Structural-functional characterization of recombinant Apolipoprotein A-I from Labeo rohita demonstrates heat-resistant antimicrobial activity Abstract Apolipoprotein A-I is an anti-inflammatory, antioxidative, cardioprotective, anti-tumorigenic, and anti-diabetic in mammals. Apolipoprotein A-I also regulates innate immune defense mechanisms in vertebrates and invertebrates. Apolipoproteins A-I from mammals and several teleosts display antibacterial activities against Gram negative and Gram positive bacteria. The present study describes strategies to obtain high amounts of soluble purified recombinant Apolipoprotein A-I of Labeo rohita, an Indian major carp (rLrApoA-I). The study also reports its detailed structural and functional characterization i.e. antimicrobial activity against a number of important marine and fresh water bacterial pathogens. The rLrApoA-I was expressed in Escherichia coli BL21(DE3) pLysS expression host as a soluble protein under optimized conditions. The yield of purified rLrApoA-I was ~ 75 mg/L from soluble fraction using metal ion affinity chromatography. The authenticity of the rLrApoA-I was confirmed by MALDI-TOF-MS analysis. The secondary structure analysis showed rLrApoA-I to be predominantly alpha helical, an evolutionary conserved characteristic across mammals and teleosts. The purified rLrApoA-I exhibited antimicrobial activity as evident from inhibition of growth of a number of bacteria namely Aeromonas hydrophila, A. liquefaciens, A. culicicola, A. sobria, Vibrio harveyi, V. parahaemolyticus and Edwardsiella tarda in a dose–dependent manner. Minimum bactericidal concentration for A. liquefaciens, A. culicicola, and A. sobria, was determined to be 25 μg/ml or 0.81 μM whereas for A. hydrophila, E. tarda, V. parahaemolyticus and V. harveyi, it was determined to be 100 μg/ml or 3.23 μM. These data strongly suggest that recombinant ApoA-I from Labeo rohita could play a role in primary defense against fish pathogen. Further, at temperature ≥ 55 °C, though a loss in secondary structure was observed, no effect on its antibacterial activity was observed. This is of significance as the antibacterial activity is not likely to be lost even if the protein is subjected to high temperatures during transport.

Preparation of the inactivated Newcastle disease vaccine by plasma activated water and evaluation of its protection efficacy Abstract Vaccination has been regarded as the most effective way to reduce death and morbidity caused by infectious diseases in the livestock industry. In this study, plasma activated water (PAW) was introduced to prepare the inactivated Newcastle disease vaccine. Humoral immune response was tested by hemagglutination inhibition (HI) assay and enzyme-linked immunosorbent assay (ELISA). In addition, cell-mediated immune response was evaluated by lymphocyte proliferation assay and flow cytometry. The results demonstrated that the vaccine prepared by PAW at appropriate volume ratio could induce similar antibody titers in specific pathogen-free (SPF) chickens compared with the formaldehyde-inactivated vaccine. The challenge experiment further confirmed that the vaccine prepared by PAW conferred solid protection against virulent NDV. Moreover, it was found that the vaccine could promote the proliferation of lymphocytes and stimulate cell-mediated immunity of SPF chickens. Furthermore, analysis of electron spin resonance (ESR) spectroscopy and physicochemical properties of PAW suggested reactive oxygen and nitrogen species (RONS) played an essential role in the virus inactivation. Therefore, this study indicated that NDV treated by PAW in an appropriate ratio retained immunogenicity on the premise of virus inactivation. PAW as a promising strategy could be used to prepare inactivated vaccine for Newcastle disease.

