Semisynthetic modifications of hemiaminal function at ornithine unit of mulundocandin, towards chemical stability and antifungal activity.

Mulundocandin (1), is an echinocandin class of lipopeptide. It has wide spectrum of antifungal activity against Candida and Aspergillus species. Semisynthetic modification at Ornithine-5-hydroxyl (hemiaminal function) of 1 was carried out to improve solution stability and hence in vivo activity. Synthesis of ether (C-OR), thioether (C-SR) and C-N linkage at hemiaminal function have been described. All synthetic analogues were evaluated for their stability in aqueous solution and found to be more stable than mulundocandin. Antifungal activity of Orn-5 analogues was evaluated both in vitro against Candida albicans and Aspergillus fumigatus by agar well method and in vivo (oral and intraperitoneal) in C. albicans infected Swiss mice. Results of in vivo assays of analogues 2-9 by the oral route suggests that the introduction of either oxygen nucleophiles (-OR) or sulphur nucleophiles (-SR), at either Orn-5 or at both Orn-5 and HTyr-4 positions, results in retaining the activity of the parent compound with improved aqueous stability in most cases. Compound 9 has shown improved antifungal activity in comparison to mulundocandin by oral application in Swiss mice.

Comparative chemotherapeutic efficacy of balhimycin, desgluco-balhimycin against experimental MSSA and MRSA infection in mice.

Balhimycin and desglucobalhimycin are glycopeptide antibiotics isolated from an Amycolatopsis spp during the search for novel antibacterials against MRSA from the natural product screening at the Research Centre of formerly Hoechst India Ltd. in Bombay, India. Both compounds show excellent in vitro activity against methicillin sensitive and resistant Staphylococcus aureus (MSSA, MRSA). Both compounds were also found to be active against a number of MRSA strain in the animal studies. The activities were comparable to that of the reference glycopeptides vancomycin and teicoplanin used in these studies. Teicoplanin displayed better in vivo efficacy against S. epidermidis 4929H and Streptococcus pyogenes A77 than either vancomycin or desgluco-balhimycin in the present study. Preliminary studies on pharmacokinetic and acute toxicity were done to get some idea at the early stage of the investigation about the promise of the compounds for development.

Antiamoebic activity of 3,3'-fluro-4,4'-di-(pyrrolidine-2-ylidene amino)-diphenyl (liroldine), against experimentally infected intestinal and hepatic amoebiasis.

HL 707, Liroldine, a novel synthetic compound, was found effective against both extraintestinal and intestinal amoebiasis in animal models. Its activity against hepatic infection in golden hamsters is comparable with that of different derivatives of nitroimidazoles used for human treatment. Against intestinal amoebiasis in Wistar rats, the activity was superior to nitroimidazoles and chloroquine. Paramomycin was comparable and diloxanide furoate was marginally superior. The comparative in vitro and in vivo studies with standard marketed drugs and Liroldine indicate an excellent profile of the compound against experimental amoebiasis. LD50 of Liroldine determined in mice is 910 mg/kg x 1, po and 940 mg/kg x 1 ip).

Comparative pathogenicity of trichomonas vaginalis isolated from symptomatic & asymptomatic cases.

Pathogenicity of 19 isolates of T.vaginalis obtained from vaginal specimens were studied in the murine model by intraperitoneal route. Sixteen isolates were recovered from the females with various clinical conditions and 3 isolates were from normal healthy females. Pathogenicity level of these isolates were studied by inoculating 5 mice per isolates through intraperitoneal route and the animals were sacrificed on tenth day post-inoculation. In general, all the isolates recovered produced infection in mice. On comparison with the reference strain obtained from Hoechst India Ltd., seven isolates recovered from symptomatic cases and one strain from healthy females produced severe infection in mice. Though variation in pathogenicity level was observed among the isolates, a definite correlation between clinical picture in natural host and pathogenicity in mice was not observed.

Antimalarial activity of novel ring-contracted artemisinin derivatives.

Bromoacetal 2 undergoes a novel ring-contracted reaction to give the aldehyde 3 in the presence of DBU or triethylamine. The aldehyde 3 is reduced to the alcohol 4 and oxidized to the carboxylic acid 5. The alcohol 4 reacts with dihydroartemisinin to give the two diastereoisomers 38 and 39. All the compounds were tested for antimalarial activity in mice infected with chloroquine sensitive Plasmodium berghei. If the activity of a compound was comparable to that of the standard compound, such as arteether, it was tested against chloroquine resistant NS strain infection in mice. Initially the compounds were administered subcutaneously, and if found to be active, they were tested by oral route. The antimalarial activity of compounds 19, 38, and 39 was found to be comparable to that of arteether when tested in K-173-infected mice. They were also active against chloroquine resistant NS strain infection in mice.

