The bacterial profiles of 63 grasshopper sub shrimp paste samples collected from seven typical regions around the Bohai Sea were investigated by high-throughput sequencing.
was found to be the ...prevailing species present in all the samples, and the presence of
also weakly correlated with the histamine content in the samples. Six
strains with low biogenic amine (BA)-producing ability and deficient in histamine production were identified and subjected to safety assessment. All six strains displayed weak resistance to fifteen known antibiotics as based on the
breakpoint values. None of the strains exhibited hemolytic activity or biofilm formation. All strains exhibited were able to grow on MRS agar containing 21% NaCl and expressed amine oxidase and strain-specific proteases and lipases. Most of the strains exhibited acid production at 18% NaCl. Moreover, three of the strains (designated as SG, TS, and QH) with histamine degradation ability were inoculated into separate shrimp paste samples to determine their effect on BA accumulation. The results indicated that the addition of
to shrimp pastes not only led to a significant reduction of BA content in the pastes but also improved the flavor of the pastes. Consequently, these strains may be used as potential candidates for controlling the content of histamine in fermented foods.
Cancer is a great threat of human health worldwide due to the uncontrollable spread of malignant cells throughout the body. Accurate diagnosis and targeted therapy approaches are critical factors for ...cancer treatment. Combination of therapeutic and diagnostic agents in a single nanocarrier enables to simultaneously monitor the cancer progression and tune disease therapy with minimum side effect.
Carbon dots are a novel class of small fluorescence carbon nanostructures with size less than 10 nm at least in one dimension, which exhibit excellent optical properties, larger surface area to volume ratio and low toxicity. The unique properties of carbon dots make it as an ideal carrier for incorporation of cancer targeting moieties, bio-imaging agents and antineoplastic agents in one delivery system.
An literature search was conducted using Web of Science to find out articles related to carbon dots and tumor theranostics.
Numerous applications of carbon dots in cancer theranostics have been reported during the past 10 years. This review introduces a brief history and basic fluorescent properties of carbon dots, and then discusses synthesis strategies and applications of carbon dots in biological imaging, targeted anti-cancer drug delivery, photodynamic therapy, photothermal therapy as well as gene delivery for cancer theranostics. Future directions of carbon dots in cancer theranostics are also highlighted.
, a specific spoilage microorganism, has a strong capacity to destroy food protein and lead to spoilage. The aim of this study was to evaluate the phase-dependent regulation of lux-type genes on the ...spoilage characteristics of
H4. The auto-inducer synthase gene
and a regulatory gene
of the quorum sensing systems in
H4 were knocked out to construct the mutant phenotypes. On this basis, the research found that the
and
genes had a strong positive influence on not only flagella-dependent swimming ability and biofilm formation but also the production of putrescine and cadaverine. The
gene could downregulate putrescine production. The maximum accumulation of putrescine in wild type, Δ
, Δ
and Δ
were detected at 24 h, reaching up to 695.23 mg/L, 683.02 mg/L, 776.30 mg/L and 724.12 mg/L, respectively. However, the
and
genes have a potential positive impact on the production of cadaverine. The maximum concentration of cadaverine produced by wild type, Δ
, Δ
and Δ
were 252.7 mg/L, 194.5 mg/L, 175.1 mg/L and 154.2 mg/L at 72 h. Moreover, the self-organizing map analysis revealed the phase-dependent effects of two genes on spoilage properties. The
gene played a major role in the lag phase, while the
gene mainly acted in the exponential and stationary phases. Therefore, the paper provides valuable insights into the spoilage mechanisms of
H4.
(
) is a common foodborne pathogen that leads to various diseases; therefore, we urgently need to identify different means to control this harmful pathogen in food. In this study, we monitored the ...transcriptional changes of
by RNA-seq analysis to better understand the effect of benzyl isothiocyanate (BITC) on the virulence inhibition of
and determined the bacteriostatic effect of BITC at subinhibitory concentrations. Our results revealed that, compared with the control group (SAC), the BITC-treated experimental group (SAQ_BITC) had 708 differentially expressed genes (DEGs), of which 333 genes were downregulated and the capsular polysaccharide (
) was significantly downregulated. Furthermore, we screened five of the most virulent factors of
, including the capsular polysaccharide biosynthesis protein (
), capsular polysaccharide synthesis enzyme (
), thermonuclease (
), clumping factor (
), and protein A (
), and verified the accuracy of these significantly downregulated genes by qRT-PCR. At the same time, we used light microscopy, scanning electron microscopy (SEM) and inverted fluorescence microscopy (IFM) to observe changes in biofilm associated with the
and
. Therefore, these results will help to further study the basis of BITC for the antibacterial action of foodborne pathogenic bacteria.
