Structure of the protease domain of memapsin 2 (beta-secretase) complexed with inhibitor

Memapsin 2 (beta-secretase) is a membrane-associated aspartic protease involved in the production of beta-amyloid peptide in Alzheimer's disease and is a major target for drug design. We determined the crystal structure of the protease domain of human memapsin 2 complexed to an eight-residue inhibitor at 1.9 angstrom resolution. The active site of memapsin 2 is more open and less hydrophobic than that of other human aspartic proteases. The subsite locations from S4 to S2' are well defined. A kink of the inhibitor chain at P2' and the change of chain direction of P3' and P4' may be mimicked to provide inhibitor selectivity.     

Modification of the active site of alkaline phosphatase by site-directed mutagenesis

The catalytically essential amino acid in the active site of bacterial alkaline phosphatase (Ser-102) has been replaced with a cysteine by site-directed mutagenesis. The resulting thiol enzyme catalyzes the hydrolysis of a variety of phosphate monoesters. The rate-determining step of hydrolysis, however, is no longer the same for catalysis when the active protein nucleophile is changed from the hydroxyl of serine to the thiol of cysteine. Unlike the steady-state kinetics of native alkaline phosphatase, those of the mutant show sensitivity to the leaving group of the phosphate ester.     

Plate motions and stresses from global dynamic models

Delineating the driving forces behind plate motions is important for understanding the processes that have shaped Earth throughout its history. However, the accurate prediction of plate motions, boundary-zone deformation, rigidity, and stresses remains a difficult frontier in numerical modeling. We present a global dynamic model that produces a good fit to such parameters by accounting for lateral viscosity variations in the top 200 kilometers of Earth, together with forces associated with topography and lithosphere structure, as well as coupling with mantle flow. The relative importance of shallow structure versus deeper mantle flow varies over Earth's surface. Our model reveals where mantle flow contributes toward driving or resisting plate motions. Furthermore, subducted slabs need not act as strong stress guides to satisfy global observations of plate motions and stress.     

Rearing advanced fry of major Indian carp species in recirculatory-filtering ponds at Barrackpore,West Bengal

This paper describes an experiment using a recirculatory-filtering system operating in two rectangular cemented ponds (160 and 190 m², 1.5 m deep) to rear fry (25 mm–50 mm) of the major Indian carp species Labeo rohita (Hamilton) and Catla catla (Hamilton) to fingerlings (100 mm–125 mm). These operations were concluded in both the species in 32 days at stocking densities of 0.46 million/ha and 0.55 million/ha, and showed survival rates of 96.6% and 84.4% respectively. In the presently followed practices of modern fish culturists, corresponding operations in earth ponds usually take 90 days and have a stocking density of 0.2 million/ha with survival rates more or less similar to those obtained in the recirculatory-filtering system. If followed by industry, the technique described will enable production of major Indian carp fingerlings with great saving in time, the use of water and the space occupied by the production system. These advantages greatly enhance the economic viability of rearing carp fingerling in India.     

Microencapsulation of a putative probiotic Enterobacter species,C6‐6, to protect rainbow trout,Oncorhynchus mykiss (Walbaum), against bacterial coldwater disease

Flavobacterium psychrophilum is the causative agent of bacterial coldwater disease (BCWD), which has a major impact on salmonid aquaculture globally. An Enterobacter species, C6‐6, isolated from the gut of rainbow trout, Oncorhynchus mykiss (Walbaum), has been identified as a potential probiotic species providing protection against BCWD. This study examined the effects of alginate microencapsulation on the protective efficacy of C6‐6 against BCWD in vivo when administered to rainbow trout fry orally or by intraperitoneal (IP) injection. Viable C6‐6 bacteria were microencapsulated successfully, and this process (microencapsulation) did not significantly deteriorate its protective properties as compared to the administration of non‐microencapsulated C6‐6 bacteria. Both oral and IP delivery of C6‐6 achieved significantly better protection than control treatments that did not contain C6‐6 bacteria. The highest relative percent survival (RPS) resulted from IP delivery (71.4%) and was significantly greater than the highest oral RPS (38.6%). Successful intestinal colonization was not critical to protective effects of C6‐6. The study showed that C6‐6 administration, with or without encapsulation, was a viable choice for protecting fry from BCWD especially when administered intraperitoneally.     

Enzyme‐producing bacteria isolated from fish gut: a review

Digestion of food depends on three main factors: (i) the ingested food and the extent to which the food is susceptible to the effects of digestive enzymes, (ii) the activity of the digestive enzymes and (iii) the length of time the food is exposed to the action of the digestive enzymes. Each of these factors is affected by a multitude of secondary factors. The present review highlights the experimental results on the secondary factor, enzymatic activity and possible contribution of the fish gut microbiota in nutrition. It has been suggested that fish gut microbiota might have positive effects to the digestive processes of fish, and these studies have isolated and identified the enzyme‐producing microbiota. In addition to Bacillus genera, Enterobacteriaceae and Acinetobacter, Aeromonas, Flavobacterium, Photobacterium, Pseudomonas, Vibrio, Microbacterium, Micrococcus, Staphylococcus, unidentified anaerobes and yeast are also suggested to be possible contributors. However, in contrast to endothermic animals, it is difficult to conclude the exact contribution of the gastrointestinal microbiota because of the complexity and variable ecology of the digestive tract of different fish species, the presence of stomach and pyloric caeca and the relative intestinal length. The present review will critically evaluate the results to establish whether or not intestinal microbiota do contribute to fish nutrition.     