Comparative pathogenicity of Trichomonas vaginalis isolated from symptomatic and asymptomatic cases.

Pathogenicity of 19 isolates of Trichomonas vaginalis obtained from vaginal specimens were studied in the murine model by intraperitoneal inoculation. Sixteen isolates were recovered from the females with various clinical conditions and 3 isolates were from normal healthy females. Pathogenicity level of these isolates were studied by inoculating 5 mice per isolate through intraperitoneal route and the animals were sacrificed on the 10th day post-inoculation. In general, all the isolates recovered produced infection in mice. On comparison with the reference strain obtained from Hoechst India Ltd., seven isolates recovered from symptomatic cases and one strain from healthy females produced severe infection in mice. Though variation in the pathogenicity level was observed among the isolates, a definite correlation between the clinical picture in the natural host and pathogenicity in mice was not observed.

Cloning and characterization of genes for the PvuI restriction and modification system.

The genes encoding the endonuclease and the methylase of the PvuI restriction and modification system were cloned in E.coli and characterized. The genes were adjacent in tandem orientation spanning a distance of 2200 bases. The PvuI endonuclease was a single polypeptide with a calculated molecular weight of 27,950 daltons. The endonuclease was easily detectable when the gene was expressed from its endogenous promotor and present on a low copy plasmid, but expression was considerably enhanced when the endonuclease gene was placed under the control of a strong promoter on a high copy plasmid. The methylase did not completely protect plasmid DNA from R.PvuI digestion until the methylase gene was placed under lac promotor control in a multicopy plasmid. In the absence of the M.PvuI methylase, expression of the R.PvuI endonuclease from the lac promotor on a multicopy plasmid was not lethal to wild type E.coli, but was lethal in a temperature-sensitive ligase mutant at the non-permissive temperature. Moreover, induction of the R.PvuI endonuclease under lambda pL promotor control resulted in complete digestion of the E.coli chromosome by R.PvuI.

Mersacidin, a new antibiotic from Bacillus. In vitro and in vivo antibacterial activity.

Mersacidin is a new peptide antibiotic of the proposed lantibiotic family. It is active in vitro and in vivo against Gram-positive bacteria including the methicillin-resistant Staphylococci. Its in vitro activity is less than those of vancomycin and erythromycin but it shows much higher activity in the in vivo system than can be expected from the in vitro testing results. A water soluble potassium salt has been prepared which has an activity profile similar to that of mersacidin, but has better in vivo activity against Streptococcus pyogenes than the parent compound.

Genetic organization of the KpnI restriction--modification system.

The KpnI restriction-modification (KpnI RM) system was previously cloned and expressed in E. coli. The nucleotide sequences of the KpnI endonuclease (R.KpnI) and methylase (M. KpnI) genes have now been determined. The sequence of the amino acid residues predicted from the endonuclease gene DNA sequence and the sequence of the first 12 NH2-terminal amino acids determined from the purified endonuclease protein were identical. The kpnIR gene specifies a protein of 218 amino acids (MW: 25,115), while the kpnIM gene codes for a protein of 417 amino acids (MW: 47,582). The two genes transcribe divergently with a intergeneic region of 167 nucleotides containing the putative promoter regions for both genes. No protein sequence similarity was detected between R.KpnI and M.KpnI. Comparison of the amino acid sequence of M.KpnI with sequences of various methylases revealed a significant homology to N6-adenine methylases, a partial homology to N4-cytosine methylases, and no homology to C5-methylases.

Cloning and overexpression of the gene encoding bacteriophage T5 DNA polymerase.

T5 DNA polymerase (T5Pol), an essential enzyme for bacteriophage T5 DNA replication, is unusual because of its high processivity and strand-displacing ability. These two properties in a single polypeptide make T5Pol an ideal candidate for structural and functional analysis. Therefore, the structural gene encoding the DNA polymerase of bacteriophage T5 (T5pol) has been cloned and overexpressed in Escherichia coli. Elimination of sequences upstream from the 5' end of the T5pol by exonuclease III digestion was necessary to obtain stable clones containing a full-length structural gene. Determination of the nucleotide (nt) sequence of the region deleted during clone construction revealed the presence of a promoter sequence having extensive homology with known T5 phage 'early' promoters. By primer extension of mRNA isolated from T5 phage-infected cells, two successive G residues located 6 and 7 nt downstream from the -10 region of this promoter were identified as the initiating nt at the 5' end of T5pol mRNA. T5Pol produced in E. coli from the cloned gene under control of a tac or phage lambda pL promoter represented as much as 40% of total cell protein. The majority of the T5Pol present in extracts of E. coli was insoluble. The amount of active enzyme present was estimated to be a maximum of tenfold higher than that found in extracts of T5 phage-infected cells.

