Advances on fluorescence chemosensors for selective detection of water.

Water, although an important part of everyday life, is acts as one of the most significant contaminants in various applications such as biomedical monitoring, chemical production, petroleum-based fuel and food processing. In fact, the presence of water in other solvents is a huge concern. For the quantification of trace water content, different methods such as Karl-Fischer, electrochemical, nuclear magnetic resonance, chromatography, and thermogravimetric analysis have been used. Although every technique has its own benefit, each one suffers from several drawbacks that include high detection costs, lengthy procedures and specialized operations. Nowadays, the development of fluorescence-based chemical probes has become an exciting area of research for the quick and accurate estimation of water content in organic solvents. A variety of chemical processes such as hydrolysis reaction, metal ions promoted oxidation reaction, suppression of the -C═N isomerization, protonation and deprotonation reactions, and molecular aggregation have been well researched in the last few years for the fluorescent detection of trace water. These chemical processes eventually lead to different photophysical events such as aggregation-induced emission (AIE), aggregation-induced emission enhancement (AIEE), aggregation-caused quenching (ACQ), fluorescent resonance energy transfer (FRET), charge transfer, photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT) that are responsible for the detection. This review presents a summary of the fluorescence-based chemosensors reported in recent years. The design of water sensors, sensing mechanisms and their potential applications are reviewed and discussed.

A Formyl Chromone Based Schiff Base Derivative: An Efficient Colorimetric and Fluorescence Chemosensor for the Selective Detection of Hg2+ Ions.

A novel chromone-based Schiff base L was designed and synthesized by condensing an equimolar amount of 3-formyl chromone and 2,4-dinitro phenyl hydrazine. Schiff base L was developed as a potent colorimetric and fluorescent molecular probe to recognize Hg2+ ions over other competitive metal ions. In the presence of Hg2+, Schiff base L displays a naked-eye detectable color change under day and UV365 nm light. Various UV-Vis and fluorescence studies of L were performed in the absence and presence of Hg2+ to determine the sensitivity and the sensing mechanism. With high selectivity and specificity, the detection limit and association constant of L for Hg2+ were estimated at 1.87 µM and 1.234 × 107 M-1, respectively. The developed sensor L was applied to real soil samples for the detection of Hg2+.

Pyrene-based fluorescent chemosensor for rapid detection of water and its applications.

This manuscript introduces a pyrene-based Schiff base L by reacting pyrenecarboxaldehyde with 2-aminothiazole in equimolar ratio. The ligand L was characterized by various spectral data and single crystal. The water sensing ability of L was examined in different organic solvents. The weakly emissive L in DMSO showed a fluorescence enhancement upon the addition of water. The water-induced fluorescence enhancement of L was occurred due to the combined effect of aggregation-induced emission (AIE) phenomenon and suppression of photo-induced electron transfer (PET) process. Using L, the water in DMSO can be detected down to 0.50 wt% with a quantification limit of 1.52 wt%. The analytical novelty of the developed sensor L was validated by detecting moisture in a variety of raw food products.

Rapid Colorimetric and Fluorometric Discrimination of Maleic Acid vs. Fumaric Acid and Detection of Maleic Acid in Food Additives.

An anthracene thiazole based Schiff base L was synthesized and employed for fluorescence switch-on detection of maleic acid in aqueous DMSO. The non-fluorescent L (10-5 M) showed an instantaneous and selective fluorescence enhancement at 506 nm upon interaction with maleic acid (10-5 M). Other potential carboxylic acids (10-5 M), such as malic acid, citric acid, acetic acid, cinnamic acid, tartaric acid, succinic acid, fumaric acid, oxalic acid and malonic acid failed to alter the chromo-fluorogenic properties of L. Probe L can be employed to detect maleic acid down to 2.74 × 10-6 M. The probe L showed good linearity from 2.97 to 6.87 µM. Analytical utility of L was examined by detecting maleic acid in various food additives and drosophila larvae.

