Enhancement of ethanol production from potato-processing wastewater by engineering Escherichia coli using Vitreoscilla haemoglobin

Sphaerotilus natans hemoglobins have an NADH oxidation activity and promote the yield of limonene in an engineered E. coli strain

Bacterial hemoglobins play important roles inside the cell. Phylogenetically, they belong to three different families: the single domain hemoglobin, flavohemoglobin and truncated hemoglobin. Vitreoscilla hemoglobin (VHb) is the first characterized bacterial hemoglobin, and belongs to the single domain hemoglobin family. Heterologous expression of VHb promotes the growth of host cells under microaerobic conditions, and enhances the yield of products during fermentation. Although VHb has been widely applied in the biotechnology field, other bacterial hemoglobins have not demonstrated similar applications. In this study, we identified four bacterial hemoglobins from the microaerobic growing bacterium Sphaerotilus natans, including one flavohemoglobins (FHB) and three truncated hemoglobins (THB1, THB2 and THB3). Absorption spectrum studies validate the existent of the Soret peak and Q-band characteristic to heme and suggest heme groups in FHB and THB1 are hexa- or penta-coordinated, respectively. Our studies demonstrate that FHB and all three truncated hemoglobins have NADH oxidation and radical production activities, which is surprising since truncated hemoglobins do not have a reductase domain that could bind NADH. However, the M. tuberculosis HbN does not show these activities, indicating they are not universal among truncated hemoglobins. Docking studies suggest the nicotinamide ring of NADH may bind to the distal heme pocket of THB1, suggesting the direct electron transfer from NADH to heme might be possible. Our truncated hemoglobins also show peroxidase activities that in THB2 and THB3 could be inhibited by FdR, indicating possible interactions between FdR and truncate hemoglobins. Expression of FHB and THB1 in E. coli could promote cell growth. THB1 also enhances the production of limonene in an engineered E. coli strain, while VHb does not have this effect, which suggests that studies on truncated hemoglobins may lead to the discovery of new and more powerful tools that could have profound impact on biotechnology.

Biotransformation of starch-based wastewater into bioplastics: Optimization of poly(3-hydroxybutyrate) production by Cupriavidus necator DSM 545 using potato wastewater hydrolysate

Biodegradable biopolymers, such as polyhydroxyalkanoates (PHAs), have emerged as an alternative to petrochemical-based plastics. The present work explores the production of PHAs based on the biotransformation of potato processing wastewater and addresses two different strategies for PHA recovery. To this end, culture conditions for PHA synthesis by Cupriavidus necator DSM 545 were optimized on a laboratory scale using a response surface methodology-based experimental design. Optimal conditions rendered a PHB, poly(3-hydroxybutyrate), accumulation of 83.74 ± 2.37 % (5.1 ± 0.2 gL-1), a 1.4-fold increase compared to the initial conditions. Moreover, polymer extraction with non-halogenated agent improved PHB recovery compared to chloroform method (PHB yield up to 78.78 ± 0.57 %), while maintaining PHB purity. (99.83 ± 4.95 %). Overall, the present work demonstrated the potential valorization of starch-based wastewater by biotransformation into PHBs, a high value-added product, and showed that recovery approaches more eco-friendly than the traditional treatments could be applied to PHB recovery to some extent.

The aspects of microbial biomass use in the utilization of selected waste from the agro-food industry

Cellular biomass of microorganisms can be effectively used in the treatment of waste from various branches of the agro-food industry. Urbanization processes and economic development, which have been intensifying in recent decades, lead to the degradation of the natural environment. In the first half of the 20th century, problems related to waste management were not as serious and challenging as they are today. The present situation forces the use of modern technologies and the creation of innovative solutions for environmental protection. Waste of industrial origin are difficult to recycle and require a high financial outlay, while the organic waste of animal and plant origins, such as potato wastewater, whey, lignin, and cellulose, is dominant. In this article, we describe the possibilities of using microorganisms for the utilization of various waste products. A solution to reduce the costs of waste disposal is the use of yeast biomass. Management of waste products using yeast biomass has made it possible to generate new metabolites, such as β-glucans, vitamins, carotenoids, and enzymes, which have a wide range of industrial applications. Exploration and discovery of new areas of applications of yeast, fungal, and bacteria cells can lead to an increase in their effective use in many fields of biotechnology.

Repeated batch fermentation of immobilized E. coli expressing Vitreoscilla hemoglobin for long-term use

This study describes an efficient and reusable process for ethanol production from medium containing whey powder, using alginate immobilized ethanologenic E. coli strains either expressing (TS3) or not expressing (FBR5) Vitreoscilla hemoglobin. Reuseabilities of the FBR5 and TS3 strains were investigated regarding their ethanol production capacities over the course of 15 successive 96-h batch fermentations. The ethanol production was fairly stable over the entire duration of the experiment, with strain TS3 maintaining a substantial advantage over strain FBR5. Storage of both strains in 2 different solutions for up to 60 d resulted in only a modest loss of ethanol production, with strain TS3 consistently outperforming strain FBR5 by a substantial amount. Strains stored for 15 or 30 d maintained their abilities to produce ethanol without dimunition over the course of 8 successive batch fermentations; again strain TS3 maintained a substantial advantage over strain FBR5 throughout the entire experiment. Thus, immobilization is a useful strategy to maintain the advantage in ethanol productivity afforded by expression of Vitreoscilla hemoglobin over long periods of time and large numbers of repeated batch fermentations, including, as in this case, using media with food processing wastes as the carbon source.

