Escherichia coli rap mutants do not support vegetative growth of bacteriophage X and die upon transcription of X DNA bar sites. Bacteria harbouring a pth(ts) mutation synthesize thermosensitive peptidyl-tRNA hydrolase (Pth) and die at 42°C from a defect in protein synthesis. We present evidence that both rap and pth(ts) mutations affect the same gene: (i) peptidyl-tRNA hydrolase activity was found to be defective in rap mutants; (ii) at a threshold temperature, pth cells, like rap mutants, prevented X growth and were killed by transcription of cloned bar sites; (iii) sequencing a 1600 bp DNA fragment comprising both loci revealed an ORF located within the limits set by a complementation analysis and encoding a putative polypeptide of 21 kDa; (iv) cloning and sequencing of rap and pth(ts) mutant DNAs both revealed single nucleotide transitions from the wild type ORF sequence, resulting in Argl34 to His and GlylOl to Asp changes respectively. Analysis of plasmid-directed proteins identified a polypeptide of -21 kDa; the Nterminal sequence, amino acid composition and isoelectric point of this protein match those expected from the ORF nucleotide sequence. We propose that Pth activity, directly or indirectly, is the target for X bar RNA leading to rap cell death. Key words: bacteriophage X bar inhibitionlEscherichia coli rap mutants/peptidyl-tRNA hydrolase/protein synthesis inhibition/sequence of pth
The development of digestive enzymes during the early ontogeny of the Mayan cichlid (Cichlasoma urophthalmus) was studied using biochemical and electrophoretic techniques. From yolk absorption (6 days after hatching: dah), larvae were fed Artemia nauplii until 15 dah, afterward they were fed with commercial microparticulated trout food (45% protein and 16% lipids) from 16 to 60 dah. Several samples were collected including yolk-sac larvae (considered as day 1 after hatching) and specimens up to 60 dah. Most digestive enzymes were present from yolk absorption (5-6 dah), except for the specific acid proteases activity (pepsin-like), which increase rapidly from 8 dah up to 20 dah. Three alkaline proteases isoforms (24.0, 24.8, 84.5 kDa) were detected at 8 dah using SDS-PAGE zymogram, corresponding to trypsin, chymotrypsin and probably leucine aminopeptidase enzymes, and only one isoform was detected (relative electromobility, Rf = 0.54) for acid proteases (pepsin-like) from 3 dah onwards using PAGE zymogram. We concluded that C. urophthamus is a precocious fish with a great capacity to digest all kinds of food items, including artificial diets provided from 13 dah.
The feasibility of substituting soybean meal for ¢shmeal diets for juvenile white shrimp Litopenaeus schmitti (0.35 AE 0.01g) was evaluated, and an adequate substitution level was determined. Five diets were evaluated using 46%, 59%, 75%, 88% and 100% substitution levels. Pellet water stability was signi¢cantly a¡ected by dietary soybean content (Po0.05). Increased soybean content produced lower pellet stability, ranging from a dry matter loss of 142 2% after a 2-h immersion, and 20^33% after an 8-h immersion. After 52 days, signi¢cant di¡erences (Po0.05) were found in shrimp weight, feed conversion ratio and protein e⁄ciency ratio. The values were 0.64^1.06 g, 2.8^7.9 and 0.45^1.21, respectively, for the three measurements. Overall, better results were obtained with diets where soybean meal was substituted for ¢shmeal up to 75%. The 100% soybean meal diet resulted in poor growth performance of shrimp. Survival rates were acceptable for all treatments (90% or higher) and no signi¢cant di¡erences were found in survival between treatments. Regression analysis using the broken-line methodology indicated that 76.5 AE 2% is an optimum soybean substitution level in diets that contained ¢shmeal and soybean as the major protein sources for growout of juvenile white shrimp. Ã Means of triplicate samples AE SE. Values in the same row with di¡erent superscript letters are signi¢cantly di¡erent.Aquaculture Research, 2007, 38, 689^695 Substitution of ¢shmeal with soybean meal J S Alvarez et al.
Spotted sand bass Paralabrax maculatofasciatus is a potential aquaculture species in Northwest Mexico. In the last few years it has been possible to close its life cycle and to develop larviculture technology at on pilot scale using live food, however survival values are low (11%) and improvements in growth and survival requires the study of the morpho-physiological development during the initial ontogeny. In this research digestive activity of several enzymes were evaluated in larvae, from hatching to 30 days after hatching (dah), and in live prey (rotifers and Artemia), by use of biochemical and electrophoretic techniques. This paper, is the first of two parts, and covers only the biochemical analysis. All digestive enzyme activities were detected from mouth opening; however the, maximum activities varied among different digestive enzymes. For alkaline protease and trypsin the maximum activities were detected from 12 to 18 dah. Acid protease activity was observed from day 12 onwards. The other digestive enzymes appear between days 4 and 18 after hatching, with marked fluctuations. These activities indicate the beginning of the juvenile stage and the maturation of the digestive system, in agreement with changes that occur during morpho-physiological development and food changes from rotifers to Artemia. All enzymatic activities were detected in rotifers and Artemia, and their contribution to enhancement the digestion capacity of the larvae appears to be low, but cannot be minimised. We concluded that the enzymatic equipment of P. maculatofasciatus larvae is similar to that of other marine fish species, that it becomes complete between days 12 and 18 after hatching, and that it is totally efficient up to 25 dah.
Abstract.— The effect on growth and survival of the initial stocking density (50, 100, 150, and 200 larvae/ L) in larval rearing of spotted sand bass was evaluated over 30 d in a closed recirculating system. Larvae were fed with rotifers, copepods, nauplii and adult Artemia, and spotted sand bass yolk‐sac larvae. Water quality was monitored daily. The notochordal or standard length of sampled larvae was measured by image analysis. Specific growth rates at each density were compared by covariance analysis. Survival was estimated from day 15 to the end of the experiment, when a resistance test was used to evaluate the juvenile quality among densities. At the end of the experiment, mean standard length of larvae at lower densities was significantly larger (P < 0.05) than at higher densities. Higher specific growth rates were found at lower densities. Significantly higher survival (P < 0.05) was recorded for the lowest density, but the highest number of harvested fish was obtained with the highest densities (150 and 200 larvae/L). The lowest density also showed the significantly (P < 0.05) higher survival after using a resistance test. We conclude the highest density can be used in larval rearing of spotted sand bass. However, better survival, growth, and seed quality are obtained at the lowest density. To recommend an optimal density for this specie, it is necessary to improve the water quality in the culture system and to make a cost‐benefit study.
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