. Therefore, the aim of the present study was to compare the respiratory activity of an alginate nonproducing strain, lacking the sigma factor E (algU−), and polymer‐producing strains (algU+) of A. vinelandii under diazotrophic conditions at different aeration conditions.

Systems Metabolic Engineering of Saccharomyces cerevisiae for Production of Biochemicals from Biomass

In the production of biofuels and chemicals from biomass-derived sugars, the yeast Saccharomyces cerevisiae has emerged as a key microbial host. Producing these biochemicals in yields and productivities satisfactory to be useful for establishing a cost-effective production process requires the engineering of the yeast’s metabolism. This is a challenging mission since metabolic pathways are intriguingly connected with genetic regulatory circuits, and we are just deciphering these networks. However, global technologies of systems biology in combination with the adequate design capabilities of synthetic biology, and random or rational mutagenesis through adaptive laboratory evolution have emerged to improve our understanding of basic aspects of yeast cellular processes and come up with proper metabolic engineering strategies (the systems metabolic engineering approach). In this chapter, we will review recent advances in systems metabolic engineering of S. cerevisiae for production of biofuels and commodity chemicals from lignocellulosic biomass.