Temperature alters the oxidative and metabolic biomarkers and expression of environmental stress-related genes in chocolate mahseer (Neolissochilus hexagonolepis).

Long-term acclimation temperature effects on biomarkers of oxidative stress, metabolic stress, expression of heat shock proteins (Hsps), and warm-temperature acclimation related 65-kDa protein (Wap65) were evaluated in the threatened chocolate mahseer (Neolissochilus hexagonolepis). Fifteen-day-old larvae were acclimated to different water temperatures (15, 19, 23-control group, 27, and 31 °C) for 60 days prior to the sampling for quantification of mRNA, enzyme, nitric oxide, and malondialdehyde (MDA) content. Acclimation to 31 °C increased the basal mRNA level of glutathione S-transferase alpha 1 (GSTa1), and activities of catalase (CAT), glutathione reductase (GR), and GST enzymes and but downregulated the expression of superoxide dismutase 1 (SOD1) in the whole-body homogenate. Other antioxidant genes, i.e., CAT and GPx1a, were unaffected at 31 °C, and nitric oxide (NO) concentration was significantly lower. In contrast, fish acclimated to 15 °C showed an upregulated transcript level of all the antioxidant genes and no significant difference in the CAT, GR, and GST enzymes. Activities of the metabolic enzymes, aspartate transaminase (AST) and alanine transaminase (ALT), were significantly lower at 15 °C. The expression of Hsp47 was upregulated at both 15 and 31 °C groups, whereas Hsp70 was elevated at 27 and 31 °C groups. Wap65-1 transcription did not show significant variation in treatment groups compared to control. Fish in the high (31 °C) and low-temperature (15 °C) acclimation groups were capable of maintaining oxidative stress by modulating their antioxidant transcripts, enzymes, and Hsps.

Protein interactions, molecular docking, antimicrobial and antifungal studies of terpyridine ligands.

Resistance to antibiotics/antibacterials/antifungals in pathogenic microbes has been developing over the past few decades and has recently become a commonplace public-health peril. Thus, alternative nontoxic potent antibiotic agents are covertly needed to control antibiotic-resistant outbreaks. In an effort to combat the challenges posed by the co-occurrence of multidrug resistance, two terpyridine ligands 4'-(4-N,N'-dimethylaminophenyl)-2,2':6',2″-terpyridine (L1) and 4'-(4-tolyl)-2,2':6',2″-terpyridine (L2) have been designed, prepared and confirmed their structure by spectral studies. Thereafter, antimicrobial assay was performed against gram positive and negative bacterial strains along with fungal strains. Both compounds L1 and L2 exhibited remarkable inhibitory activities against bacteria, Escherichia coli and Staphylococcus aureus at MIC values 6.25 and 3.125 µg/ml, respectively. In addition, in silico molecular docking studies were ascertained with bacterial DNA gyrase and fungal demethylase. Furthermore, both L1 and L2 could bind Bovine Serum Albumin (BSA) protein and binding interaction has been studied with the help of UV-Visible and fluorescence spectroscopy. While fluorescence of BSA unperturbed in the presence of L2, an addition of L1 to the solution of BSA resulted significant quenching. The binding constant calculations at different temperature confirmed that the fluorescence quenching between BSA and L1 is predominantly static in nature. The toxicity of L1 and L2 was checked using Drosophila melanogaster. The toxicity analysis suggest both the dyes are non-cytotoxic in nature.Communicated by Ramaswamy H. Sarma.

Computational analysis and functional characterisation of Tor putitora toll-like receptor 4 with the elucidation of its binding sites for microbial mimicking ligands.

