High-quality environmentally-friendly bioplastics can be produced by mixing poly-L-lactate with poly-D-lactate. On an industrial scale, this process simultaneously consumes large amounts of both ...optically pure lactate stereoisomers. However, because optimal growth conditions of L-lactate producers often differ from those of D-lactate producers, each stereoisomer is produced in a specialised facility, which raises cost and lowers sustainability. To address this challenge, we metabolically engineered
Lactobacillus gasseri
JCM 1131
T
, a bioprocess-friendly and genetically malleable strain of homofermentative lactic acid bacterium, to efficiently produce either pure L- or pure D-lactate under the same bioprocess conditions. Transformation of
L. gasseri
with plasmids carrying additional genes for L- or D-lactate dehydrogenases failed to affect the ratio of produced stereoisomers, but inactivation of the endogenous genes created strains which yielded 0.96 g of either L- or D-lactate per gram of glucose. In this study, the plasmid pHBintE, routinely used for gene disruption in
Bacillus megaterium
, was used for the first time to inactivate genes in lactobacilli. Strains with inactivated genes for endogenous lactate dehydrogenases efficiently fermented sugars released by enzymatic hydrolysis of alkali pre-treated wheat straw, an abundant lignocellulose-containing raw material, producing 0.37–0.42 g of lactate per gram of solid part of alkali-treated wheat straw. Thus, the constructed strains are primed to serve as producers of both optically pure L-lactate and D-lactate in the next-generation biorefineries.
Graphic abstract
Brewers' spent grains (BSG) are a by-product of the brewing industry that is mainly used as feedstock; otherwise, it has to be disposed according to regulations. Due to the high content of glucose ...and xylose, after pretreatment and hydrolysis, it can be used as a main carbohydrate source for cultivation of microorganisms for production of biofuels or biochemicals like 2,3-butanediol or lactate. 2,3-Butanediol has applications in the pharmaceutical or chemical industry as a precursor for varnishes and paints or in the food industry as an aroma compound. So far,
,
,
, and
are being used and investigated in different bioprocesses aimed at the production of 2,3-butanediol. The main drawback is bacterial pathogenicity which complicates all production steps in laboratory, pilot, and industrial scales. In our study, a gram-positive GRAS bacterium
DSM 742 was used for the production of 2,3-butanediol. Since this strain is very poorly described in literature, bacterium cultivation was performed in media with different glucose and/or xylose concentration ranges. The highest 2,3-butanediol concentration of 18.61 g l
was achieved in medium with 70 g l
of glucose during 40 h of fermentation. In contrast, during bacterium cultivation in xylose containing medium there was no significant 2,3-butanediol production. In the next stage, BSG hydrolysates were used for bacterial cultivation.
DSM 742 cultivated in the liquid phase of pretreated BSG produced very low 2,3-butanediol and ethanol concentrations. Therefore, this BSG hydrolysate has to be detoxified in order to remove bacterial growth inhibitors. After detoxification, bacterium cultivation resulted in 30 g l
of lactate, while production of 2,3-butanediol was negligible. The solid phase of pretreated BSG was also used for bacterium cultivation after its hydrolysis by commercial enzymes. In these cultivations,
DSM 742 produced 9.8 g l
of 2,3-butanediol and 3.93 g l
of ethanol. On the basis of the obtained results, it can be concluded that different experimental setups give the possibility of directing the metabolism of
DSM 742 toward the production of either 2,3-butanediol and ethanol or lactate.
Production of biofuels from renewable feedstocks has captured considerable scientific attention since they could be used to supply energy and alternative fuels. Bioethanol is one of the most ...interesting biofuels due to its positive impact on the environment. Currently, it is mostly produced from sugar- and starch-containing raw materials. However, various available types of lignocellulosic biomass such as agricultural and forestry residues, and herbaceous energy crops could serve as feedstocks for the production of bioethanol, energy, heat and value-added chemicals. Lignocellulose is a complex mixture of carbohydrates that needs an efficient pretreatment to make accessible pathways to enzymes for the production of fermentable sugars, which after hydrolysis are fermented into ethanol. Despite technical and economic difficulties, renewable lignocellulosic raw materials represent low-cost feedstocks that do not compete with the food and feed chain, thereby stimulating the sustainability. Different bioprocess operational modes were developed for bioethanol production from renewable raw materials. Furthermore, alternative bioethanol separation and purification processes have also been intensively developed. This paper deals with recent trends in the bioethanol production as a fuel from different renewable raw materials as well as with its separation and purification processes.