Correction to: Structural basis for a highly (S)-enantioselective reductase towards aliphatic ketones with only one carbon difference between side chain The original version of this article contains error for some of the authors corrections were not included during correction stage

Structural basis for a highly ( S )-enantioselective reductase towards aliphatic ketones with only one carbon difference between side chain Abstract Aliphatic ketones, such as 2-butanone and 3-hexanone, with only one carbon difference among side chains adjacent to the carbonyl carbon are difficult to be reduced enantioselectively. In this study, we utilized an acetophenone reductase from Geotrichum candidum NBRC 4597 (GcAPRD) to reduce challenging aliphatic ketones such as 2-butanone (methyl ethyl ketone) and 3-hexanone (ethyl propyl ketone) to their corresponding (S)-alcohols with 94% ee and > 99% ee, respectively. Through crystallographic structure determination, it was suggested that residue Trp288 limit the size of the small binding pocket. Docking simulations imply that Trp288 plays an important role to form a C-H⋯π interaction for proper orientation of ketones in the pro-S binding pose in order to produce (S)-alcohols. The excellent (S)-enantioselectivity is due to a non-productive pro-R binding pose, consistent with the observation that the (R)-alcohol acts as an inhibitor of (S)-alcohol oxidation.

Regulatory and evolutionary roles of pseudo γ-butyrolactone receptors in antibiotic biosynthesis and resistance Abstract Bacteria modulate their physiological behavior by responding to various signal molecules. The signals are received by cognate receptors, which usually mediate transcriptional regulation. Streptomyces employ γ-butyrolactones (GBLs) and cognate GBL receptors (GblRs) to regulate secondary metabolism and morphological development. However, there are additional transcriptional regulators called pseudo GblR regulators, which cannot bind GBLs and are not directly associated with GBL synthase. The pseudo GblR regulators may act as transcriptional repressors and respond to antibiotic signals. They play regulatory roles in coordination of antibiotic biosynthesis by connecting the hormone feed-forward loops and the antibiotic feedback loops. As the TetR family members, they might also have evolutionary roles between the transcriptional regulators of quorum sensing and antibiotic resistance. Understanding the regulatory and evolutionary roles of the pseudo GblR family would be helpful for fine-tuning regulation of antibiotic biosynthesis and resistance.

The gut microbiota: a new perspective on the toxicity of malachite green (MG) Abstract Gut microbiome critically contributes to host health status. Thus, investigating the relationship between the gut microbiome and toxic chemicals is a hot topic in toxicology research. Exposure to malachite green (MG) has been linked to various health disorders. Thus, exploring the gut microbiota changes in response to MG would provide a new perspective on the toxicity effects of this chemical substance. MG exposure resulted in the significantly lower alpha diversity (Mann–Whitney U test, z = − 6.83, p = 0.00) but higher beta diversity (Mann–Whitney U test, z = − 1.98, p = 0.04) of gut microbiota, and significantly decreased ecosystem stability (alpha and beta variability; Mann–Whitney U test, all p < 0.05) of gut microbial communities. Gut bacterial networks showed that the interactions became more complex and stronger after MG exposure, which could decrease the stability of the network. Changes in gut microbiota composition were mainly reflected in the enrichment of opportunistic bacteria (i.e., Aeromonas and Vibrio) and the depression of fermentative bacteria (i.e., Bacteroides and Paludibacter). MG exposure leads to a significantly increased gut permeability (lipopolysaccharide-binding protein; Mann–Whitney U test, z = − 6.92, p = 0.00), which could reduce the host selective pressures on particular bacterial species (such as members in Aeromonas and Vibrio). This result was further supported by the weakened importance of a deterministic microbial assembly after MG exposure. All these findings indicated that MG exposed fishes might have more possibilities to be infected, as demonstrated by the enrichment of opportunistic pathogenic bacteria, high-level immune responses, and increased gut permeability. These findings greatly improve our understanding of the toxicity effects of MG.

How to accurately assess surfactant biodegradation-impact of sorption on the validity of results Abstract Surfactants not only are widely used in biotechnological processes but also constitute significant contaminants of the modern world. Among many reports, there is a shortage of works which summarize the issue of surfactant sorption to biomass in a way that would elucidate the biological factors for analysts and analytical factors for microbiologists. The main factor, which is not as obvious as one would expect, is associated with the susceptibility of analytical approaches to errors resulting from incorrect handling of biomass. In case of several publications reviewed in the framework of this study, it was not possible to establish whether the decrease of the analytical signal observed by the authors actually resulted from biodegradation of the surfactant. This review emphasizes the necessity to consider the possibility of surfactant sorption to microbial cells, which may result in significant detection errors as well as conceptual inconsistency. In addition, a reference study regarding representative surfactants (cationic, anionic and non-ionic) as well as yeast, Gram-negative, Gram-positive bacteria, and activated sludge was provided to highlight the possible errors which may arise from disregarding sorption processes when determining degradation of surfactants. This particularly applies to systems which include ionic surfactants and activated sludge as sorption may account for 90% of the observed depletion of the surfactant. Therefore, a systematic approach was proposed in order to improve the credibility of the obtained results. Finally, the need to employ additional procedures was highlighted which may be required in order to verify that the decrease of surfactant concentration results from biodegradation processes.