In the current study, full-length Toll-like receptor 4 (TLR4) cDNA was cloned and characterised in Tor putitora, an important fish inhibiting Himalayan rivers. The complete coding sequence of TpTLR4 is 2457 bp with nine key structural domains, including six leucine-rich repeats (LRRs). The phylogenetic tree revealed that TpTLR4 showed the closest relationship with TLR4 of Cyprinus carpio (96%), Labeo rohita (91%) and Megalobrama amblycephala (88%), all belonging to the Cyprinidae family. CELLO2GO tool revealed that TpTLR4 protein is highly localised in the plasma (67.7%), and the protein has a strong association with myeloid differentiation primary response 88 (MYD88) followed by Tumor necrosis factor receptor-associated factor (TRAF) family. In the toll-interleukin-1 receptor (TIR) domain of TpTLR4, the proline is replaced by the alanine amino acid, thus may give plasticity to the receptor to recognise both bacterial and viral ligands. Molecular docking has revealed that TpTLR4 showed the strongest affinity towards poly (I:C) with the binding energy of -6.1 kcal/mol and five hydrogen bonds among all ligands. Based on our molecular docking results, it can be presumed that TpTLR4 can sense bacterial, fungal and viral molecular patterns with binding sites mainly present in the TpTLR4 LRR9 motif, which spans between 515 and 602 amino acids. Tor putiora TLR4 transcript was ubiquitously expressed in all the tested fish tissues. Although, transcript level was found to be highest in blood and spleen followed by the kidney. The TpTLR4 transcripts showed peak expression in spleen and kidney at 12 h post-injection (hpi) (p < 0.05) of poly (I:C). The constitutive expression of TpTLR4 in various tissues, up-regulation in different tissues and strong binding affinities with poly (I:C) indicate that TpTLR4 may play an essential role in sensing pathogen-associated molecular patterns (PAMPs), particularly of viral origin.

Tools and techniques for rational designing of antimicrobial peptides for aquaculture.

Fisheries and aquaculture industries remain essential sources of food and nutrition for millions of people worldwide. Indiscriminate use of antibiotics has led to the emergence of antimicrobial-resistant bacteria and posed a severe threat to public health. Researchers have opined that antimicrobial peptides (AMPs) can be the best possible alternative to curb the rising tide of antimicrobial resistance in aquaculture. AMPs may also help to achieve the objectives of one health approach. The natural AMPs are associated with several shortcomings, like less in vivo stability, toxicity to host cell, high cost of production and low potency in a biological system. In this review, we have provided a comprehensive outline about the strategies for designing synthetic mimics of natural AMPs with high potency. Moreover, the freely available AMP databases and the information about the molecular docking tools are enlisted. We also provided in silico template for rationally designing the AMPs from fish piscidins or other peptides. The rationally designed piscidin (rP1 and rp2) may be used to tackle microbial infections in aquaculture. Further, the protocol can be used to develop the truncated mimics of natural AMPs having more potency and protease stability.

Clinical signs, lethal dose and histopathological lesions in grass carp, Ctenopharyngodon idella experimentally infected with Edwardsiella tarda.

An experiment was conducted to study the lethal dose (LD50-96h) and histopathological changes occurring in several organs of grass carp challenged with different concentrations of Edwardsiella tarda. The healthy grass carps were challenged with the bacterial suspension of 106,107, 108, 109 and 1010 CFU ml-1. The study demonstrated that the lethal dose (LD50-96h) of E. tarda for grass carp is 1.3 × 109 CFU ml-1. The infected fish showed abnormal swimming behavior, slower movements, skin necrosis, hemorrhages, and open lesion on the fontanelle of the frontal bone of the skull during the initial phase of infection. About 60% of the fish which received the bacterial suspension of 1010 CFU ml-1 died within 24 h of infection. The histopathological examination of the infected tissue section demonstrated the severe damages in the internal organs. In gills, oedema, secondary lamellae fusion, and hyperplasia of basal epithelial lining between secondary lamellae were reported. The microscopic observation showed the disruption of submucosa to the mucosa, which finally led to degenerative changes in the intestine, necrosis of hepatocytes and infiltration of red blood cells in the liver. The tubular disintegration in kidney and loss of capsular boundary of red pulp in spleen were also reported. In conclusion, the result indicates that the infection caused by E. tarda can cause severe damages and alterations in grass carp tissues and potential mass mortality. Moreover, The bacteria isolated from the mobribund fish was characterized by biochemical tests and expression of five critical virulence genes like citC, fimA, gadB, mukF and gyrB were detected from the microorganism. The study aims to provide a research foundation for further studies on the susceptibility and pathological changes of grass carp induced by E. tarda infection.

