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Continuous Succinic Acid Fermentation by Actinobacillus Succinogenes: Assessment of Growth and Succinic Acid Production Kinetics
No full textSuccinic acid is one of the most interesting platform chemicals that can be produced in a biorefinery approach. The paper reports the characterization of the growth kinetics of Actinobacillus succinogenes DSM 22257 using glucose as carbon source. Tests were carried out in a continuous bioreactor operated under controlled pH. Under steady-state conditions, the conversion process was characterized in terms of concentration of glucose, cells, acids, and pH. The effects of acid—succinic, acetic, and formic—concentration in the medium on fermentation performance were investigated. The fermentation was interpreted according to several models characterized by substrate and product inhibition. The selected kinetic model of biomass growth and of metabolite production described the microorganism growth rate under a broad interval of operating conditions. Under the investigated operating conditions, results pointed out that: no substrate inhibition was observed; acetic acid did not inhibit the cell growth and succinic acid productio
Succinic acid production from hexoses and pentoses by fermentation of actinobacillus succinogenes
No full textSuccinic acid is a precursor for many chemicals in the food, pharmaceutical, cosmetic, and biodegradable plastics industries. Nowadays, the biotechnological route to produce succinic acid is focused on processes based on the fermentation of natural materials characterized by high fraction of carbohydrates. Actinobacillus succinogenes is proposed in the literature as a promising strain for the production of succinic acid. Indeed, A. succinogenes may utilize a wide spectrum of carbohydrates as carbon sources. Moreover, the CO2 required for the fermentation allows to include the biotechnological route among the carbon capture and conversion processes. A key issue of fermentation processes aimed at producing succinic acid is the feedstock cost. Pre-requisites of the feedstock are: availability at high mass flow rate over all the year, and non-competitive with (human and animal) food. Lignocellulosic biomass is a potential feedstock because it fulfils the listed pre-requisites. This contribution reports the characterization of succinic acid fermentation by A. succinogenes 130Z adopting as carbon source sugars representative of the hydrolysis of lignocellulosic biomass: glucose, mannose, arabinose, and xylose. Batch fermentation tests were carried out using single sugar as carbon source for a systematic characterization of the conversion process of the investigated sugars. The conversion process was characterized in terms of concentration of biomass, sugars, and acids as well as of pH. The time-resolved data were processed to assess the sugar conversion, the succinic acid yield, and the productivity for each of the investigated sugars. A. succinogenes was able to convert all investigated sugars into succinic acid using MgCO3 as an indirect CO2 source. Glucose was the sugar characterized by the best performance when the initial concentration was set at 40 g/L. The performances did not depend on the investigated sugars if the initial concentration was quite low (<5 g/L)
Biosuccinic Acid from Lignocellulosic-Based Hexoses and Pentoses by Actinobacillus succinogenes: Characterization of the Conversion Process
No full textSuccinic acid (SA) is a well-established chemical building block. Actinobacillus succinogenes fermentation is by far the most investigated route due to very promising high SA yield and titer on several sugars. This study contributes to include the SA production within the concept of biorefinery of lignocellulose biomass. The study was focused on the SA production by A. succinogenes DSM 22257 using sugars representative from lignocellulose hydrolysis— glucose, mannose, arabinose, and xylose—as carbon source. Single sugar batch fermentation tests and mixture sugar fermentation tests were carried out. All the sugars investigated were converted in succinic acid by A. succinogenes. The best fermentation performances were measured in tests with glucose as carbon source. The bacterial growth kinetics was characterized by glucose inhibition. No inhibition phenomena were observed with the other sugar investigated. The sugar mixture fermentation tests highlighted the synergic effects of the copresence of the four sugars. Under the operating conditions tested, the final concentration of succinic acid in the sugar mixture test was larger (27 g/L) than that expected (25.5 g/L) by combining the fermentation of the single sugar. Moreover, the concentration of acetic and formic acid was lower, consequently obtaining an increment in the succinic acid specificity
Microbial detection and identification methods: Bench top assays to omics approaches