Trophic-level modelling of the coastal waters of the northern Bay of Bengal,West Bengal,India

An ecosystem model was constructed for the northern Bay of Bengal (nBoB) using Ecopath (version 6.4.4). The model covered an area of 18,500 km². There were 32 functional groups in the model including the non-living group, detritus. Trophic levels (TLs) for individual groups ranged from 1.0 to 4.22. Ecotrophic efficiency for most of the small pelagic fishes was found to be greater than 0.7. For hilsa it was 0.853, indicating high exploitation of this fish within the system. The nBoB was estimated to be a low ascendancy area (~?19.2%) with a system overhead of 80.8%, which indicates system stability and a certain maturity. The total system throughput and the total primary production/total respiration estimated for the study area indicate that nBoB is a maturing ecosystem. The mean TL of the catch for the study area was 3.115. The results indicate that the nBoB system is still in a developing stage. The low mean TL of the catch indicates fishing practices targeting fish of lower TLs in the system. In the long run, this may cause fishing down the food web, which will eventually lead to declining catches. These results indicate that present fishing practices are unsustainable for the nBoB ecosystem.     

Effect of feeding level on growth,body composition,fatty acid profile,and nutrient accumulation in shrimp (<Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>)

A study was conducted in a recirculating aquaculture system (RAS) to assess the growth performance, body composition, fatty acid profile, and nutrient accumulation in different tissues of shrimp using two feeding levels (10 and 16 g/kg^0.8/day). The shrimp PL₂₅ was nursed in the nursing tank for 2 months and stocked in six grow out tanks (ten individuals in each 30 L tank). A commercial feed with 42.7% protein was used over a 16-h period per day. After 4 weeks, the final average weight when fed 16 g/kg^0.8/day was 9.7 g which was not significantly different from a final weight of 8.6 g achieved when feeding 10 g/kg^0.8/day. The protein and energy content increased in high feeding level whereas moisture, crude fat, and ash content decreased with feeding level (P?>?0.05). With the high feeding level, the fatty acid content increased in the eye, muscle, and whole body, with eye containing the highest concentration. The isotopic ratio of δ¹³C was enriched with feeding level in the muscle and whole shrimp whereas the ratio of δ¹³C was depleted in the viscera with feeding level. The fraction of δ¹⁵N was enriched with decreasing feeding level and highest value was found in the muscle than in the whole shrimp and viscera.     

Effect of probiotic on reproductive performance in female livebearing ornamental fish

A probiotic bacterial strain, Bacillus subtilis, isolated from the intestine of Cirrhinus mrigala (Hamilton), was incorporated in fish feed at four different concentrations (5 × 10⁸ cells g⁻², 5 × 10⁷ cells g⁻², 5 × 10⁶cells g⁻¹ and 5 × 10⁵ cells g⁻¹) and fed to four species of livebearing ornamental fish, Poecilia reticulata (Peters), Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel) and Xiphophorus maculatus (Gunther) for one year duration to observe the effect of dietary probiotic supplementation on their reproductive performance. Sixty virgin females of each species were stocked separately in circular FRP tanks (350 L) and fed diets with varying levels of probiotic cells and control feed. Broodstock performance was evaluated based on gonadosomatic index (GSI), fecundity and fry production of female broodstock. The results showed that supplementation of feed with probiotics increased significantly (P<0.05) the GSI, fecundity and fry production of spawning females and length and weight of fry in all the four species of fish. The number of dead and deformed fry were also significantly lower (P<0.05) in fish fed with the probiotic feeds. The use of higher concentration of the probiont in diet did not always lead to significantly improved reproductive performance of the spawners. Collectively, this study showed that female livebearers benefit from inclusion of probiotics in diet during their reproductive stages.     

Inhibitory effect of <Emphasis Type="Italic">Pistia</Emphasis> tannin on digestive enzymes of Indian major carps: an in vitro study

Aquatic weeds are one of the major unconventional feed ingredients tested for aquafeed formulation. Tannin content in the water lettuce, Pistia, has been quantified (26.67 mg g⁻¹; dry weight) and graded levels of which (12.5–200 μg) have been incorporated in the reaction mixtures to evaluate any change in the in vitro activity of the principal digestive enzymes from the three Indian major carps (IMC), namely rohu (Labeo rohita), catla (Catla catla) and mrigala (Cirrhinus mrigala). Result of the experiment revealed that the Pistia tannin (PT) significantly inhibit/lower the activities of the digestive enzymes from three IMCs in a dose-dependant manner, even at very low concentration. Significant variation in the reduction of the enzyme activities was noticed between the three fish species, as well as between the three enzymes studied. Among the three species studied, digestive enzymes from L. rohita were found to be the most sensitive to the PT, whereas enzymes from C. catla were found to be comparatively least affected. On the other hand, protease and lipase activities were comparatively more affected than the amylase activity. The results of the study suggest that more stress should be given on the elimination of tannin while incorporating feed ingredients of plant origin in fish diets.