Growth of Escherichia coli cells in the presence of cysteine on sulphate-deficient media

Systemic intracellular analysis for balancing complex biosynthesis in a transcriptionally deregulated Escherichia coli l-Methionine producer

l-Methionine (l-Met) has gained remarkable interest due to its multifaceted and versatile applications in the fields of nutrition, pharmaceuticals and clinical practice. In this study, the fluxes of the challenging l-Met biosynthesis in the producer strain Escherichia coli (E. coli) DM2853 were fine-tuned to enable improved l-Met production. The potential bottlenecks identified in sulfur assimilation and l-Met synthesis downstream of O-succinyl-l-homoserine (OSHS) were addressed by overexpressing glutaredoxin 1 (grxA), thiosulfate sulfurtransferase (pspE) and O-succinylhomoserine lyase (metB). Although deemed as a straightforward target for improving glucose-to-Met conversion, the yields remained at approximately 12%-13% (g/g). Instead, intracellular l-Met pools increased by up to four-fold with accelerated kinetics. Overexpression of the Met exporter ygaZH may serve as a proper valve for releasing the rising internal Met pressure. Interestingly, the export kinetics revealed maximum saturated export rates already at low growth rates. This scenario is particularly advantageous for large-scale fermentation when product formation is ideally uncoupled from biomass formation to achieve maximum performance within the technical limits of large-scale bioreactors.

Enhancing the AI-2/LuxS quorum sensing system in Lactiplantibacillus plantarum: Effect on the elimination of biofilms grown on seafoods

The biofilm clustered with putrefying microorganisms and seafood pathogens could cover the surface of aquatic products that pose a risk to cross-contaminating food products or even human health. Fighting biofilms triggers synchronous communication associated with microbial consortia to regulate their developmental processes, and the enhancement of the quorum sensing system in Lactiplantibacillus plantarum can serve as an updated starting point for antibiofilm-forming strategies. Our results showed that the exogenous 25 mM L-cysteine induced a significant strengthening in the AI-2/LuxS system of Lactiplantibacillus plantarum SS-128 along with a stronger bacteriostatic ability, resulting in an effective inhibition of biofilms formed by the simplified microbial consortia constructed by Vibrio parahaemolyticus and Shewanella putrefaciens grown on shrimp and squid surfaces. The accumulation of AI-2 allowed the suppression of the expression of biofilm-related genes in V. parahaemolyticus under the premise of L. plantarum SS-128 treatment, contributing to the inhibition effect. In addition, strengthening the AI-2/LuxS system is also conducive to eliminating preexisting biofilms by L. plantarum SS-128. This study suggests that the enhancement of the AI-2/LuxS system of lactic acid bacteria enables the regulation of interspecific communication within biofilms to be a viable tool to efficiently reduce and eradicate potentially harmful biofilms from aquatic product sources, opening new horizons for combating biofilms.

Study of growth requirements other than cysteine of naturally occurring Escherichia coli and Klebsiella spp. auxotrophic for cysteine

Cysteine remains the preferred supplement for cultivation of Cys- auxotrophs in vitro. Methionine, which reduced cysteine requirements, and branched-chain amino acids, which decreased cysteine toxicity, were identified as the components of casein hydrolysate responsible for growth enhancement by this additive. Glutathione and DL-homocysteine can be substituted for cysteine. Accumulation of these compounds in patients with renal impairment may favor selection of Cys- strains in vivo.

Assessment of conventional and commercial methods for identification of clinical isolates of cysteine-requiring strains of Escherichia coli and Klebsiella species

Cysteine-requiring strains of the family Enterobacteriaceae that are auxotrophic for this amino acid because of defects in the sulfur assimilatory pathway account for about 1.5% of urinary tract isolates of Escherichia coli and Klebsiella species. Forty Escherichia and eight Klebsiella cysteine-requiring strains were used to test the ease with which various test systems identified clinical isolates of cysteine auxotrophs. In a preliminary experiment, the growth yield of 10 cysteine-requiring E. coli in 10 solutions of commercially available peptones was in each instance less than that of prototrophic control and showed that these sources of nutrients were suboptimal for these strains. A significant proportion of the cysteine-requiring strains were not adequately identified by growth-dependent tests which used various peptones as a nutrient source. Problems were encountered with all test systems examined, which were as follows: conventional methods; the API 20E, Microbact, and Vitek systems; and two rapid methods for the identification of E. coli, the Rapidec coli and the beta-D-glucuronidase tests. The performance of the test systems was only partly improved when inocula were derived from appropriately supplemented media. However, the problems of the growth-dependent tests were resolved when a cysteine-supplemented suspension was used to inoculate each test system.

Cysteine requirements of naturally occurring cysteine auxotrophs of Escherichia coli

The requirements for cysteine of naturally occurring cysteine auxotrophs of Escherichia coli were determined in a defined liquid medium. Maximal growth was obtained in the presence of cysteine concentrations between 20 and 250 mg/l. At concentrations below 20 mg/l growth of the auxotrophs, but not the prototrophic control, was suboptimal in this system. In the presence of cysteine concentrations in excess of 250 mg/l, growth of both auxotrophic and prototrophic E. coli was inhibited with lower growth yields, a decreased specific growth rate and an extended lag phase being observed. These effects were minimised in the presence of 2 mM L-leucine, L-isoleucine and L-valine.

Incorporation of specifically labeled cysteine into Escherichia coli protein

Protein obtained from several strains of Escherichia coli grown in the presence of [3,3'-14C]cystine contained the radiolabel in nearly all the other amino acids, suggesting catabolism of cysteine to pyruvic acid. Utilization in amino acid synthesis of the pyruvate thus generated can be blocked by growing the bacteria in a medium specifically enriched with most of the naturally occurring amino acids. Cysteine that is incorporated intact is diluted by de novo synthesis at low cystine concentrations; also, it was found that E. coli can use the sulfur of methionine for cysteine biosynthesis. Both of these latter two processes can be prevented by supplying an excess of exogenous cystine. This regimen leads to protein that is highly specifically labeled in the cysteine residues, with a minor amount (20-25%) of the label also appearing in alanine residues. Although this strategy was developed expressly for cysteine, it may be useful for incorporating other labeled amino acids that are also readily catabolized.