Transfer of the high-GC cyclohexane carboxylate degradation pathway from Rhodopseudomonas palustris to Escherichia coli for production of biotin

Advances in biotin biosynthesis and biotechnological production in microorganisms

Biotin, also known as vitamin H or B7, acts as a crucial cofactor in the central metabolism processes of fatty acids, amino acids, and carbohydrates. Biotin has important applications in food additives, biomedicine, and other fields. While the ability to synthesize biotin de novo is confined to microorganisms and plants, humans and animals require substantial daily intake, primarily through dietary sources and intestinal microflora. Currently, chemical synthesis stands as the primary method for commercial biotin production, although microbial biotin production offers an environmentally sustainable alternative with promising prospects. This review presents a comprehensive overview of the pathways involved in de novo biotin synthesis in various species of microbes and insights into its regulatory and transport systems. Furthermore, diverse strategies are discussed to improve the biotin production here, including mutation breeding, rational metabolic engineering design, artificial genetic modification, and process optimization. The review also presents the potential strategies for addressing current challenges for industrial-scale bioproduction of biotin in the future. This review is very helpful for exploring efficient and sustainable strategies for large-scale biotin production.

Genetic characterization of the cyclohexane carboxylate degradation pathway in the denitrifying bacterium Aromatoleum sp. CIB

The alicyclic compound cyclohexane carboxylate (CHC) is anaerobically degraded through a peripheral pathway that converges with the central benzoyl-CoA degradation pathway of aromatic compounds in Rhodopseudomonas palustris (bad pathway) and some strictly anaerobic bacteria. Here we show that in denitrifying bacteria, e.g. Aromatoleum sp. CIB strain, CHC is degraded through a bad-ali pathway similar to that reported in R. palustris but that does not share common intermediates with the benzoyl-CoA degradation pathway (bzd pathway) of this bacterium. The bad-ali genes are also involved in the aerobic degradation of CHC in strain CIB, and orthologous bad-ali clusters have been identified in the genomes of a wide variety of bacteria. Expression of bad-ali genes in strain CIB is under control of the BadR transcriptional repressor, which was shown to recognize CHC-CoA, the first intermediate of the pathway, as effector, and whose operator region (CAAN₄ TTG) was conserved in bad-ali clusters from Gram-negative bacteria. The bad-ali and bzd pathways generate pimelyl-CoA and 3-hydroxypimelyl-CoA, respectively, that are metabolized through a common aab pathway whose genetic determinants form a supraoperonic clustering with the bad-ali genes. A synthetic bad-ali-aab catabolic module was engineered and it was shown to confer CHC degradation abilities to different bacterial hosts.