The β-lactam antibiotics: past, present, and future

The discovery and development of the -lactam antibiotics are among the most powerful and successful achievements of modern science and technology. Since Fleming's accidental discovery of the penicillin-producing mold, seventy years of steady progress has followed, and today the -lactam group of compounds are the most successful example of natural product application and chemotherapy. Following on the heels of penicillin production by Penicillium chrysogenum came the discoveries of cephalosporin formation by Cephalosporium acremonium, cephamycin, clavam and carbapenem production by actinomycetes, and monocyclic -lactam production by actinomycetes and unicellular bacteria. Each one of these groups has yielded medically-useful products and has contributed to the reduction of pain and suffering of people throughout the world. Research on the microbiology, biochemistry, genetics and chemistry of these compounds have continued up to the present with major contributions being made by both individual and collaborative groups from industry and academia. The discovery of penicillin not only led to the era of the wonder drugs but provided the most important antibiotics available to medicine. Continued efforts have resulted in the improvement of these compounds with respect to potency, breadth of spectrum, activity against resistant pathogens, stability and pharmacokinetic properties. On the research front, major advances are being made on structural and regulatory biosynthetic genes and metabolic engineering of the pathways involved. New semisynthetic compounds especially those designed to combat resistance development are being examined in the clinic, and unusual non-antibiotic activities of these compounds are being pursued. Although seventy years of age, the -lactams are not yet ready for retirement.     

MHC class I genes of the channel catfish: sequence analysis and expression

 Four cDNAs encoding the major histocompatibility complex (MHC) class I α chain were isolated from a channel catfish clonal B-cell cDNA library. Sequence analysis suggests these cDNAs represent three different MHC class I loci. All cDNAs encoded conserved residues characteristic of the MHC class I α chain: namely, those involved in peptide binding, salt bridges, disulfide bond formation, and glycosylation. Southern blot analyses of individual outbred and second-generation gynogenetic fish indicated the existence of both polygenic and polymorphic loci. Northern blot studies demonstrated that catfish B, T, and macrophage cell lines transcribed markedly higher levels of class I α and β₂-microglobulin (β₂m) mRNA than fibroblast cell lines. In addition, immunoprecipitation data showed that a 41 000 M _r glycoprotein (presumably class I α) was associated with β₂m on the surface of catfish B cells. This latter finding is the first direct evidence for the cell surface association of β₂m with the MHC class I α chain on teleost cells and supports the notion that functional MHC class I proteins exist in teleosts. Received: 25 March 1998 / Revised: 28 July 1998     

Genetic transformation via particle bombardment of Catharanthus roseus plants through adventitious organogenesis of buds

In vitro propagation of Catharanthus roseus was achieved using nodal explants. Bud induction was best on medium containing 1.0 mg benzyl aminopurine l^–1. Hardening of rooted shoots to soil was very successful with 98% survival. Genetically transformed C. roseus plantlets were obtained after bombardment of nodal explants, which were then micropropagated, with DNA coated particles with green fluorescent protein (GFP) or -glucuronidase (GUS) reporter genes. Histological studies showed that the gene insertion method proved effective with many cells and different tissues displaying the reporter gene signals, showing that gene expressions were rather stable.     

Metabolic engineering of the terpenoid biosynthetic pathway of Escherichia coli for production of the carotenoids β-carotene and zeaxanthin

Metabolic engineering of the early non-mevalonate terpenoid pathway of Escherichia coli was carried out to increase the supply of prenyl pyrophosphates as precursor for carotenoid production. Transformation with the genes dxs for over-expression of 1-deoxy-d-xylulose 5-phosphate synthase, dxr for 1-deoxy-d-xylulose 5-phosphate reductoisomerase and idi encoding an isopentenyl pyrophosphate stimulated carotenogenesis up to 3.5-fold. Co-transformation of idi with either dxs or dxr had an additive effect on ß-carotene and zeaxanthin production which reached 1.6 mg g^–1 dry wt.     

Synthesis of alkyl fucosides through β-glucosidase-catalyzed condensation of fucose and 1-alcohols

-Glucosidase from almond catalyzed condensations of fucose and 1-alcohols with carbon numbers of 6 to 8 produce the corresponding 1-alkyl -d-fucosides. The enzyme also catalyzed the condensation of galactose and 1-hexanol. The conversion for the synthesis of hexyl fucoside was higher than those for the syntheses of hexyl glucoside and galactoside. The effect of initial saccharide concentrations on the conversions to alkyl glycosides was examined. The conversions at day 8 were almost the same at the low initial concentrations of the saccharides. However, the conversion significantly decreased as the concentrations increased. The surfactant properties of the prepared alkyl glycosides were measured. The critical micelle concentrations of the alkyl fucosides were lower than those of the glucosides and galactosides with the same alkyl chains.     

Production of a highly glucose-tolerant extracellular β-glucosidase by three Aspergillus strains

Quercetin was the best inducer for the production of a highly glucose-tolerant, extracellular -glucosidase in Aspergillus niger and Aspergillus oryzae. The enzyme was separated from the major and common -glucosidase by gel filtration and that from Aspergillus oryzae further purified by ion-exchange chromatography. It was highly resistant to glucose inhibition (Ki= 953 mM), had a pI of 4.2, optimum pH of 4.5–6.0 and a molecular mass of 30 kDa according to gel filtration. The enzyme was active against cellobiose and alkyl glucosides.     

Glycosylated α-chymotrypsin as a catalyst for kyotorphin synthesis in water-organic media

-Chymotrypsin was covalently modified with cellobiose by chemical means. After adsorption on to a porous polyamide support, both the native and the glycosylated immobilized derivatives were used to synthesize a kyotorphin derivative (N-benzoyl-l-tyrosyl-l-argininamide) in acetonitrile/water. Glycosylated chymotrypsin gave a 125% increase in product formation (750 nmol mg^–1 catalyst in 3 h) at 60% (v/v) acetonitrile/water. Maximal protective effect of this glycosylation process was at 70% (v/v) acetonitrile/water, at which concentration the half-life of the glycosylated enzyme was 20-times longer than that of the native form (52 min and 2.8 min, respectively).     

Quantification of extracellular α-acetolactate oxidative decarboxylation in diacetyl production by an α-acetolactate overproducing strain of Lactococcus lactis sp. lactis bv. diacetylactis

The quantification of -acetolactate (AAL) extracellular oxidative decarboxylation during an AAL overproducing strain culture shows that this reaction is at the origin of about 90% of the diacetyl production and that only a small proportion of extracellular AAL is readily transformed to diacetyl. These results, compared with previous ones obtained with a non AAL accumulating strain, allow research options to be put forward for the improvement of microbiological diacetyl production.