The metalloprotease gene of Serratia marcescens strain SM6

Summary Utilizing the DNA sequence of the metalloprotease fromSerratia strain E-15, we isolated and sequenced the homologous gene fromSerratia strain SM6. These two genes are similar at both the DNA and protein sequence level. Expression of the protease gene inEscherichia coli was achieved by use of thelac promoter. This resulted in the production and excretion of an immunologically detectable but inactive protein of slightly higher molecular weight than that fromSerratia. We introduced the cloned gene into previously described protease mutants. The observed pattern of protease expression suggested that these mutations fall into three classes.     

Decreased Enterobacteriaceae translocation due to gut microbiota remodeling mediates the alleviation of premature aging by a high-fat diet

Aging-associated microbial dysbiosis exacerbates various disorders and dysfunctions, and is a major contributor to morbidity and mortality in the elderly, but the underlying cause of this aging-related syndrome is confusing. SIRT6 knockout (SIRT6 KO) mice undergo premature aging and succumb to death by 4 weeks, and are therefore useful as a premature aging research model. Here, fecal microbiota transplantation from SIRT6 KO mice into wild-type (WT) mice phenocopies the gut dysbiosis and premature aging observed in SIRT6 KO mice. Conversely, an expanded lifespan was observed in SIRT6 KO mice when transplanted with microbiota from WT mice. Antibiotic cocktail treatment attenuated inflammation and cell senescence in KO mice, directly suggesting that gut dysbiosis contributes to the premature aging of SIRT6 KO mice. Increased Enterobacteriaceae translocation, driven by the overgrowth of Escherichia coli, is the likely mechanism for the premature aging effects of microbiome dysregulation, which could be reversed by a high-fat diet. Our results provide a mechanism for the causal link between gut dysbiosis and aging, and support a beneficial effect of a high-fat diet for correcting gut dysbiosis and alleviating premature aging. This study provides a rationale for the integration of microbiome-based high-fat diets into therapeutic interventions against aging-associated diseases.     

Dynamics of the normal gut microbiota: A longitudinal one-year population study in Sweden

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A kinetic study of NMC-A β-lactamase, an Ambler class A carbapenemase also hydrolyzing cephamycins

Abstract In order to analyze its kinetic parameters, an Ambler class A carbapenemase NMC-A was purified. NMC-A demonstrated unusually strong hydrolytic activity towards imipenem and meropenem. Moreover, it hydrolyzed cephamycins with k _cat values uncommonly high for this class of β-lactamases. Clavulanic acid and tazobactam had comparable inhibitory activity against NMC-A, whereas sulbactam was the least active inhibitor. Noticeably, NMC-A was more readily inhibited by brobactam. All these catalytic properties suggest that NMC-A possesses an original structure of its active site allowing hydrolysis of β-lactams usually stable to the hydrolytic activity of class A β-lactamases.     

Isolation of Enterobacter cowanii from Eucalyptus showing symptoms of bacterial blight and dieback in Uruguay

Aims:  This study was performed to identify bacterial strains isolated simultaneously with Pantoea species from Eucalyptus trees showing symptoms of bacterial blight and dieback in Uruguay.
Methods and Results:  Several molecular techniques including 16S rRNA and rpoB gene sequencing and DNA–DNA hybridization were used to characterize the Gram-negative, facultatively anaerobic, slime-producing bacterial strains isolated along with Pantoea species from Eucalyptus . Hypersensitivity reactions (HR) and pathogenicity tests were performed on tobacco and Eucalyptus seedlings, respectively. The isolates clustered closely with the type strain of Enterobacter cowanii in both phylogenetic trees constructed. The DNA–DNA similarity between the isolates and the type strain of Ent. cowanii ranged from 88% to 92%. A positive HR was observed on the tobacco seedlings, but no disease symptoms were visible on the inoculated Eucalyptus seedlings.
Conclusions:  Enterobacter cowanii was isolated from trees with symptoms of bacterial blight although strains of this bacterial species do not appear to be the causal agent of the disease.
Significance and Impact of the Study:  This study provides the first report of Ent. cowanii isolated from Eucalyptus . Its presence in Eucalyptus tissue suggests that it is an endophyte in trees showing symptoms of blight.     

Metabolism of L(−)-carnitine by Enterobacteriaceae under aerobic conditions

Different Enterobacteriaceae, such as Escherichia coli, Proteus vulgaris and Proteus mirabilis, are able to convert L(-)-carnitine, via crotonobetaine, into gamma-butyrobetaine in the presence of carbon and nitrogen sources under aerobic conditions. Intermediates of L(-)-carnitine metabolism (crotonobetaine, gamma-butyrobetaine) could be detected by thin-layer chromatography. In parallel, L(-)-carnitine dehydratase, carnitine racemasing system and crotonobetaine reductase activities were determined enzymatically. Monoclonal antibodies against purified CaiB and CaiA from E. coli O44K74 were used to screen cell-free extracts of different Enterobacteriaceae (E. coli ATCC 25922, P. vulgaris, P. mirabilis, Citrobacter freundii, Enterobacter cloacae and Klebsiella pneumoniae) grown under aerobic conditions in the presence of L(-)-carnitine.     

Control by cAMP-CRP complex of the expression of the PTS-dependent Erwinia chrysanthemi clb genes in Escherichia coli

Abstract Influence of the crp, cya and ptsIH gene products on the functioning and/or regulation of the Erwinia chrysanthemi clb genes was studied in Escherichia coli . Transport of cellobiose was found to be mediated by the phosphotransferase system and the expression of the clb genes to be positively controlled by the cAMP-CRP complex. We postulate that the same situation may occur in E. chrysanthemi .     

Enterobacteriaceae Taxonomy Approached by Minimization of Stochastic Complexity

We discuss the taxonomy of Enterobacteriaceae in the light of classification by minimization of stochastic complexity (SC). A classification which minimizes SC is optimal from the point of view of information theory. It was found that the SC-minimizing classification of a large database of strains of Enterobacteriaceae resulted in structures which correspond well to the conclusions of experts on the taxonomy of Enterobacteriaceae. The approach based on minimization of SC can therefore be considered as useful in bacterial taxonomy.