l
-Amino acids find various applications in biotechnology.
l
-Glutamic acid and its salts are used as flavor enhancers. Other
l
-amino acids are used as food or feed additives, in parenteral ...nutrition or as building blocks for the chemical and pharmaceutical industries.
l
-amino acids are synthesized from precursors of central carbon metabolism. Based on the knowledge of the biochemical pathways microbial fermentation processes of food, feed and pharma amino acids have been developed. Production strains of
Corynebacterium glutamicum
, which has been used safely for more than 50 years in food biotechnology, and
Escherichia coli
are constantly improved using metabolic engineering approaches. Research towards new processes is ongoing. Fermentative production of
l
-amino acids in the million-ton-scale has shaped modern biotechnology and its markets continue to grow steadily. This review focusses on recent achievements in strain development for amino acid production including the use of CRISPRi/dCas9, genome-reduced strains, biosensors and synthetic pathways to enable utilization of alternative carbon sources.
l
-arginine is a semi-essential amino acid with application in cosmetic, pharmaceutical, and food industries. Metabolic engineering strategies have been applied for overproduction of
l
-arginine by
...Corynebacterium glutamicum
. LysE was the only known
l
-arginine exporter of this bacterium. However, an
l
-arginine-producing strain carrying a deletion of
lysE
still accumulated about 10 mM
l
-arginine in the growth medium. Overexpression of the putative putrescine and cadaverine export permease gene
cgmA
was shown to compensate for the lack of
lysE
with regard to
l
-arginine export. Moreover, plasmid-borne overexpression of
cgmA
rescued the toxic effect caused by feeding of the dipeptide Arg-Ala to
lysE
-deficient
C. glutamicum
and
argO
-deficient
Escherichia coli
strains. Deletion of the repressor gene
cgmR
improved
l
-arginine titers by 5 %. Production of
l
-lysine and
l
-citrulline was not affected by
cgmA
overexpression. Taken together, CgmA may function as an export system not only for the diamine putrescine and cadaverine but also for
l
-arginine. The major export system for
l
-lysine and
l
-arginine LysE may also play a role in
l
-citrulline export since production of
l
-citrulline was reduced when
lysE
was deleted and improved by 45 % when
lysE
was overproduced.
Gamma-aminobutyric acid (GABA), a non-protein amino acid widespread in nature, is a component of pharmaceuticals, foods, and the biodegradable plastic polyamide 4.
Corynebacterium glutamicum
shows ...great potential for the production of GABA from glucose. GABA added to the growth medium hardly affected growth of
C. glutamicum,
since a half-inhibitory concentration of 1.1 M GABA was determined. As alternative to GABA production by glutamate decarboxylation, a new route for the production of GABA via putrescine was established in
C. glutamicum
. A putrescine-producing recombinant
C. glutamicum
strain was converted into a GABA producing strain by heterologous expression of putrescine transaminase (PatA) and gamma-aminobutyraldehyde dehydrogenase (PatD) genes from
Escherichia coli
. The resultant strain produced 5.3 ± 0.1 g L
−1
of GABA. GABA production was improved further by adjusting the concentration of nitrogen in the culture medium, by avoiding the formation of the by-product N-acetylputrescine and by deletion of the genes for GABA catabolism and GABA re-uptake. GABA accumulation by this strain was increased by 51 % to 8.0 ± 0.3 g L
−1
, and the volumetric productivity was increased to 0.31 g L
−1
h
−1
; the highest volumetric productivity reported so far for fermentative production of GABA from glucose in shake flasks was achieved.
•Successful immobilization of a laccase on bacterial cellulose for wound dressings.•Bacterial cellulose structure is manly formed by pure crystalline Iα cellulose.•Activation energies and optimum pH ...of free laccase depend on the substrate employed.•Entrapped laccase maintains some flexibility and accessibility of the substrate.•Antimicrobial effect of immobilized laccase in Gram-positive and negative bacteria
This work studied the physical immobilization of a commercial laccase on bacterial nanocellulose (BNC) aiming to identify the laccase antibacterial properties suitable for wound dressings. Physico-chemical analysis demonstrates that the BNC structure is manly formed by pure crystalline Iα cellulose. The pH optimum and activation energy of free laccase depends on the substrate employed corresponding to pH 6, 7, 3 and 57, 22, 48kJmol−1 for 2,6-dimethylphenol (DMP), catechol and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), respectively. The Michaelis–Menten constant (Km) value for the immobilized laccase (0.77mM) was found to be almost double of that of the free enzyme (0.42mM). However, the specific activities of immobilized and free laccase are similar suggesting that the cage-like structure of BNC allows entrapped laccase to maintain some flexibility and favour substrate accessibility. The results clearly show the antimicrobial effect of laccase in Gram-positive (92%) and Gram-negative (26%) bacteria and cytotoxicity acceptable for wound dressing applications.
