Construction of Lactobacillus plantarum strain with enhanced L-lysine yield

Rapid Revealing of Quorum Sensing (QS)-Regulated PLA, Biofilm and Lysine Targets of Lactiplantibacillus plantarum L3

Quorum sensing (QS) can regulate the production of multiple functional factors in bacteria, but the process of identifying its regulatory targets is very complex and labor-intensive. In this study, an efficient and rapid method to find QS targets through prediction was used. The genome of Lactiplantibacillus plantarum (L. plantarum) L3 was sequenced and characterized, and then linked the L. plantarum L3 genome to the STRING database for QS system regulatory target prediction. A total of 3,167,484 base pairs (bps) were examined from the genome of L. plantarum L3, and 30 QS-related genes were discovered (including luxS). The STRING database prediction indicated that the 30 QS-related genes are mainly involved in the regulation of nine metabolic pathways. Furthermore, metE, metK, aroB, cysE, and birA1 were predicted to be regulatory targets of the LuxS/AI-2 QS system, and these five targets were validated based on quantitative real-time PCR and content determination. Successful elucidation of the LuxS/AI-2 QS system's key targets and regulation mechanism in L. plantarum L3 demonstrated the effectiveness of the new approach for predicting QS targets and provides a scientific basis for future work on improving regulation of functional factor production.

Structural-functional analysis of drug target aspartate semialdehyde dehydrogenase

Aspartate β-semialdehyde dehydrogenase (ASADH) is a key enzyme in the biosynthesis of essential amino acids in microorganisms and some plants. Inhibition of ASADHs can be a potential drug target for developing novel antimicrobial and herbicidal compounds. This review covers up-to-date information about sequence diversity, ligand/inhibitor-bound 3D structures, potential inhibitors, and key pharmacophoric features of ASADH useful in designing novel and target-specific inhibitors of ASADH. Most reported ASADH inhibitors have two highly electronegative functional groups that interact with two key arginyl residues present in the active site of ASADHs. The structural information, active site binding modes, and key interactions between the enzyme and inhibitors serve as the basis for designing new and potent inhibitors against the ASADH family.

Colorimetric ortho-aminobenzaldehyde assay developed for the high-throughput chemical screening of inhibitors against dihydrodipicolinate synthase from pathogenic bacteria

In search of a new class of antibacterial agents, compounds that target the essential bacterial enzyme, dihydrodipicolinate synthase (DHDPS), are of interest to drug discovery efforts. DHDPS catalyzes the first committed step in the diaminopimelate (DAP) pathway to the biosynthesis of lysine in bacteria and plants. The ortho-aminobenzaldehyde (o-ABA) assay is typically used as a qualitative tool for identifying fractions containing DHDPS during purification. This report is about the development of a high-throughput o-ABA assay format for the quantification of DHDPS enzyme activity using multi-well plates. The colorimetric assay is suitable for determining enzymatic parameters (K _M and V_max) and identifying inhibitors of DHDPS in a high-throughput screen.

Nanocrystalline Cellulose Cures Constipation via Gut Microbiota Metabolism

Constipation can seriously affect the quality of life and increase the risk of colorectal cancer. The present strategies for constipation therapy have adverse effects, such as causing irreversible intestinal damage and affecting the absorption of nutrients. Nanocrystalline cellulose (NCC), which is from natural plants, has good biocompatibility and high safety. Herein, we used NCC to treat constipation assessed by the black stool, intestinal tissue sections, and serum biomarkers. We studied the effect of NCC on gut microbiota and discussed the correlation of gut microbiota and metabolites. We evaluated the long-term biosafety of NCC. NCC could effectively treat constipation through gut microbiota metabolism, which required a small dosage and did not affect the organs and intestines. NCC could be used as an alternative to medications and dietary fiber for constipation therapy.

Rational modification of Corynebacterium glutamicum dihydrodipicolinate reductase to switch the nucleotide-cofactor specificity for increasing l-lysine production

l-lysine is an important amino acid in animals and humans and NADPH is a vital cofactor for maximizing the efficiency of l-lysine fermentation. Dihydrodipicolinate reductase (DHDPR), an NAD(P)H-dependent enzyme, shows a variance in nucleotide-cofactor affinity in bacteria. In this study, we rationally engineered Corynebacterium glutamicum DHDPR (CgDHDPR) to switch its nucleotide-cofactor specificity resulting in an increase in final titer (from 82.6 to 117.3 g L^-1 ), carbon yield (from 0.35 to 0.44 g [g glucose]^-1 ) and productivity (from 2.07 to 2.93 g L^-1  hr^-1 ) of l-lysine in JL-6 ΔdapB::Ec-dapB^C115G,G116C in fed-batch fermentation. To do this, we comparatively analyzed the characteristics of CgDHDPR and Escherichia coli DHDPR (EcDHDPR), indicating that hetero-expression of NADH-dependent EcDHDPR increased l-lysine production. Subsequently, we rationally modified the conserved structure of cofactor-binding motif, and results indicated that introducing the mutation K11A or R13A in CgDHDPR and introducing the mutation R16A or R39A in EcDHDPR modifies the nucleotide-cofactor affinity of DHDPR. Lastly, the effects of these mutated DHDPRs on l-lysine production were investigated. The highest increase (26.2%) in l-lysine production was observed for JL-6 ΔdapB::Ec-dapB^C115G,G116C , followed by JL-6 Cg-dapB^C37G,G38C (21.4%) and JL-6 ΔdapB::Ec-dapB^C46G,G47C (15.2%). This is the first report of a rational modification of DHDPR that enhances the l-lysine production and yield through the modulation of nucleotide-cofactor specificity.

Analysis and manipulation of aspartate pathway genes for L-lysine overproduction from methanol by Bacillus methanolicus

We investigated the regulation and roles of six aspartate pathway genes in L-lysine overproduction in Bacillus methanolicus: dapG, encoding aspartokinase I (AKI); lysC, encoding AKII; yclM, encoding AKIII; asd, encoding aspartate semialdehyde dehydrogenase; dapA, encoding dihydrodipicolinate synthase; and lysA, encoding meso-diaminopimelate decarboxylase. Analysis of the wild-type strain revealed that in vivo lysC transcription was repressed 5-fold by L-lysine and induced 2-fold by dl-methionine added to the growth medium. Surprisingly, yclM transcription was repressed 5-fold by dl-methionine, while the dapG, asd, dapA, and lysA genes were not significantly repressed by any of the aspartate pathway amino acids. We show that the L-lysine-overproducing classical B. methanolicus mutant NOA2#13A52-8A66 has-in addition to a hom-1 mutation-chromosomal mutations in the dapG coding region and in the lysA promoter region. No mutations were found in its dapA, lysC, asd, and yclM genes. The mutant dapG gene product had abolished feedback inhibition by meso-diaminopimelate in vitro, and the lysA mutation was accompanied by an elevated (6-fold) lysA transcription level in vivo. Moreover, yclM transcription was increased 16-fold in mutant strain NOA2#13A52-8A66 compared to the wild-type strain. Overexpression of wild-type and mutant aspartate pathway genes demonstrated that all six genes are important for L-lysine overproduction as tested in shake flasks, and the effects were dependent on the genetic background tested. Coupled overexpression of up to three genes resulted in additive (above 80-fold) increased L-lysine production levels.