Effective ethanol production from whey powder through immobilized E. coli expressing Vitreoscilla hemoglobin

Ethanol production from whey powder was investigated by using free as well as alginate immobilized E. coli and E. coli expressing Vitreoscilla hemoglobin (VHb) in both shake flask and fermenter cultures. Media with varying levels of whey (lactose contents of 3%, 5%, 8% or 15%) and yeast extract (0.3% or 0.5%) were evaluated with fermentation times of 48-96 h. Immobilization and VHb expression resulted in higher ethanol production with all media; the increases ranged from 2% to 89% for immobilization and from 2% to 182% for VHb expression. It was determined that growth medium containing 8% lactose with 0.5% yeast extract yielded the highest ethanol production for free or immobilized strains, with or without VHb expression, in both shake flask and fermenter cultures. Immobilization with alginate was found to be a promising process for ethanol production by VHb-expressing ethanologenic E. coli.

Recent trends in bioethanol production from food processing byproducts

The widespread use of corn starch and sugarcane as sources of sugar for the production of ethanol via fermentation may negatively impact the use of farmland for production of food. Thus, alternative sources of fermentable sugars, particularly from lignocellulosic sources, have been extensively investigated. Another source of fermentable sugars with substantial potential for ethanol production is the waste from the food growing and processing industry. Reviewed here is the use of waste from potato processing, molasses from processing of sugar beets into sugar, whey from cheese production, byproducts of rice and coffee bean processing, and other food processing wastes as sugar sources for fermentation to ethanol. Specific topics discussed include the organisms used for fermentation, strategies, such as co-culturing and cell immobilization, used to improve the fermentation process, and the use of genetic engineering to improve the performance of ethanol producing fermenters.

Efficient ethanol production from potato and corn processing industry waste using E. coli engineered to express Vitreoscilla haemoglobin

Engineering of ethanologenic E. coli to express the haemoglobin (VHb) from the bacterium Vitreoscilla has been shown to enhance ethanol production by fermentation of pure sugars, sugars from hydrolysis of lignocellulose, components of whey, and sugars from wastewater produced during potato processing. Here, these studies were extended to see whether the same effect could be seen when a mixture of waste materials from processing of potatoes and corn into potato and corn chips were used as sugar sources. Consistent increases in ethanol production coincident with VHb expression were seen in shake flasks at both low aeration and high aeration conditions. The ethanol increases were due almost entirely to increases in the amount of ethanol produced per unit of cell mass. The VHb strategy for increasing fermentation to ethanol (and perhaps other valuable fermentation products) may be of general use, particularly regarding conversion of otherwise discarded materials into valuable commodities.

Recent applications of Vitreoscilla hemoglobin technology in bioproduct synthesis and bioremediation

Since its first use in 1990 to enhance production of α-amylase in E. coli, engineering of heterologous hosts to express the hemoglobin from the bacterium Vitreoscilla (VHb) has become a widely used strategy to enhance production of a variety of bioproducts, stimulate bioremediation, and increase growth and survival of engineered organisms. The hosts have included a variety of bacteria, yeast, fungi, higher plants, and even animals. The beneficial effects of VHb expression are presumably the result of one or more of its activities. The available evidence indicates that these include oxygen binding and delivery to the respiratory chain and oxygenases, protection against reactive oxygen species, and control of gene expression. In the past 4 to 5 years, the use of this "VHb technology" has continued in a variety of biotechnological applications in a wide range of organisms. These include enhancement of production of an ever wider array of bioproducts, new applications in bioremediation, a possible role in enhancing aerobic waste water treatment, and the potential to enhance growth and survival of both plants and animals of economic importance.

Improved ethanol production from cheese whey, whey powder, and sugar beet molasses by "Vitreoscilla hemoglobin expressing" Escherichia coli

This work investigated the improvement of ethanol production by engineered ethanologenic Escherichia coli to express the hemoglobin from the bacterium Vitreoscilla (VHb). Ethanologenic E. coli strain FBR5 and FBR5 transformed with the VHb gene in two constructs (strains TS3 and TS4) were grown in cheese whey (CW) medium at small and large scales, at both high and low aeration, or with whey powder (WP) or sugar beet molasses hydrolysate (SBMH) media at large scale and low aeration. Culture pH, cell growth, VHb levels, and ethanol production were evaluated after 48 h. VHb expression in TS3 and TS4 enhanced their ethanol production in CW (21-419%), in WP (17-362%), or in SBMH (48-118%) media. This work extends the findings that "VHb technology" may be useful for improving the production of ethanol from waste and byproducts of various sources.