Cloning the KpnI restriction-modification system in Escherichia coli.

The genes encoding the KpnI restriction and modification (R-M) system from Klebsiella pneumoniae, recognizing the sequence, 5'-GGTAC decreases C-3', were cloned and expressed in Escherichia coli. Although the restriction endonuclease (ENase)- and methyltransferase (MTase)-encoding genes were closely linked, initial attempts to clone both genes as a single DNA fragment in a plasmid vector resulted in deletions spanning all or part of the gene coding for the ENase. Initial protection of the E. coli host with MTase expressed on a plasmid was required to stabilize a compatible plasmid carrying both the ENase- and the MTase-encoding genes on a single DNA fragment. However, once established, the MTase activity can be supplied in cis to the kpnIR gene, without an extra copy of kpnIM. A chromosomal map was generated localizing the kpnIR and kpnIM genes on 1.7-kb and 3.5-kb fragments, respectively. A final E. coli strain was constructed, AH29, which contained two compatible plasmids: an inducible plasmid carrying the kpnIR gene which amplifies copy number at elevated temperatures and a pBR322 derivative expressing M.KpnI. This strain produces approx. 10 million units of R.KpnI/g of wet-weight cells, which is several 1000-fold higher than the level of R.KpnI produced by K. pneumoniae. In addition, DNA methylated with M.KpnI in vivo does not appear to be restricted by the mcrA, mcrB or mrr systems of E. coli.

Enrichment for 5'-TG termini: a method for subcloning structural genes into expression vectors.

We describe a method for creating a population of randomly digested, blunt-ended DNA fragments with 5'-TG... 3'-AC... (TG) at their termini. When these fragments were ligated to a blunt-ended vector that contains ...CATA-3' ...GTAT-5' at its termini, as high as 84% of the clones obtained after transformation contained plasmids with a reconstructed Nde I site ... CATATG... ...GTATAC.... When the DNA vector is prepared from an appropriate plasmid [Gross et al., Mol. Cell. Biol. 5 (1985) 1015-1024; Kotewicz et al., Gene 35 (1985) 249-258], the ATG within the restriction site corresponds to a start codon positioned downstream from a strong ribosome-binding site and controllable promoter. If a gene has been digested to the TG contained within its authentic initiation codon, the endogenous translation-initiation control sequences are deleted and expression can be controlled using the plasmid-derived promoter. In addition, a gene digested to other in-frame TGs can potentially express proteins with altered N termini. Using this method, we have placed the structural gene of SP6 RNA polymerase, trimmed precisely to its authentic start codon, under the control of the tac promoter.

Expression of degradative genes of Pseudomonas putida in Caulobacter crescentus.

The recombinant plasmid RP4-TOL was transferred into Caulobacter crescentus at a high frequency, and the plasmid was maintained for at least 50 generations. C. crescentus cells which contained RP4-TOL grew on all the aromatic compounds that the plasmid normally allowed Pseudomonas putida to grow on. Reciprocal transfers from C. crescentus donor to P. putida or Escherichia coli recipients were less efficient and occurred at frequencies of approximately 10(-3). Some representative TOL-specified enzymes in cell-free extracts of C. crescentus(RP4-TOL) were inducible, and their levels were similar to those of P. putida. The amounts of mRNA from induced cells of C. crescentus(RP4-TOL) and P. putida(RP4-TOL) were also similar. Moreover, the restriction enzyme digestion maps of RP4-TOL from both C. crescentus and P. putida were the same, indicating that the expression of the TOL genes occurred without any apparent alteration of the gene structure. This suggest that the degradative genes of Pseudomonas spp. can be transferred, maintained, and expressed efficiently in C. crescentus and that the mechanism of transcriptional activation of TOL genes observed in C. crescentus is similar to that of Pseudomonas spp.

Metabolism of aromatic compounds by Caulobacter crescentus.

