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Processes for Overproduction of Microbial Metabolites for Industrial Applications
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Both protein synthesis and RNA synthesis stop when an amino acid requiring mutant exhausts the amino acid supplied to it in the medium. In this way, the cell avoids the overproduction of unwanted RNA. Such economical strains are ‘stringent’. However, certain mutant strains are ‘relaxed’ and continue to produce RNA in the absence of the required amino acid. The stoppage of RNA synthesis in stringent strains is due to the production of the nucleotide guanosine tetraphosphate and guanosine pentaphosphate when the supplied amino acid becomes limiting. The amount of nucleotide guanosine tetraphosphate or nucleotide guanosine pentaphosphate in the cell is inversely proportional to the amount of RNA and the rate of growth.
Formation mechanisms of viable but nonculturable bacteria through induction by light-based disinfection and their antibiotic resistance gene transfer risk: A review
Published in Critical Reviews in Environmental Science and Technology, 2021
Yiwei Cai, Jianying Liu, Guiying Li, Po Keung Wong, Taicheng An
Formation mechanisms of VBNC bacteria are still the focus of current research. The stringent response mechanism occurs after bacteria or plants receive an amino acid starvation signal mediated by the alarmone, guanosine tetraphosphate and guanosine pentaphosphate (collectively referred to as (p)ppGpp). There is evidence that E. coli mutants that cannot produce ppGpp are less likely to be induced into VBNC bacteria, while bacteria that overproduce ppGpp are more likely to be induced to the VBNC state (Boaretti et al., 2003). This means that the stringent response plays an important role in the formation of VBNC bacteria (Figure 2). VBNC V. cholerae O1, was found to have highly up-regulated expression of the relA gene, which is involved in the stringent response signaling pathway. RelA catalyzes the synthesis of ppGpp and causes it to accumulate in the cell, which in turn affects the synthesis of DNA, RNA and proteins, leading to growth arrest (Mishra et al., 2012). The general stress response system, mainly controlled by RNA polymerase σS (RpoS) and LysR transcription regulator (OxyR), also plays an important role in the induction and formation of VBNC bacteria (Boaretti et al., 2003; Liao et al., 2019). The rpoS gene is important for activating the formation of VBNC bacteria and acts as the main signal to regulate the stress response factor. RpoS endows bacteria with tolerance to a variety of environment stressors, while OxyR is mainly involved in the process that allows bacteria to deal with oxidative stress. Evidence suggests that OxyR is an important regulatory protein, and its absence causes the VBNC state in many bacteria such as S. typhimurium (Liao et al., 2019). The transcription and translation of rpoS is regulated by ppGpp, and downstream rpoS further encodes the sigma factor (Figure 2) (Boaretti et al., 2003).