The
serp
gene codes for a protease that is considered to be an important factor associated with quorum sensing (QS)–based food spoilage caused by microorganisms. In this study, we evaluated the ...effect of temperature (4–37 °C) and QS inhibitors on the production of
N
-acyl-L-homoserine lactones (AHLs) and relative expression of the
luxR/I
, as well as
serp
in
Hafnia alvei
H4. Production of AHLs and expression of
luxR/I
were found to reach maximum levels at 10 °C, suggesting that the QS system of
H. alvei
H4 might have higher activity at low temperatures; similar result was also obtained for
serp
expression. Mutants of
H. alvei
H4 deficient in QS were used to identify the regulation of QS on
serp
expression. Significant reduction (
P
< 0.05) in
serp
expression was found in the mutants ∆
luxR
, ∆
luxI
, and ∆
luxR/I
, with ∆
luxI
and ∆
luxR/I
showing greater reduction than ∆
luxR
. Minimum inhibition concentrations (MIC) of Benzyl isothiocyanate and 3-Methylthiopropyl isothiocyanate for
H. alvei
H4 were determined to be 7.813 and 15.625 mM, respectively. Furthermore, the expression of
serp
, as well as that of
luxR
and
luxI
, was significantly repressed (
P
< 0.05) by the two QS inhibitors at 1/8 MIC and 1/16 MIC, indicating that these inhibitors might repress
serp
expression through affecting
luxR
and
luxI
expression in
H. alvei
H4. The findings of this study, therefore, suggested that food spoilage caused by
H. alvei
could be controlled through the application of QS inhibitors.
Biogenic amines (BAs) and microbial diversity are important factors affecting food quality and safety in fermented foods. In this study, the bacterial and fungal diversity in grasshopper sub shrimp ...paste taken at different fermentation times were comprehensively analyzed, while the pH, colony counts, salinity, total volatile base nitrogen (TVB-N) and BA contents were quantitatively determined. In addition, the correlations among the samples with respect to microbial communities and the different parameters investigated especially BAs were also established. By combining the results of spearman correlation heatmap with the contents of BAs produced by the 102 halotolerant bacteria isolated from the grasshopper sub shrimp paste, six major genera of bacteria (
,
,
,
,
, and
) were found to be positively correlated with BA production level, suggesting that these bacteria might have a strong tendency to produce BAs. Other bacteria such as
,
, and
were considered as poor BA producers. The grasshopper sub shrimp paste was characterized by a relatively high abundance of
, which was the dominant genus during the fermentation process, and it also produced a relatively high level of BAs but the spearman correlation heatmap revealed a negative correlation between
and BA level. Analysis of the species relevance network in grasshopper sub shrimp explained that the actual production of BAs by a certain strain was closely related to other species present in the complex fermentation system.
Quorum sensing (QS) is a widespread regulatory mechanism in bacteria used to coordinate target gene expression with cell density. Thus far, little is known about the regulatory relationship between ...QS and cell density in terms of metabolic pathways in
H4. In this study, transcriptomics analysis was performed under two conditions to address this question. The comparative transcriptome of
H4 wild-type at high cell density (OD
= 1.7) relative to low cell density (OD
= 0.3) was considered as growth phase-dependent manner (GPDM), and the transcriptome profile of
deletion mutant (Δ
) compared to the wild-type was considered as QS-mediated regulation. In all, we identified 206 differentially expressed genes (DEGs) mainly presented in chemotaxis, TCA cycle, two-component system, ABC transporters and pyruvate metabolism, co-regulated by the both density-dependent regulation, and the results were validated by qPCR and swimming phenotypic assays. Aside from the co-regulated DEGs, we also found that 59 DEGs, mediated by density-independent QS, function in pentose phosphate and histidine metabolism and that 2084 cell-density-dependent DEGs involved in glycolysis/gluconeogenesis and phenylalanine metabolism were influenced only by GPDM from significantly enriched analysis of transcriptome data. The findings provided new information about the interplay between two density-dependent metabolic regulation, which could assist with the formulation of control strategies for this opportunistic pathogen, especially at high cell density.
