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Serotonin, as a monoamine neurotransmitter, modulates the activity of the nervous system. Due to its importance in the coordination of movement and regulation of mood, impairments in the synthesis and homeostasis of serotonin are involved in numerous disorders, including depression, Parkinson's disease, and anxiety. Currently, serotonin is primarily obtained via natural extraction. But this method is time-consuming and low yield, as well as unstable supply of raw materials. With the development of synthetic biology, researchers have established the method of microbial synthesis of serotonin. Compared with natural extraction, microbial synthesis has the advantages of short production cycle, continuous production, not limited by season and source, and environment-friendly; hence, it has garnered considerable research attention. However, the yield of serotonin is still too low to industrialization. Therefore, this review provides the latest progress and examples that illustrate the synthesis pathways of serotonin as well as proposes strategies for increasing the production of serotonin. Key points: • Two biosynthesis pathways of serotonin are introduced. • L-tryptophan hydroxylation is the rate-limiting step in serotonin biosynthesis. • Effective strategies are proposed to improve serotonin production. [ABSTRACT FROM AUTHOR]

In recent years, the risk from environmental pollution caused by chloramphenicol (CAP) has emerged as a serious concern worldwide, especially for the co-selection of antibiotic resistance microorganisms simultaneously exposed to CAP and salts. In this study, the multistage contact oxidation reactor (MCOR) was employed for the first time to treat the CAP wastewater under the co-existence of CAP (10–80 mg/L) and salinity (0–30 g/L NaCl). The CAP removal efficiency reached 91.7% under the co-existence of 30 mg/L CAP and 10 g/L NaCl in the influent, but it fluctuated around 60% with the increase of CAP concentration and salinity. Trichococcus and Lactococcus were the major contributors to the CAP and salinity shock loads. Furthermore, the elevated CAP and salinity selection pressures inhibited the spread of CAP efflux pump genes, including cmlA, tetC, and floR, and significantly affected the composition and abundance of antibiotic resistance genes (ARGs). As the potential hosts of CAP resistance genes, Acinetobacter, Enterococcus, and unclassified_d_Bacteria developed resistance against high osmotic pressure and antibiotic environment using the efflux pump mechanism. The results also revealed that shifting of potential host bacteria significantly contributed to the change in ARGs. Overall, the co-existence of CAP and salinity promoted the enrichment of core genera Trichococcus and Lactococcus; however, they inhibited the proliferation of ARGs. Key points: • Trichococcus and Lactococcus were the core bacteria related to CAP biodegradation • Co-existence of CAP and salinity inhibited proliferation of cmlA, tetC, and floR • The microorganism resisted the CAP using the efflux pump mechanism [ABSTRACT FROM AUTHOR]

Pseudomonas putida NCIMB 9866 utilizes p-cresol or 2,4-xylenol as a sole carbon and energy source. Enzymes catalyzing the oxidation of the para-methyl group of p-cresol have been studied in detail. However, those responsible for the oxidation of the para-methyl group in 2,4-xylenol catabolism are still not reported. In this study, real-time quantitative PCR analysis indicated pchC- and pchF-encoded p-cresol methylhydroxylase (PCMH) and pchA-encoded p-hydroxybenzaldehyde dehydrogenase (PHBDD) in p-cresol catabolism were also likely involved in the catabolism of 2,4-xylenol. Enzyme activity assays and intermediate identification indicated that the PCMH and PHBDD catalyzed the oxidations of 2,4-xylenol to 4-hydroxy-3-methylbenzaldehyde and 4-hydroxy-3-methylbenzaldehyde to 4-hydroxy-3-methylbenzoic acid, respectively. Furthermore, the PCMH-encoding gene pchF was found to be necessary for the catabolism of 2,4-xylenol, whereas the PHBDD-encoding gene pchA was not essential for the catabolism by gene knockout and complementation. Analyses of the maximum specific growth rate ( μ) and specific activity of the gene-knockout strain to different intermediates revealed the presence of other enzyme(s) with PHBDD activity in strain 9866. However, PHBDD played a major role in the catabolism of 2,4-xylenol in contrast to the other enzyme(s). [ABSTRACT FROM AUTHOR]