This review aims to present current knowledge of the fungi involved in lignocellulose degradation with an overview of the various classes of lignocellulose‐acting enzymes engaged in the pretreatment ...and saccharification step. Fungi have numerous applications and biotechnological potential for various industries including chemicals, fuel, pulp, and paper. The capability of fungi to degrade lignocellulose containing raw materials is due to their highly effective enzymatic system. Along with the hydrolytic enzymes consisting of cellulases and hemicellulases, responsible for polysaccharide degradation, they have a unique nonenzymatic oxidative system which together with ligninolytic enzymes is responsible for lignin modification and degradation. An overview of the enzymes classification is given by the Carbohydrate‐Active enZymes (CAZy) database as the major database for the identification of the lignocellulolytic enzymes by their amino acid sequence similarity. Finally, the recently discovered novel class of recalcitrant polysaccharide degraders‐lytic polysaccharide monooxygenases (LPMOs) are presented, because of these enzymes importance in the cellulose degradation process.
Značajne količine raznovrsnih ostataka (odnosno lignocelulozne biomase) nastaju u poljoprivredi, prehrambenoj industriji i šumarstvu. Stoga je važno podići svijest o mogućnostima primjene takvih ...materijala koji se u današnje vrijeme ne bi trebali tretirati kao otpad, već se mogu koristiti kao obnovljive biotehnološke sirovine za proizvodnju kemikalija, drugih visokovrijednih proizvoda i biogoriva. Lignocelulozni materijal uglavnom sadrži celulozu, hemicelulozu i lignin. Predmet interesa ovog rada je lignocelulozni otpad iz poljoprivrede i prehrambene industrije kao mogući sirovinski temelj za napredak održive biotehnološke proizvodnje u Republici Hrvatskoj. Razmotrene su dostupne količine ovih lignoceluloznih sirovina, tipovi bioprocesa u kojima se one mogu koristiti, postupci predobrade koje je neophodno provesti prije provedbe samog bioprocesa te vrste biotehnoloških proizvoda koje je moguće dobiti.
Significant amounts of various residues (i.e. lignocellulosic biomass) are generated in agriculture, food industry and forestry. Therefore, it is important to raise awareness about the possibilities of using such materials, which nowadays should not be treated as waste, but can be used as renewable biotechnological raw materials for the production of chemicals, other high-value products and biofuels. Lignocellulosic material consists mainly of cellulose, hemicellulose and lignin. The subject of interest of this paper is lignocellulosic waste from agriculture and the food industry as a possible raw material basis for the progress of sustainable biotechnological production in the Republic of Croatia. The available amounts of these lignocellulosic raw materials, the types of bioprocesses in which they can be used, the pretreatment procedures that need to be carried out before the implementation of the bioprocess itself, and the types of biotechnological products that can be obtained have been considered.
Biodiesel and biogas are two very important sources of renewable energy worldwide, and particularly in the EU countries. While biodiesel is almost exclusively used as transportation fuel, biogas is ...mostly used for production of electricity and heat. The application of more sophisticated purification techniques in production of pure biomethane from biogas allows its delivery to natural gas grid and its subsequent use as transportation fuel. While biogas is produced mostly from waste materials (landfills, manure, sludge from wastewater treatment, agricultural waste), biodiesel in the EU is mostly produced from rapeseed or other oil crops that are used as food, which raises the 'food or fuel' concerns. To mitigate this problem, considerable efforts have been made to use non-food feedstock for biodiesel production. These include all kinds of waste oils and fats, but recently more attention has been devoted to production of microbial oils by cultivation of microorganisms that are able to accumulate high amounts of lipids in their biomass. Promising candidates for microbial lipid production can be found among different strains of filamentous fungi, yeast, bacteria and microalgae. Feedstocks of interest are agricultural waste rich in carbohydrates as well as different lignocellulosic raw materials where some technical issues have to be resolved. In this work, recovery and purification of biodiesel and biogas are also considered.
