meso -Diaminopimelate dehydrogenase ( meso -DAPDH) is an NADP ⁺ -dependent enzyme which catalyzes the reversible oxidative deamination on the d -configuration of meso -2,6-diaminopimelate to produce l -2-amino-6-oxopimelate. In this study, the gene encoding a meso -diaminopimelate dehydrogenase from Symbiobacterium thermophilum was cloned and expressed in Escherichia coli . In addition to the native substrate meso -2,6-diaminopimelate, the purified enzyme also showed activity toward d -alanine, d -valine, and d -lysine. This enzyme catalyzed the reductive amination of 2-keto acids such as pyruvic acid to generate d -amino acids in up to 99% conversion and 99% enantiomeric excess. Since meso -diaminopimelate dehydrogenases are known to be specific to meso -2,6-diaminopimelate, this is a unique wild-type meso -diaminopimelate dehydrogenase with a more relaxed substrate specificity and potential for d -amino acid synthesis. The enzyme is the most stable meso -diaminopimelate dehydrogenase reported to now. Two amino acid residues (F146 and M152) in the substrate binding sites of S. thermophilum meso -DAPDH different from the sequences of other known meso -DAPDHs were replaced with the conserved amino acids in other meso -DAPDHs, and assay of wild-type and mutant enzyme activities revealed that F146 and M152 are not critical in determining the enzyme's substrate specificity. The high thermostability and relaxed substrate profile of S. thermophilum meso -DAPDH warrant it as an excellent starting enzyme for creating effective d -amino acid dehydrogenases by protein engineering.

Inflammation is the body’s defense reaction in response to stimulations and is the basis of various physiological and pathological processes. However, chronic inflammation is undesirable and closely related to the occurrence and development of diseases. The ocean gives birth to unique and diverse bioactive substances, which have gained special attention and been a focus for anti-inflammatory drug development. So far, numerous promising bioactive substances have been obtained from various marine organisms such as marine bacteria and fungi, sponges, algae, and coral. This review covers 71 bioactive substances described during 2015–2020, including the structures (65 of which), species sources, evaluation models and anti-inflammatory activities of these substances. This review aims to provide some reference for the research progress of marine-organism-derived anti-inflammatory metabolites and give more research impetus for their conversion to novel anti-inflammatory drugs.

In order to enlarge the substrate binding pocket of the meso -diaminopimelate dehydrogenase from Symbiobacterium thermophilum to accommodate larger 2-keto acids, four amino acid residues (Phe146, Thr171, Arg181, and His227) were targeted for site saturation mutagenesis. Among all mutants, the single mutant H227V had a specific activity of 2.39 ± 0.06 U · mg ⁻¹ , which was 35.1-fold enhancement over the wild-type enzyme.

Surfactin is widely used in the petroleum extraction, cosmetics, biopharmaceuticals and agriculture industries. It possesses antibacterial and antiviral activities and can reduce interfacial tension. Bacillus are commonly used as production chassis, but wild-type Bacillus subtilis 168 cannot synthesise surfactin. In this study, the phosphopantetheinyl transferase (PPTase) gene sfp* (with a T base removed) was overexpressed and enzyme activity was restored, enabling B. subtilis 168 to synthesise surfactin with a yield of 747.5 ± 6.5 mg/L. Knocking out ppsD and yvkC did not enhance surfactin synthesis. Overexpression of predicted surfactin transporter gene yfiS increased its titre to 1060.7 ± 89.4 mg/L, while overexpression of yerP, ycxA and ycxA-efp had little or negative effects on surfactin synthesis, suggesting YfiS is involved in surfactin efflux. By replacing the native promoter of the srfA operon encoding surfactin synthase with three promoters, surfactin synthesis was significantly reduced. However, knockout of the global transcriptional regulator gene codY enhanced the surfactin titre to 1601.8 ± 91.9 mg/L. The highest surfactin titre reached 3.89 ± 0.07 g/L, with the yield of 0.63 ± 0.02 g/g DCW, after 36 h of fed-batch fermentation in 5 L fermenter. This study provides a reference for further understanding surfactin synthesis and constructing microbial cell factories.