Specific affinity and relative abundance of methanogens in acclimated anaerobic sludge treating low-strength wastewater Abstract Kinetic parameters affecting effluent water quality including half saturation constant (Ks), maximum specific growth rate (μmax), and specific affinity (\( {a}_A^0 \), defined as μmax/Ks) were investigated using three types of anaerobic sludge (raw anaerobic digestion sludge referred to as unacclimated sludge, unacclimated sludge after endogenous decay, and sludge acclimated to low-strength wastewater in an anaerobic membrane bioreactor (AnMBR) for 360 days). Long-term acclimation to low-strength wastewater resulted in sludge with high specific affinity (1.6 × 10−3 L/mg COD/day for acclimated sludge compared to 4.1 × 10−4 L/mg COD/day for unacclimated sludge). The μmax values for unacclimated sludge and acclimated sludge were 0.08 and 0.07 day−1, respectively. The Ks values for unacclimated sludge and acclimated sludge were 194 ± 81 mg COD/L and 45 ± 13 mg COD/L, respectively. Although the Ks of unacclimated sludge after endogenous decay increased to 772 ± 74 mg COD/L, μmax increased to 0.35 day−1 as well, resulting in no statistically significant difference of \( {a}_A^0 \) between the two types of unacclimated sludge. Overall, \( {a}_A^0 \) is a better indicator than μmax or Ks alone for determining effluent water quality, as effluent substrate concentration is approximately inversely proportional to the specific affinity. 16S rRNA sequencing data analysis indicated a high abundance (85.8% of total archaea) of Methanosaeta in the microbial community after long-term acclimation. High \( {a}_A^0 \) associated with the enrichment of Methanosaeta appears to ensure successful anaerobic treatment of low-strength wastewater.

Correction to: Sucrose isomers as alternative sweeteners: properties, production, and applications There is an error in the original publication of this paper. Figures 1 and 2 have been interchanged. The corrected version of these figures is shown below:

Metabolic profiling of cold adaptation of a deep-sea psychrotolerant Microbacterium sediminis to prolonged low temperature under high hydrostatic pressure Abstract The most wide-spread “hostile” environmental factor for marine microorganisms is low temperature, which is usually accompanied by high hydrostatic pressure (HHP). Metabolic mechanisms of marine microorganisms adapting to prolonged low temperature under HHP remain to be clarified. To reveal the underlying metabolic mechanisms, we performed NMR-based metabolomic analysis of aqueous extracts derived from a psychrotolerant Microbacterium sediminis YLB-01, which was isolated from deep-sea sediment and possess great biotechnology potentials. The YLB-01 cells were firstly cultivated at the optimal condition (28 °C, 0.1 MPa) for either 18 h (logarithmic phase) or 24 h (stationary phase), then continually cultivated at either 28 °C or 4 °C under HHP (30 MPa) for 7 days. The cells cultivated at low temperature, which experienced cold stress, were distinctly distinguished from those at normal temperature. Cold stress primarily induced metabolic changes in amino acid metabolism and carbohydrate metabolism. Furthermore, the logarithmic and stationary phase cells cultivated at low temperature exhibited distinct metabolic discrimination, which was mostly reflected in the significantly disturbed carbohydrate metabolism. The logarithmic phase cells displayed suppressed TCA cycle, while the stationary phase cells showed decreased pyruvate and increased lactate. In addition, we performed transcriptome analysis for the stationary phase cells to support the metabolomic analysis. Our results suggest that the cold adaptation of the psychrotroph YLB-01 is closely associated with profoundly altered amino acid metabolism and carbohydrate metabolism. Our work provides a mechanistic understanding of the metabolic adaptation of marine psychrotrophs to prolonged low temperature under HHP.