We found that transcription of the pdxA and pdxB genes, which mediate steps in the biosynthesis of the essential coenzyme pyridoxal 5-phosphate, and the ksgA gene, which encodes an rRNA modification enzyme and is partly cotranscribed with pdxA, is subject to positive growth rate regulation in Escherichia coli K-12. The amounts of the pdxA-ksgA cotranscript and pdxB-and ksgA-specific transcripts and expression from pdxA-and pdxB-lacZ fusions increased as the growth rate increased. The half-lives of ksgA-and pdxB-specific transcripts were not affected by the growth rate, whereas the half-life of the pdxA-ksgA cotranscript was too short to be measured accurately. A method of normalization was applied to determine the amount of mRNA synthesized per gene and the rate of protein accumulation per gene. Normalization removed an apparent anomaly at fast growth rates and demonstrated that positive regulation of pdxB occurs at the level of transcription initiation over the whole range of growth rates tested. RNA polymerase limitation and autoregulation could not account for the positive growth rate regulation of pdxA, pdxB, and ksgA transcription. On the other hand, growth rate regulation of the amount of the pdxA-ksgA cotranscript was abolished by a fis mutation, suggesting a role for the Fis protein. In contrast, the fis mutation had no effect on pdxB-or ksgA-specific transcript amounts. The amounts of the pdxA-ksgA cotranscript and ksgA-specific transcript were repressed in the presence of high intracellular concentrations of guanosine tetraphosphate; however, this effect was independent of relA function for the pdxA-ksgA cotranscript. Amounts of the pdxB-specific transcript remained unchanged during amino acid starvation in wild-type and relA mutant strains.

Molecular studies of copper and cadmium resistances in acidophilic bacteria are significant in biomining. In this study, afe_1862, which encodes a heavy metal-binding protein in Acidithiobacillus ferrooxidans L1, was amplified using PCR, cloned into the pET32a plasmid, and sequenced. Following SDS-PAGE analysis, optimization of the expression conditions and heterologous overexpression of afe_1862 in Escherichia coli BL21 in the presence of Cu and Cd were studied as well. The results indicated that AFE_1862 has higher resistance to Cu than Cd. Bioinformatics analysis illustrated that AFE_1862 has a conserved HMA domain containing heavy metal-binding sites, which may play a role in transporting or detoxifying heavy metals.

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Background: Desquamation interstitial pneumonia (DIP) is a rare type of idiopathic interstitial pneumonia. High resolution computed tomography (HRCT) shows ground glass opacities without the peripheral reticular opacities characteristic of usual interstitial pneumonia (UIP). Here we report a case of DIP presenting as a solid mass in the lung, which is rarely described in the literature.Case presentation: A 77-year-old man presented with dry cough and dyspnea on exertion for one month was admitted to our hospital. The lung CT scan showed there was a pulmonary mass in right lower lung and the patient was scheduled for surgery. He was a sculpture artist, non-smoker and the previous medical history included only mandatory spondylitis without other connective tissue diseases. Nine days post-last CT, the FDG PET/CT demonstrated the mass in the right lower lung was significantly hypermetabolic (SUV value=8.9) but inflammatory exudate could be observed around the mass. We gave antibiotics and performed CT-guided percutaneous lung biopsy. The result showed that there were a large number of macrophages in the alveolar cavity, alveolar epithelial type II cells hyperplasia in some areas and chronic inflammation was noted in the interstitium. Then the desquamative interstitial pneumonia was diagnosed. We gave the patient glucocorticoid therapy, then the patient's symptoms disappeared gradually and the lung CT showed that the pulmonary mass was disappeared.Conclusions: Our report illustrates the rare presentation of DIP. Furthermore, for the pulmonary mass, even if appeared hypermetabolic on PET/CT, it is still necessary to make a definite pathological diagnosis before operation, so as to reduce the damage to patients.