Spawning substrate preference and spawning behavior of chocolate mahseer, Neolissochilus hexagonolepis.

Captive breeding programs for Neolissochilus hexagonolepis are essential for population restoration. To develop an efficacious method for enhancing N. hexagonolepis spawning in captivity, there was examination of: (1) different types of spawning substrate and (2) area of spawning in the substrate. The study was conducted to describe spawning behavior of males and females. There was a choice of three substrates in which to spawn: gravel, small cobble, and coarse sand. There was preferential choosing of gravel followed by cobble with there being no use of sand for spawning. Behavior of N. hexagonolepis included preparation of a spawning pit by females, a behavior that has not been previously ascertained for cyprinids. Males expressed courting behaviors, including chasing, nudging, and quivering. Courting males expressed aggressive behaviors towards other males. Results from the present study are the first on the volitional spawning of N. hexagonolepis in captivity using spawning substrate. It was further revealed that using a gravel substrate tray would also be a feasible approach for egg production. Mean total eggs per female and mean fertilized eggs collected were less when there was siphoning used for egg collections in the preference study. Hence, stripping was implemented to increase the egg collection when spawning behaviors were observed. Total eggs collected were 40,540 with 3685 eggs per female, 90.3% fertilization rate, 82.8% hatching rate, and 97.4% free-swimming larvae survival rate. The implications of this study could be beneficial for enhancing the natural population through environmental management and developing a viable egg production technique in captivity.

Lethal dose and histopathological alterations induced by Aeromonas salmonicida in experimentally challenged common carp, Cyprinus carpio.

Aeromonas salmonicida is the obligate pathogen of fishes having zoonotic potential. It is reported to cause considerable losses in world aquaculture. The current study has successfully demonstrated the induction of histopathological lesions in experimentally infected common carp. In the current study, the lethal concentration (LD50-96 h) of typical A. Salmonicida for common carp was found to be 1.5 × 107CFU mL-1. About 40% and 60% fish mortalities occurred after 72 h in the groups inoculated with 107 and 108 CFU mL-1 bacterial suspension, respectively. The fish challenged with A. salmonicida showed symptoms like abnormal swimming behaviour, lethargy, intra-abdominal fluid, haemorrhages on the ventral side of the body, vent and fins. The signs proceeded with the death of fish. In the histological sections, severe pathological alterations were reported in the tissue sections of internal organs. The microscopic observation showed sinusoidal and large blood vessel congestion in the liver, profuse haemorrhage, necrosis and infiltration of blood cells in the internal organs. The tubular architecture was lost with the infiltration of leucocytes in the kidney. In gills, more intense and prominent lamellar fusion was observed with leucocytic infiltration, telangiectasia and hyperplasia of lamellar epithelial cells. In summary, we have experimentally induced the typical A. salmonicida infection in common carp. The study will provide a research foundation for further studies on the host-pathogen interaction, therapeutics and epidemiology of A. salmonicida.

Effects of rearing temperature on egg incubation, growth, standard metabolic rate, and thermal tolerance of chocolate mahseer, Neolissochilus hexagonolepis.