When direct flow velocity measurements are not feasible, the use of tracers can be a valuable tool. In the present study, both laboratory and field experiments were conducted to evaluate the ...applicability of quinine as a fluorescent tracer for estimating mean sheet flow velocities in different ambient light and surface morphology conditions. Quinine excels in low-light conditions when exposed to UVA light. This tracer was compared with dye and thermal tracers, all in liquid form. In these tracing techniques the tracers were injected into the flow, after which surface velocity was estimated by tracking the leading edge of the tracer plumes and applying a correction factor to calculate the mean velocity (in a water column). The visibility of the tracers was evaluated by measuring the relative luminance and contrast ratio of the quinine and dye tracer plumes. Results show that the quinine tracer can be used to estimate sheet flow velocities over a wide variety of soil and urban surfaces; it has better visibility in comparison to the dye tracer but, in some conditions, lower visibility than the thermal tracer. Although quinine is invisible under bright ambient light conditions, this tracer technique requires low-cost experimental setup and is useful in low-light conditions (e.g., night; twilight; shielded environments).
AbstractCatchment geomorphology is one of the most important factors governing runoff and erosion. However, its complexity is difficult to describe accurately; thus, for simplicity, many studies ...assume hillslopes with a uniform sloping profile. The influence of this simplification on estimating the rainfall-runoff and sediment loss processes is not well understood. In an effort to improve our understanding, this study relies on laboratory experiments using a movable rainfall simulator and a 6-m-long, 3-segment soil flume to simulate the effect of static and moving storms on differently shaped hillslopes: uniform, convex, concave, convex-concave, and concave-convex profiles. Therefore, variables, such as rainfall intensity, soil and water characteristics, and storm speed, were kept constant throughout the experiments. The work confirms empirically that storm movement and hillslope shape are central factors in the soil loss and overland flow processes. The results led to the following conclusions: (1) hillslope shape affected erosion for both nonmoving and moving rainstorms; (2) downslope moving storms led to higher runoff and sediment loss peaks than upslope moving storms; and (3) convex surfaces were the most hazardous in terms of the generation of runoff and erosion.
This study presents a tracer technique based on the fluorescent properties of quinine to help on the visualization of shallow flows and allow a quantitative measurement of overland flow velocities. ...Laboratory experiments were conducted to compare the traditional dye tracer and thermal tracer techniques with this novel fluorescent (quinine) tracer by injecting a quinine solution and the other tracers into shallow flowing surface water. The leading-edge tracer velocities, estimated using videos of the experiments with the quinine tracer were compared with the velocities obtained by using thermograms and real imaging videos of the dye tracers. The results show that the quinine tracer can be used to estimate both overland and rill flow velocities, since measurements are similar to those resulting from using other commonly used tracers. The main advantage of using the quinine tracer is the higher visibility of the injected tracer under ultraviolet A (UVA) light for low luminosity conditions. In addition, smaller amounts of quinine tracer are needed than for dye tracers, which lead to smaller disturbances in the flow. It requires a simple experimental setup and is non-toxic to the environment.
Caesarean section is one of the most common surgeries worldwide, even though there is no evidence supporting maternal and perinatal long-term benefits. Furthermore, the mechanical behavior of a ...caesarean scar during a vaginal birth after caesarean (VBAC) is not well understood since there are several questions regarding the uterine wound healing process. The aim of this study is to investigate the biomechanical Maylard fiber reorientation and stiffness influence during a VBAC through computational methods. A biomechanical model comprising a fetus and a uterus was developed, and a chemical–mechanical constitutive model that triggers uterine contractions was used, where some of the parameters were adjusted to account for the matrix and fiber stiffness increase in the caesarean scar. Several mechanical simulations were performed to analyze different scar fibers arrangements, considering different values for the respective matrix and fibers stiffness. The results revealed that a random fiber arrangement in the Maylard scar has a much higher impact on its mechanical behavior during a VBAC than the common fibers arrangement present in the uninjured uterine tissue. An increase of the matrix scar stiffness exhibits a lower impact, while an increase of the fiber’s stiffness has no significant influence.
The jaguar is the top predator of the Atlantic Forest (AF), which is a highly threatened biodiversity hotspot that occurs in Brazil, Paraguay and Argentina. By combining data sets from 14 research ...groups across the region, we determine the population status of the jaguar and propose a spatial prioritization for conservation actions. About 85% of the jaguar's habitat in the AF has been lost and only 7% remains in good condition. Jaguars persist in around 2.8% of the region, and live in very low densities in most of the areas. The population of jaguars in the AF is probably lower than 300 individuals scattered in small sub-populations. We identified seven Jaguar Conservation Units (JCUs) and seven potential JCUs, and only three of these areas may have ≥50 individuals. A connectivity analysis shows that most of the JCUs are isolated. Habitat loss and fragmentation were the major causes for jaguar decline, but human induced mortality is the main threat for the remaining population. We classified areas according to their contribution to jaguar conservation and we recommend management actions for each of them. The methodology in this study could be used for conservation planning of other carnivore species.
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