No full textRapid detection of foodborne pathogens, spoilage microbes, and other biological contaminants in complex food matrices is essential to maintain food quality and ensure consumer safety. Traditional methods involve culturing microbes using a range of nonselective and selective enrichment methods, followed by biochemical confirmation among others. The time-to-detection is a key limitation when testing foods, particularly those with short shelf lives, such as fresh meat, fish, dairy products, and vegetables. Some recent detection methods developed include the use of spectroscopic techniques, such as matrix-assisted laser desorption ionization-time of flight along with hyperspectral imaging protocols.This review presents a comprehensive overview comparing insights into the principles, characteristics, and applications of newer and emerging techniques methods applied to the detection and identification of microbes in food matrices, to more traditional benchtop approaches. The content has been developed to provide specialist scientists a broad view of bacterial identification methods available in terms of their benefits and limitations, which may be useful in the development of future experimental design. The case is also made for incorporating some of these emerging methods into the mainstream, for example, underutilized potential of spectroscopic techniques and hyperspectral imaging
BIOFILM REACTORS FOR INTENSIVE PRODUCTION OF BICARBOXYLIC ACIDS
Get PDFThe study carried out during the present Ph.D. program aimed at investigating succinic acid production by fermentation. The work was carried out at the Dipartimento di Ingegneria Chimica, dei Materiale e della Produzione Industriale of the Università degli Studi di Napoli ‘Federico II’. The commercial strain Actinobacillus succinogenes DSM 792 was selected for its ability to produce succinic acid at high concentration and yield from a broad variety of carbon source. The activities were articulated along the two paths described hereinafter.
Characterization of the succinic acid fermentation process as regards the concentration and yields
The study was aimed at the assessment of the fermentation performance - in terms of succinic acid concentration and yield – with reference to two classes of feedstocks: 1) sugars typically present in lignocellulosic hydrolysates (glucose, mannose, arabinose and xylose); 2) high sugar content beverages (HSCBs).
The investigations were carried out with batch fermentation of free A. succinogenes cells at different sugar concentration. The conversion process was characterized in terms of metabolite production (succinic acid, formic acid and acetic acid), sugar conversion, pH and cell concentration. The study included tests with single sugar and sugar mixtures (synthetic and commercial): i) glucose, mannose, arabinose and xylose (GMAX) to mime the composition of a lignocellulosic hydrolysate; ii) sucrose, glucose and fructose (SGF), the sugars typically present in leftover beverages.
All the investigated sugars were converted in succinic acid by A. succinogenes. Tests with mixtures pointed out that the fermentation took advantage of the co-presence of different sugars with respect to the tests carried out with single sugars. The synergy effect of the sugars led to an increase in final succinic acid concentration and SA selectivity.
Development of a continuous process for the succinic acid production
Continuous fermentation tests carried out in a CSTR were aimed to the systematic characterization of the kinetics of cell growth and succinic acid production. The continuous fermentation were carried out by feeding the CSTR with a glucose bearing medium at a wide interval of dilution rate.
The kinetics of A. succinogenes growth on glucose was investigated by assessing the effects of glucose and acids - succinic, acetic, and formic - on cell growth. The experimental results were successfully correlated by a multiple product-inhibited interacted growth model. Experimental results pointed out the individual inhibitory effect of the acids on A. succinogenes growth. Under the investigated operating conditions, results pointed out that: no substrate inhibition was observed; acetic acid did not inhibit the cell growth and the succinic acid production.
The activity aimed at the intensive succinic acid production regarded the design, set-up, operation and optimisation of a packed bed biofilm reactor (PBBR). The effects of the operating conditions - dilution rate (D) and medium compositions (glucose, GX, xylose, GAX) - on the PBBR performances were investigated. Succinic acid concentration, productivity and sugar(s) conversion generally decreased with D. A maximum succinic acid productivity of 35.0 g/L*h was achieved at a D= 1.9 h-1. The effect of HMF and furfural, the main inhibitors found in lignocellulosic hydrolysate, on succinic acid production was also investigated. HMF resulted to have a higher inhibition effect on succinic acid production compared to furfural
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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