Cultures of Caulobacter crescentus were found to grow on a variety of aromatic compounds. Degradation of benzoate, p-hydroxybenzoate, and phenol was found to occur via beta-ketoadipate. The induction of degradative enzymes such as benzoate 1,2-dioxygenase, the ring cleavage enzyme catechol 1,2-dioxygenase, and cis, cis-muconate lactonizing enzyme appeared similar to the control mechanism present in Pseudomonas spp. Both benzoate 1,2-dioxygenase and catechol 1,2-dioxygenase had stringent specificities, as revealed by their action toward substituted benzoates and substituted catechols, respectively.

Nucleotide sequence and expression of clcD, a plasmid-borne dienelactone hydrolase gene from Pseudomonas sp. strain B13.

The clcD structural gene encodes dienelactone hydrolase (EC 3.1.1.45), an enzyme that catalyzes the conversion of dienelactones to maleylacetate. The gene is part of the clc gene cluster involved in the utilization of chlorocatechol and is carried on a 4.3-kilobase-pair BglII fragment subcloned from the Pseudomonas degradative plasmid pAC27. A 1.9-kilobase-pair PstI-EcoRI segment subcloned from the BglII fragment was shown to carry the clcD gene, which was expressed inducibly under the tac promoter at levels similar to those found in 3-chlorobenzoate-grown Pseudomonas cells carrying the plasmid pAC27. In this study, we present the complete nucleotide sequence of the clcD gene and the amino acid sequence of dienelactone hydrolase deduced from the DNA sequence. The NH2-terminal amino acid sequence encoded by the clcD gene from plasmid pAC27 corresponds to a 33-residue sequence established for dienelactone hydrolase encoded by the Pseudomonas sp. strain B13 plasmid pWR1. A possible relationship between the clcD gene and pcaD, a Pseudomonas putida chromosomal gene encoding enol-lactone hydrolase (EC 3.1.1.24) is suggested by the fact that the gene products contain an apparently conserved pentapeptide neighboring a cysteinyl side chain that presumably lies at or near the active sites; the cysteinyl residue occupies position 60 in the predicted amino acid sequence of dienelactone hydrolase.

Antiamoebic activity of chonemorphine, a steroidal alkaloid, in experimental models.

Chonemorphine, a steroidal alkaloid isolated from Chonemorpha fragrans Moon (Apocyanaceae) was identified as an antimoebic principle during the course of a screening programme for novel antiparasitic agents from plant sources. At a dosage of 100 mg/kg x 4 chonemorphine led to a 100% cure of experimental hepatic infection in golden hamsters and cleared 90% of the intestinal infection in weanling Wistar rats at 200 mg/kg (x4) dosages. The discovery of chonemorphine as an antiamoebic agent is an addition to the few known plant amoebicides such as emetine and conessine.

A set of cassettes and improved vectors for genetic and biochemical characterization of Pseudomonas genes.

A set of broad-host-range vectors allowing direct selection of recombinant DNA molecules to facilitate subcloning and expression analyses of Pseudomonas genes was constructed using Bg/II lacZ alpha cassette. Controlled expression vectors pVDtac39 and pVDtac24 were shown to be useful for determination of enzymatic activities encoded by the cloned DNA fragments and Mr determination of the corresponding polypeptides. A set of Pseudomonas putida xylE gene cassettes truncated at the 5' end was constructed for translational (protein) fusion studies. A protein fusion of the Pseudomonas aeruginosa algD gene, coding for GDPmannose dehydrogenase, and the truncated xylE gene cassette was used to verify the putative coding region and translational signals predicted from the algD nucleotide sequence.

Microbial degradation of halogenated compounds.

The mode of degradation of various halogenated compounds in isolated pure cultures and the disposition of the degradative genes have been studied. In many cases the degradative genes are found to be clustered on plasmids and appear to be under positive control. Genetic selection in vivo and genetic manipulations in vitro have allowed construction of strains having wider biodegradative potentials than their natural counterparts. Molecular cloning of the degradative gene clusters for halogenated compounds in vectors with a broad host range also allows the transfer of such genes to a large number of Gram-negative bacteria. The application of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)-degrading microorganisms has demonstrated the effectiveness of this strain in removing large amounts of 2,4,5-T from contaminated soil within a short period, and such soil has been shown to support the growth of plants normally sensitive to low concentrations of 2,4,5-T. The two major challenges that must be addressed in the near future are the development of appropriate microbial technology for the decontamination of soil containing hazardous halogenated compounds, and the promulgation of appropriate regulations to ensure the safety and well-being of the public during the application of genetically improved strains in an open environment.