The present study was aimed to assess the effect of temperatures on egg incubation, growth, standard metabolic rate (SMR), and thermal tolerance of a near threatened Himalayan hill stream chocolate mahseer (Neolissochilus hexagonolepis). For the hatching study, eggs were incubated in four temperatures (17, 20, 23, and 26 °C). The total hatching and free-swimming larvae percentage were higher at 23 °C (p < 0.05). Experiment I (for validation of the CTmax method) was carried out by incubating eggs at 17 °C and 23 °C. The CTmax was estimated in response to different warming rates (1-18°C h-1), acclimation temperatures (17 and 23°C), and the age of fishes (8, 15, 35 dph). The results suggested that a warming rate of 18°C h-1 could be used for the thermal tolerance study of yolk-sac larvae (8 dph) and 35 dph larvae, but for free-swimming larvae (15 dph) up to 3°C h-1 is suitable. Experiment II (for growth, SMR and thermal tolerance) was carried by acclimatizing 15 dph larvae in five temperatures (15, 19, 23, 27, and 31 °C) for 60 days. The mean growth rate increased with the increase in temperature from 15°C to 27°C (1.30-3.58% day-1) and decreased at 31°C. The mean SMR of the chocolate mahseer in the above acclimation temperatures was ranged from 1.14 ± 0.36 to 2.81 ± 0.15 µgO2h-1mg-1 and were significantly different (p < 0.01). The Q10 with the SMR of the fish suggested the preferred temperature ranged between 23 and 27 °C, and the optimum temperature for growth (ToptG) was estimated to be 25 °C. Chocolate mahseer is an eurythermal species which is advantageous for aquaculture practices due to its wide thermal tolerance zone (411.68°C2 in 15 to 31 °C acclimation temperature range) and high ARR values (0.49 - 0.54).

Anti-oomycetes and immunostimulatory activity of natural plant extract compounds against Saprolegnia spp.: Molecular docking and in-vitro studies.

This study aimed to investigate the effectiveness of five natural plant extract compounds Curcumin (CUR); Eugenol (EUG), Cinnamaldehyde (CIN), Stigmasterol (ST) and Morin (MOR), on two species of Saprolegnia; Saprolegnia parasitica and S. australis. Selective compounds were screened for the minimum inhibitory concentration, first for anti-oomycetes activity and then mycelium growth inhibition, spore germination inhibition and colonisation test. Nitric oxide production and myeloperoxidase activity of the compounds were tested in head kidney leukocytes of rainbow trout, Oncorhynchus mykiss to assess the immunostimulatory potential. Molecular docking of effective compounds was carried out with effector proteins of S. parasitica to investigate the target binding sites. Among all, CUR could completely inhibit zoospore production and significantly (p ≤ .05) inhibit hyphal growth at 16 mg l-1 against S. parasitica and S. australis. CIN at the concentration of 50 mg l-1 completely inhibited hyphal growth of both Saprolegnia spp., although the zoospore production of S. parasitica and S. australis was reduced at 25 mg l-1 and 10 mg l-1. In the case of EUG, significant inhibition of the hyphal growth and germination of S. parasitica zoospores was observed at 50 mg l-1. ST and MOR did not show antioomycetes activity. The molecular docking results were consistent with in vitro studies, possibly due to the binding with the vital proteins (Plasma membrane ATPase, V-type proton ATPase, TKL protein kinase, Host targeting protein 1) of S. parasitica and ultimately inhibiting their activity. CUR and CIN showed increased nitric oxide production at the highest concentration of 250 and 256 mg l-1 but the value was not significant (p ≤ .05) with control. CUR showed significantly higher peroxidase activity (p ≤ .05) at a concentration of 256 mg l-1 though values were significantly similar with concentration from 16 to 128 mg l-1. The nitric oxide and total peroxidase activity of rainbow trout leukocytes in the case of CIN showed a significant difference only at 250 mg l-1 against the control. The results conclude that CUR, CIN showed the better anti-Saprolegnia activity and could be used as phyto-additives in aquaculture. Among all, the inclusion of CUR as phyto-additives will provide additional immunostimulatory activity.