An innovative integrated bioprocess system for bioethanol production from raw sugar beet cossettes (SBC) and arabitol from remaining exhausted sugar beet cossettes (ESBC) was studied. This integrated ...three-stage bioprocess system is an example of the biorefinery concept to maximise the use of raw SBC for the production of high value-added products such as sugar alcohols and bioethanol.
The first stage of the integrated bioprocess system was simultaneous sugar extraction from SBC and its alcoholic fermentation to produce bioethanol in an integrated bioreactor system (vertical column bioreactor and stirred tank bioreactor) containing a high-density suspension of yeast
(30 g/L). The second stage was the pretreatment of ESBC with dilute sulfuric acid to release fermentable sugars. The resulting liquid hydrolysate of ESBC was used in the third stage as a nutrient medium for arabitol production by non-
yeasts (
CBS 10155 and
CBS 11463).
The obtained results show that the efficiency of bioethanol production increased with increasing temperature and prolonged residence time in the integrated bioreactor system. The maximum bioethanol production efficiency (87.22 %) was observed at a time of 60 min and a temperature of 36 °C. Further increase in residence time (above 60 min) did not result in the significant increase of bioethanol production efficiency. Weak acid hydrolysis was used for ESBC pretreatment and the highest sugar yield was reached at 200 °C and residence time of 1 min. The inhibitors of the weak acid pretreatment were produced below bioprocess inhibition threshold. The use of the obtained liqiud phase of ESBC hydrolysate for the production of arabitol in the stirred tank bioreactor under constant aeration clearly showed that
CBS 10155 with 8.48 g/L of arabitol (
=0.603 g/g and bioprocess productivity of 0.176 g/(L
h)) is a better arabitol producer than
CBS 10155.
An innovative integrated bioprocess system for the production of bioethanol and arabitol was developed based on the biorefinery concept. This three-stage bioprocess system shows great potential for maximum use of SBC as a feedstock for bioethanol and arabitol production and it could be an example of a sustainable 'zero waste' production system.
Various fungal species can degrade lignocellulolytic materials with their enzyme cocktails composed of cellulolytic and lignolytic enzymes. In this work, seven fungal species (
DSM 2185,
CBS 372.70,
...CBS 663.74,
CBS 456.75,
JCM 2738,
f.sp.
JCM 9293, and
JCM 23107) and four nutrient media were used in the screening for effective lignocellulose degrading enzymes. From the seven tested fungi,
and
, along with nutrient medium 4, were selected as the best medium and producers of lignocellulolytic enzymes based on the determined xylanase (>4 U mg
) and glucanase activity (≈2 U mg
). Nutrient medium 4 supplemented with pretreated corn cobs was used in the production of lignocellulolytic enzymes by sequential solid-state and submerged cultivation of
,
, and a mixed culture of both strains.
showed 6 times higher exoglucanase activity (3.33 U mg
) after 5 days of cultivation in comparison with
(0.55 U mg
).
also showed 2 times more endoglucanase activity (0.33 U mg
). The mixed culture cultivation showed similar endo- and exoglucanase activities compared to
(0.35 U mg
; 7.84 U mg
). Maximum xylanase activity was achieved after 7 days of cultivation of
(≈16 U mg
), while
showed maximum activity after 9 days that was around 2 times lower compared to that of
The mixed culture achieved maximum xylanase activity after only 4 days, but the specific activity was similar to activities observed for
It can be concluded that both fungal strains can be used as producers of enzyme cocktails for the degradation of lignocellulose containing raw materials, and that corn cobs can be used as an inducer for enzyme production.