In the food industry, foodborne spoilage bacteria often live in mixed species and attach to each other, leading to changes in spoilage characteristics. Quorum sensing (QS) has been reported to be a ...regulating mechanism for food spoiling by certain kinds of bacteria. Here, the contents of biofilm, extracellular polysaccharides, and biogenic amines in the coculture system of
H4 and
ATCC13525 were significantly reduced when the QS element of
H4 was deleted, confirming that QS of
H4 is involved in the dual-species interactions. Then, transcriptomics was used to explore the regulatory mechanism at the mRNA molecular level. The deletion of the QS element decreased the transcript levels of genes related to chemotaxis, flagellar assembly, and the two-component system pathway of
H4 in the coculture system. Furthermore, a total of 732 DEGs of
ATCC13525 were regulated in the dual species, which were primarily concerned with biofilm formation, ATP-binding cassette transporters, and amino acid metabolism. Taken together, the absence of the QS element of
H4 weakened the mutual cooperation of the two bacteria in the coculture system, making it a good target for managing infection with
and
.
Foodborne illness caused by Vibrio parahaemolyticus (V. parahaemolyticus) is generally associated with the consumption of seafood. Fish and other seafood can be contaminated with V. parahaemolyticus, ...natural inhabitants of the marine, estuarine, and freshwater environment. In this study, the antibacterial activities of benzyl isothiocyanate (BITC) against V. parahaemolyticus were investigated by both transcriptomic analysis and morphological verification.
Treatment with 1/8 minimum inhibitory concentration (1/8 MIC) BITC resulted in 234 upregulated genes and 273 downregulated genes. The results validated by quantitative real-time polymerase chain reaction (qRT-PCR) revealed that the relative expression levels of the six genes VP0820, VP0548, VP2233, VPA2362, fliA and fliG were only 31.0%, 31.1%, 55.8%, 57.0%, 75.3%, and 79.9% of the control group, respectively. Among them, genes VP2233, fliA and fliG are related to flagella and VP2362 can regulate a protein relevant to biofilm formation. Morphologically, we verified that the swimming diffusion diameter of V. parahaemolyticus was significantly reduced by 14.9% by bacterial swimming ability, and biofilm formation was significantly inhibited by treatment with 1/8 MIC BITC by crystal violet quantification assay.
These results indicated that 1/8 MIC BITC had antibacterial effect on V. parahaemolyticus by inhibiting virulence gene expression related to flagella and biofilm.
Quorum sensing (QS) regulation of functional metabolites is rarely reported but a common trait of some bacteria. In this study, we found that QS promoted the extracellular accumulation of glycine and ...serine while inhibiting the extracellular accumulation of methionine in
H4. The correlation analysis of five QS signals with the above three QS-regulated amino acids suggested that these QS signals may have functional differences in amino acid regulation. The exogenous AHL add-back studies on genes involved in glycine, serine, and methionine metabolic pathway highlighted that
-octanoyl-l-homoserine lactone (C8-HSL) downregulated the expression of
/
genes involved in the succinate to malate pathway, thereby reducing the metabolic flux of the tricarboxylic acid (TCA) cycle as an amino acid metabolism platform. Further in-depth research revealed that the QS system promoted the conversion of folate to tetrahydrofolate (THF) by positively regulating the expression of
and
, thus impairing the ability of folate to promote methionine accumulation. Moreover, folate positively regulated the expression of the QS signal synthesis gene
, promoting the synthesis of QS signals, which may further enhance the influence of the QS system on amino acid metabolism. These findings contribute to the understanding of amino acid metabolism regulated by QS and provide new perspectives for accurate control of metabolic regulation caused by QS.IMPORTANCEAs one of the important regulatory mechanisms of microorganisms, quorum sensing (QS) is involved in the regulation of various physiological activities. However, few studies on the regulation of amino acid metabolism by QS are available. This study demonstrated that the LuxI-type QS system of
H4 was involved in the regulation of multiple amino acid metabolism, and different types of QS signals exhibited different roles in regulating amino acid metabolism. Additionally, the regulatory effects of the QS system on amino acid metabolism were investigated from two important cycles that influence the conversion of amino acids, including the TCA cycle and the folate cycle. These findings provide new ideas on the role of QS system in the regulation of amino acid metabolism in organisms.
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