When grown anaerobically on L-rhamnose, Salmonella typhimurium excreted 1,2-propanediol as a fermentation product. Upon exhaustion of the methyl pentose, 1,2-propanediol was recaptured and further metabolized, provided the culture was kept under anaerobic conditions. n-Propanol and propionate were found in the medium as end products of this process at concentrations one-half that of 1,2-propanediol. As in Klebsiella pneumoniae (T. Toraya, S. Honda, and S. Fukui, J. Bacteriol. 139:3947, 1979), a diol dehydratase which transforms 1,2-propanediol to propionaldehyde and the enzymes involved in a dismutation that converts propionaldehyde to n-propanol and propionate were induced in S. typhimurium cultures able to transform 1,2-propanediol anaerobically.In Escherichia coli, L-rhamnose is metabolized by the sequential action of a rhamnose permease that transports the sugar across the membrane, a rhamnose isomerase (20) that converts it to L-rhamnulose, a rhamnulose kinase (21) that phosphorylates the L-rhamnulose to L-rhamnulose 1-phosphate, and an aldolase (5) that cleaves the L-rhamnulose 1-phosphate into dihydroxyacetone phosphate and L-lactaldehyde. Although no detailed description of the enzymes has been reported, the same pathway has been described in Salmonella typhosa (7) and Salmonella typhimurium (1).Under anaerobic conditions, E. coli induces an NADHdependent oxidoreductase that reduces L-lactaldehyde to 1,2-propanediol, which is excreted into the medium (4). On the basis of propanediol oxidoreductase activity induction and propanediol excretion, this fermentation mechanism has also been proposed for S. typhimurium (3). However, 1,2-propanediol, which is not further metabolized in anaerobic E. coli cultures, gradually disappears from the medium in S. typhimurium cultures maintained under similar anaerobic conditions (J. Badia, unpublished observation).Aerobic metabolism of 1,2-propanediol has been described for several species (9, 13) and for mutant cells of E. coli (18) able to grow on the diol. In all cases the first step is the oxidation to lactaldehyde through the action of an oxidoreductase. Lactaldehyde is subsequently metabolized to lactate and pyruvate (6,17). In contrast, anaerobic metabolism of 1,2-propanediol in Klebsiella pneumoniae (22) or Clostridium glycolicum (8) has been reported to be mediated by a coenzyme B12-dependent diol dehydratase that yields propionaldehyde, which is immediately metabolized by a dismutation to n-propanol and propionate.In this report we characterize the 1,2-propanediol transformation that occurs in S. typhimurium cultures and establish the metabolic pathway involved.

Growth experiments with Escherichia coli have shown that this organism is able to use allantoin as a sole nitrogen source but not as a sole carbon source. Nitrogen assimilation from this compound was possible only under anaerobic conditions, in which all the enzyme activities involved in allantoin metabolism were detected. Of the nine genes encoding proteins required for allantoin degradation, only the one encoding glyoxylate carboligase (gcl), the first enzyme of the pathway leading to glycerate, had been identified and mapped at centisome 12 on the chromosome map. Phenotypic complementation of mutations in the other two genes of the glycerate pathway, encoding tartronic semialdehyde reductase (glxR) and glycerate kinase (glxK), allowed us to clone and map them closely linked to gcl. Complete sequencing of a 15.8-kb fragment encompassing these genes defined a regulon with 12 open reading frames (ORFs). Due to the high similarity of the products of two of these ORFs with yeast allantoinase and yeast allantoate amidohydrolase, a systematic analysis of the gene cluster was undertaken to identify genes involved in allantoin utilization. A BLASTP search predicted four of the genes that we sequenced to encode allantoinase (allB), allantoate amidohydrolase (allC), ureidoglycolate hydrolase (allA), and ureidoglycolate dehydrogenase (allD). The products of these genes were overexpressed and shown to have the predicted corresponding enzyme activities. Transcriptional fusions to lacZpermitted the identification of three functional promoters corresponding to three transcriptional units for the structural genes and another promoter for the regulatory gene allR. Deletion of this regulatory gene led to constitutive expression of the regulon, indicating a negatively acting function.

