Giant catfish Pangasianodon gigas growth hormone-encoding cDNA: cloning and sequencing by one-sided polymerase chain reaction

cDNA clones encoding giant catfish (Pangasianodon gigas) growth hormone (GH) have been isolated using a polymerase chain reaction (PCR) strategy. Pairwise combinations of degenerate and general primers allowed for the amplification of regions both 3' and 5' to the point of entry into the message. The amplified PCR products were cloned and sequenced. The cDNA sequence was found to encode a polypeptide of 200 amino acids (aa), including a putative signal peptide of 22 aa. The 5' and 3' untranslated regions of the message are 58 and 515 nucleotides long, respectively. The giant catfish GH displays the highest aa sequence homology with the carp GH, with 80% of sequence identity. Moreover, giant catfish GH has structural features in common with both mammalian and avian GH polypeptides, and also contains the domains of conserved sequence found in other GH.     

Expression of the catalase gene katA in starter culture Lactobacillus plantarum TISTR850 tolerates oxidative stress and reduces lipid oxidation in fermented meat product

The catalase gene katA of Lactobacillus sakei SR911 was cloned and expressed in Escherichia coli UM2 and Lactobacillus plantarum TISTR850 under strong lactococcal promoter P59 in E. coli-lactococcus expression vector pIL1020. The L. plantarum TISTR850 is a catalase-deficient strain isolated from local fermented meat product. The recombinant L. plantarum TISTR850 was shown to decompose hydrogen peroxide, and catalase activity approximately three times higher that of natural catalase-producing strain L. sakei SR911. The recombinant protein was also detected by in situ activity staining of the catalase enzyme. The recombinant L. plantarum TISTR850 did not accumulate hydrogen peroxide under glucose-limited aerobic conditions and remained viable after 60 h of incubation. The recombinant and host strain L. plantarum TISTR850 were used as starter cultures in the fermented meat product, and lipid oxidation was monitored over a 7-day storage at 20 degrees C determined as thiobarbituric acid-reactive substances (TBARS) value. The lipid oxidation level in the fermented meat product seeded with the catalase genetically modified starter culture L. plantarum TISTR850 was significantly lower than that of the natural catalase-deficient strain.     

A simple, rapid and sensitive detection of salmonella in food by polymerase chain reaction

A polymerase chain reaction (PCR) method was developed for detection of salmonella in food. A set of PCR primers was designed to amplify a 199 bp salmonella-specific DNA fragment derived from a repetitive DNA of Salmonella Weltevreden. The assay detected all 52 most prevalent serovars found in contaminated food in Thailand and no cross-reaction was observed with other non-salmonella organisms. The limit of detection was 1 fg of purified target DNA or five bacteria from pure culture. The detection of artificially contaminated food performed following a 6 h enrichment step was three bacteria per gram and the result was obtained within 4 h.     

Isolation of nisin-producing Lactococcus lactis WNC 20 strain from nham,a traditional Thai fermented sausage

A total of 14,020 lactic acid bacteria (LAB) were isolated from nham and screened for bacteriocin production. One Lactococcus lactis strain WNC 20 produced a bacteriocin that not only inhibited closely related LAB, but also some food-borne pathogens including Listeria monocytogenes, Clostridium perfringens, Bacillus cereus and Staphylococcus aureus. Biochemical studies revealed that the bacteriocin was heat-stable even at autoclaving temperature (121 degrees C for 15 min) and was active over a wide pH range (2-10). The bacteriocin was inactivated by alpha-chymotrypsin and proteinase K but not other proteases. The antimicrobial spectrum and some characteristics of this bacteriocin were nearly identical to that of nisin. The gene encoding this bacteriocin was amplified by polymerase chain reaction (PCR) with nisin gene-specific primer. Sequencing of this gene showed identical sequences to nisin Z as indicated by the substitution of asparagine residue instead of histidine at position 27. The ability of the bacteriocin produced by Lc. lactis WNC 20 may be useful in improving the food safety of the fermented product.     

A Hybrid Key Predistribution Scheme for Sensor Networks Employing Spatial Retreats to Cope with Jamming Attacks

In order to provide security services in wireless sensor networks, a well-known task is to provide cryptographic keys to sensor nodes prior to deployment. It is difficult to assign secret keys for all pairs of sensor node when the number of nodes is large due to the large numbers of keys required and limited memory resources of sensor nodes. One possible solution is to randomly assign a few keys to sensor nodes and have nodes be able to connect to each other with some probability. This scheme has limitations in terms of the tradeoffs between connectivity and memory requirements. Recently, sensor deployment knowledge has been used to improve the level of connectivity while using lesser amounts of memory space. However, deployment based key predistribution schemes may cause a large number of nodes to be cryptographically isolated if nodes move after key pre-distribution. Mobility may be necessitated for reasons depending on applications or scenarios. In this paper, we consider mobility due to spatial retreat of nodes under jamming attacks as an example. Jamming attacks are easy and efficient means for disruption of the connectivity of sensors and thus the operation of a sensor network. One solution for mobile sensor nodes to overcome the impact of jamming is to perform spatial retreats by moving nodes away from jammed regions. Moved nodes may not be able to reconnect to the network because they do not have any shared secret with new neighbors at new locations if strict deployment knowledge based key predistribution is employed. In this paper, we propose a hybrid key predistribution scheme that supports spatial retreat strategies to cope with jamming attacks. Our scheme combines the properties of random and deployment knowledge based key predistribution schemes. In the presence of jamming attacks, our scheme provides high key connectivity (similar to deployment knowledge based schemes) while reducing the number of isolated nodes. We evaluate the performance of our scheme through simulations and analysis.     

Isolation of bacterial strains colonizable in mosquito larval guts as novel host cells for mosquito control

We screened for microorganisms that can be utilized as new host cells for mosquito larvicides. As long persistence in the environment is required of host cells, we examined the bacterial populations in the guts of mosquito larvae collected from natural breeding habitats. Larvae of Aedes aegypti and Culex quinquefasciatus were examined, and Bacillus species, particularly Bacillus cereus, were found to be the dominant bacterial species in their guts. To investigate the relationship between these Bacillus strains and the mosquito larvae, we re-introduced the bacteria into larvae of Aedes aegypti, C. quinquefasciatus and another common mosquito strain, Anopheles dirus. The cell numbers of Bacillus cereus strains Ae10 and Cx5 in the guts were consistent throughout a 7-d period without food supplementation, suggesting that these strains were able to colonize in the guts of the larvae. To confirm this, we introduced a plasmid containing a kanamycin resistance marker into Ae10 and Cx5 and fed these recombinant strains to C. quinquefasciatus larvae. Even when food was supplemented for 7 d, the recombinant strains, particularly Ae10, were still found in the guts. Under similar conditions, B. thuringiensis serovar israelensis c4Q2-72 was hardly detectable after 2 d, while Escherichia coli could not be detected at all. Their stable retention in mosquito larvae guts and the feasibility of genetic manipulation indicates these strains possess high potential as novel host cells for application in mosquito control.