Alternative to the use of fossil fuels are biofuels (e.g., bioethanol, biodiesel and biogas), which are more environmentally friendly and which can be produced from different renewable resources. In ...this investigation, bioethanol production from raw sugar beet cossettes (semi-solid substrate) by yeast Saccharomyces cerevisiae in a horizontal rotating tubular bioreactor (HRTB) was studied. Obtained results show that HRTB rotation mode (constant or interval) and rotation speed have considerable impact on the efficiency of bioethanol production in the HRTB. The main goal of this research was to develop a non-structural mathematical model of bioethanol production from raw sugar beet cossettes in the HRTB. The established mathematical model of bioethanol production in the HRTB describes substrate utilization and product formation (glycerol, ethanol and acetate) and presumes negative impact of high substrate concentration on the working microorganism (substrate inhibition) by using Andrews inhibition kinetics. All simulations of bioethanol production in the HRTB were performed by using Berkeley Madonna software, version 8.3.14 (Berkeley Madonna, Berkeley, CA, USA). The established non-structural bioprocess model describes relatively well the bioethanol production from raw sugar beet cossettes in the HRTB.
Glavni proizvod anaerobne digestije je bioplin, koji je obnovljivo gorivo, a sporedni proizvod ovog procesa je digestat, koji se koristi kao gnojivo bogato hranjivim tvarima. Dodatni pozitivni učinci ...anaerobne digestije su razgradnja organskog otpada te smanjenje neugodnih mirisa i koncentracije patogenih mikroorganizama. Bioplin se uglavnom koristi za proizvodnju električne energije i topline, a u nekim slučajevima se pročišćava da bi se dobio biometan koji se koristi u mreži prirodnog plina, kao gorivo za motore s unutarnjim sagorijevanjem ili kao polazna kemikalija za kemijsku industriju. Zbog svega navedenog, razvoj proizvodnje bioplina ima pozitivne društveno-ekonomske i ekološke učinke. Bioplin proizveden u Hrvatskoj većinom se koristi za proizvodnju električne i toplinske energije u kogeneracijskim postrojenjima. Iako su u Hrvatskoj dostupne različite obnovljive sirovine koje bi se mogle iskoristiti za proizvodnju bioplina, njihov je potencijal do sada bio nedovoljno iskorišten. Kao sirovine za proizvodnju bioplina u nas se pretežno koriste gnojovka i nusproizvodi poljoprivrede, klaonica i prehrambene industrije. Racionalnijim korištenjem zemljišta i razvojem prehrambene industrije mogla bi se povećati količina poljoprivrednih ostataka i nusproizvoda koji nastaju preradom hrane. Usmjeravanjem i poticanjem korištenja ovih nusproizvoda za anaerobnu digestiju može se stimulirati brži razvoj proizvodnje bioplina u Hrvatskoj. Pored mogućeg povećanja vlastite proizvodnje električne energije i goriva, radi se o ekološki povoljnoj tehnologiji koja ima pozitivan društveno-ekonomski učinak.
The main product of anaerobic digestion is biogas, which is a renewable fuel, and the by-product of this process is digestate, which is used as a nutrient-rich fertilizer. Additional positive effects of anaerobic digestion are the decomposition of organic waste and the reduction of unpleasant odors and the concentration of pathogenic microorganisms. Biogas is mainly used for the production of electricity and heat, and in some cases it is purified to obtain biomethane which is used in the natural gas network, as a fuel for internal combustion engines or as a starting chemical for the chemical industry. Due to all of the above, the development of biogas production has positive socio-economic and ecological effects. Biogas produced in Croatia is mostly used for the production of electricity and thermal energy at cogeneration plants. Although various renewable raw materials are available in Croatia that could be used for biogas production, their potential has been underutilized until now. Manure and by-products of agriculture, slaughterhouses and the food industry are mainly used as raw materials for the production of biogas in our country. More rational use of land and development of the food industry could increase the amount of agricultural residues and by-products resulting from food processing. Directing and encouraging the use of these by-products for biogas production can stimulate a faster development of biogas production in our Croatia. In addition to the possible increase in own production of electricity and fuel, it is an environmentally friendly technology that has a positive socio-economic effect.
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