Biomedical subjects

N B Bhatnagar

Publications and source records attributed to N B Bhatnagar.

5 recordsLinked to original sources

PubMed2004

Bacterial insecticidal toxins.

Over the years it has been important for humans to control the populations of harmful insects and insecticides have been used for this purpose in agricultural and horticultural sectors. Synthetic insecticides, owing to their various side effects, have been widely replaced by biological insecticides. In this review we attempt to describe three bacterial species that are known to produce insecticidal toxins of tremendous biotechnological, agricultural, and economic importance. Bacillus thuringiensis (BT) accounts for 90% of the bioinsecticide market and it produces insecticidal toxins referred to as delta endotoxins. The other two bacteria belong to the genera Photorhabdus and Xenorhabdus, which are symbiotically associated with entomopathogenic nematodes of the families Heterorhabditidae and Steinernematidae respectively. Whereas, Xenorhabdus and Photorhabdus exist in a mutualistic association with the entomopathogenic nematodes, BT act alone. BT formulations are widely used in the field against insects; however, over the years there has been a gradual development of insect resistance against BT toxins. No resistance against Xenorhabdus or Photorhabdus has been reported to date. More recently BT transgenic crops have been prepared; however, there are growing concerns about the safety of these genetically modified crops. Nematodal formulations are also used in the field to curb harmful insect populations. Resistance development to entomopathogenic nematodes is unlikely due to the physical macroscopic nature of infection. Xenorhabdus and Photorhabdus transgenes have not yet been prepared; but are predicted to be available in the near future. In this review we start with an overview of the synthetic insecticides and then discuss Bacillus thuringiensis, Xenorhabdus nematophilus, and Photorhabdus luminescens in greater detail.

Agriculture↗

PubMed2001

The ptsH gene from Bacillus thuringiensis israelensis. Characterization of a new phosphorylation site on the protein HPr.

The ptsH gene from Bacillus thuringiensis israelensis (Bti), coding for the phosphocarrier protein HPr of the phosphotransferase system has been cloned and overexpressed in Escherichia coli. Comparison of its primary sequence with other HPr sequences revealed that the conserved His15 and Ser46 residues were shifted by one amino acid and located at positions 14 and 45, respectively. The biological activity of the protein was not affected by this change. When expressed in a Bacillus subtilis ptsH deletion strain, Bti HPr was able to complement the functions of HPr in sugar uptake and glucose catabolite repression of the gnt and iol operons. A modified form of HPr was detected in Bti cells, and also when Bti ptsH was expressed in E. coli or B. subtilis. This modification was identified as phosphorylation, because alkaline phosphatase treatment converted the modified form to unmodified HPr. The phosphoryl bond in the new form of in vivo phosphorylated HPr was resistant to alkali treatment but sensitive to acid treatment, suggesting phosphorylation at a histidine residue. Replacement of His14 with alanine in Bti HPr prevented formation of the new form of phosphorylated HPr. The phosphorylated HPr was stable at 60 degrees C, in contrast with HPr phosphorylated at the N delta 1 position of His14 with phosphoenolpyruvate and enzyme I. (31)P-NMR spectroscopy was used to show that the new form of P-HPr carried the phosphoryl group bound to the N epsilon 2 position of His14 of Bti HPr. Phosphorylation of HPr at the novel site did not occur when Bti HPr was expressed in an enzyme I-deficient B. subtilis strain. In addition, P-(N epsilon 2)His-HPr did not transfer its phosphoryl group to the purified glucose-specific enzyme IIA domain of B. subtilis.

Alkaline Phosphatase↗

PubMed1995

Heat stress alters the virulence of a rifampin-resistant mutant of Francisella tularensis LVS.

We have studied the stress response of a rifampin-resistant mutant of Francisella tularensis LVS. This mutant, Rif 7, was avirulent with an intraperitoneally administered 50% lethal dose greater than 10(7) CFU in a murine model of infection. Exposure of Rif 7 to heat stress for 5 h in vitro resulted in a 2-log decrease in its 50% lethal dose (P < 0.02). The increase in virulence was dependent on the time of exposure to high temperature and was maximal at 5 h. Envelope preparations from heat-stressed cells showed increased levels of several proteins. Notable among these were polypeptides with approximate molecular masses of 16, 60, and 75 kDa. Increases in both virulence and envelope protein levels were reversed when heat-treated cells were subsequently grown at 37 degrees C. Inhibition of protein synthesis by actinomycin D during heat stress blocked the increase in virulence of Rif 7. Cell-free media from the heat-stressed Rif 7 reacted with the whole spectrum of bacterial proteins were not toxic to mice. Hyperimmune serum against Rif 7 reacted with the whole spectrum of bacterial proteins in Western blots (immunoblots), although its reaction with 34- and 45-kDa proteins and two 60- and 75-kDa proteins upregulated during heat stress was weak. Other stress conditions, low iron and low pH, caused similar increases in the virulence of Rif 7. However, examination of the protein profile did not reveal any major common polypeptides induced by different stresses. Heat-treated Rif 7 bacteria were fully able to replicate in macrophages in vitro and in the host tissues, even though heat treatment only partially restored virulence.

Animals↗

PubMed1990

Molasses induced changes in Saccharomyces cerevisiae: alterations in plasma membrane structure and function and metallothionein level.

Growth of yeast cells in molasses caused changes in plasma membrane properties. The polypeptide profile of plasma membrane prepared by sucrose density gradient centrifugation showed a range of new polypeptides above 55 kD which were not present in malt extract-glucose-yeast extract-peptone medium grown cells. Isolated new bands appeared in the range of 25-50 kD. Transport of glucose was markedly enhanced in molasses trained cells. Among the amino acids, L-lysine uptake was decreased while L-aspartate uptake was enhanced considerably. Finally the metallothionein levels in the cells grown in molasses was found to be increased significantly, possibly to protect the cells from the harmful effect of heavy metal ions.

Alanine↗

PubMed1984

Characterization and metabolism of cyclic guanosine 3'5'-monophosphate in Mycobacterium smegmatis.

Cyclic guanosine 3'5'-monophosphate was isolated and purified from Mycobacterium smegmatis TMC 1515 using ion exchange chromatography. It was characterized by thin layer chromatography and radioimmunoassay. Guanylate cyclase and cGMP phosphodiesterase were detected in the cytosolic and particulate (37,000 X g pellet) fractions respectively. On the basis of our observations, cGMP appears to play a dual role (i) at the time of induction of cell proliferation and (ii) protects the bacteria against unfavourable surroundings during stationary phase of the growth. This is the first report demonstrating presence of cGMP, guanylate cyclase and cGMP phosphodiesterase in mycobacteria.

3',5'-Cyclic-GMP Phosphodiesterases↗