Transcriptional regulation of the rhaT gene, one of the operons forming the rhamnose regulon in Escherichia coli, was studied by fusing its complete or deleted promoter to the reporter gene lacZ. Analysis of p-galactosidase activities induced in these constructions grown under different conditions predicted the presence of two putative control elements: one for the RhaS regulatory protein and activating the gene not only by L-rhamnose but also by L-lyxose or L-mannose, the other for CAMP-catabolite repression protein and activating this gene in the absence of glucose. Anaerobiosis increased the promoter function two-to threefold with respect to the aerobic condition. Experiments involving complementation of strains containing the rhaTpromoter fusion and carrying a deletion in the rhaS and/or rhaR genes with plasmids bearing the rhamnose regulatory genes showed that rhaT is controlled by a regulatory cascade, in which RhaR induces rhaSR and the accumulated RhaS directly activates rhaT.

The genes encoding the enzymes in the D-glucarate and D-galactarate pathways have been identified in the Escherichia coli genome and found to be distributed in apparently three transcriptional units ( Fig. 1) (1), and tartronate semialdehyde reductase (9) showed that both enzyme systems were induced by growth on either of the carbon sources. D-Glycerate was the best inducer (Table 1).Expression of the transcriptional units. To identify the functional promoters in the D-galactarate and D-glucarate systems, different fragments of the two gene clusters were fused to the lacZ gene of plasmid pRS550 or pRS551 (17) and introduced as a single copy in the genomic background of MC4100 as described by Elliott (10). Analysis of the ␤-galactosidase activities (14) showed the presence of promoter function only 5Ј of the following genes: yhaG (proposed name, garD), yhaU (proposed name, garP), and b2789 (proposed name, gudP) (Fig. 1). A garP::Tn5 insertion mutant (strain JA175) was obtained from strain MC4100 as described by Bruijn and Lupski (7). Impairment of D-glucarate and D-glycerate utilization in this mutant, which lacks the function of downstream genes in the garPLRK operon due to polarity effects, also indicated that no other promoter activity lies in this operon.␤-Galactosidase activities of ⌽(garD-lacZ), ⌽(garP-lacZ), and ⌽(gudP-lacZ) were found to be induced in cultures grown in the presence of D-galactarate, D-glucarate, or D-glycerate compared to the basal levels obtained in glycerol. The activation was two-to threefold higher in D-glycerate than in Dgalactarate or D-glucarate (Fig. 2). These results indicated a coordinate regulation of these three promoters. No induction was observed with other related sugars, such as D-glucuronic acid or D-galacturonic acid. The inducing capacity of any of the three compounds observed in strain JA175, which was unable to form D-glycerate from D-galactarate or D-glucarate, indicated that all of them acted as inducers. Induction by D-galactarate in strain JA175, which lacks galactarate permease, showed that this substrate is able to enter the cells by another permease, probably D-glucarate permease. This finding would be supported by the high similarity displayed by these two permeases (12). These results led us to explore if the three promoters were under the control of a common regulatory protein recognizing any of the three substrates as an inducer.Isolation and mapping of pleiotropic mutants. To search for a common regulator, 10 4 cells of strain MC4100 bearing ⌽(garD-lacZ) were mutated by ethyl methanesulfonate (14) and screened for blue and white colonies on glycerol plates containing D-glucarate and 5-bromo-4-chloro-3-indolyl-␤-Dgalactoside. From among the white colonies we selected those that were unable to grow on D-glucarate, D-galactarate, or D-glycerate but able to grow on other carbon sources. These cells displayed no ␤-galactosidase activity and no detectable galactarate or glucarate dehydratase, tartronate semialdehyde reductase, or glycerate kinase activities wh...

Oleic acid has been reported as a good inducer of lipase production by Candida rugosa. In order to know if this enzyme is induced by oleic acid itself or by a metabolite, different short chain fatty acids were tested. Butyric acid was the best carbon source to growth microorganism but it did not induce lipase production. Although caprylic and capric acid were the best inducers of lipase production, at concentrations up 1 g/1 they have toxic effect in Candida rugosa growth. Thus, from the point of view of industrial production oleic acid could be considered as the best substrate tested.