Rabies virus (RABV) causes a fatal infectious disease, but effective protection may be achieved with the use of rabies immunoglobulin and a rabies vaccine. Virus-neutralizing antibodies (VNA), which play an important role in the prevention of rabies, are commonly evaluated by the RABV neutralizing test. For determining serum VNA levels or virus titers during the RABV vaccine manufacturing process, reliability of the assay method is highly important and mainly dependent on the diagnostic antibody. Most diagnostic antibodies are monoclonal antibodies (mAbs) made from hybridoma cell lines and are costly and time consuming to prepare. Thus, production of a cost-effective mAb for determining rabies VNA levels or RABV titers is needed. In this report, we describe the prokaryotic production of a RABV-specific single-chain variable fragment (scFv) protein with a His-tag (scFv98H) from a previously constructed plasmid in a bioreactor, including the purification and refolding process as well as the functional testing of the protein. The antigen-specific binding characteristics, affinity, and relative affinity of the purified protein were tested. The scFv98H antibody was compared with a commercial RABV nucleoprotein mAb for assaying the VNA level of anti-rabies serum samples from different sources or testing the growth kinetics of RABV strains for vaccine manufactured in China. The results indicated that scFv98H may be used as a novel diagnostic tool to assay VNA levels or virus titers and may be used as an alternative for the diagnostic antibody presently employed for these purposes. [ABSTRACT FROM AUTHOR]

Enteric bacterial pathogens in sewage sludge easily become viable but nonculturable (VBNC) during anaerobic digestion, which escape detection by standard culture methods and pose a potential health risk. In this study, a method that is combining the standard culture method with the reverse transcription quantitative PCR (RT-qPCR) assay was developed for the quantification of bacterial pathogens in the VBNC state. The cycle threshold ( C) values from RT-qPCR assays were linear to the bacterial number in the range from 10 to 10 most probable number (MPN) per reaction for Escherichia coli ( R = 0.9964) and Salmonella typhimurium ( R = 0.9938) and from 10 to 10 MPN per reaction for Shigella flexneri ( R = 0.997), respectively. Mesophilic anaerobic digestion (MAD) caused the bacterial pathogens in sewage sludge entering into VBNC state with the incidence indexes of 0.01-1.12 for E. coli, 2.48-436.52 for S. typhimurium, and 4.17-6.61 for S. flexneri, respectively. Given different VBNC incidence indexes of bacterial pathogens in sewage sludge by MAD, the quantification results of VBNC pathogens using RT-qPCR could provide an improved evaluation of pathogen inactivation efficiency and biological safety in sludge anaerobic digestion. [ABSTRACT FROM AUTHOR]

The self-assembly of biomacromolecules is an extremely important process. It is potentially useful in the fields of life science and materials science. To carry out the study on the self-assembly of proteins, it is necessary to find out the suitable self-assembly conditions, which have always been a challenging task in practice. Inspired by the screening technique in the field of protein crystallization, we proposed using the same screening technique for seeking suitable protein self-assembly conditions. Based on this consideration, we selected 5 proteins (β-lactoglobulin, hemoglobin, pepsin, lysozyme, α-chymotrypsinogen (II) A) together with 5 screening kits (IndexTM, BML, Morpheus, JCSG, PEG/Ion ScreenTM) to investigate the performance of these crystallization screening techniques in order to discover new optimized conditions of protein self-assembly. The screens were all kept at 293 K for certain days, and were analyzed using optical microscope, scanning electron microscope, transmission electron microscope, atomic force microscope, fluorescence microscope, and atomic absorption spectroscope. The results demonstrated that the method of protein crystallization screening can be successfully applied in the screening of self-assembly conditions. This method is fast, high throughput, and easily implemented in an automated system, with a low protein consumption feature. These results suggested that such strategy can be applied to finding new conditions or forms in routine research of protein self-assembly. Key points: • Protein crystallization screening method is successfully applied in the screening of self-assembly conditions. • This screening method can be applied on various kinds of proteins and possess a feature of low protein consumption. • This screening method is fast, high throughput, and easily implemented in an automated system. [ABSTRACT FROM AUTHOR]

A process for human influenza H1N1 virus vaccine production from Madin-Darby canine kidney (MDCK) cells using a novel packed-bed bioreactor is described in this report. The mini-bioreactor was used to study the relationship between cell density and glucose consumption rate and to optimize the infection parameters of the influenza H1N1 virus (A/New Caledonia/20/99). The MDCK cell culture and virus infection were then monitored in a disposable perfusion bioreactor (AmProtein Current Perfusion Bioreactor) with proportional-integral-derivative control of pH, dissolved O (DO), agitation, and temperature. During 6 days of culture, the total cell number increased from 2.0 × 10 to 3.2 × 10 cells. The maximum virus titers of 768 hemagglutinin units/100 μL and 7.8 × 10 50 % tissue culture infectious doses/mL were obtained 3 days after infection. These results demonstrate that using a disposable perfusion bioreactor for large-scale cultivation of MDCK cells, which allows for the control of DO, pH, and other conditions, is a convenient and stable platform for industrial-scale production of influenza vaccines. [ABSTRACT FROM AUTHOR]