The present invention provides a 5-methylfolate producing microorganism which a) has been modified to have a decreased expression and/or activity of a polypeptide having both dihydrofolate synthase activity and folylpolyglutamate synthetase activity compared to an otherwise identical microorganism (reference microorganism); b) has been (further) modified to express a heterologous polypeptide having only dihydrofolate synthase activity; c) has been (further) modified to have an increased expression level of at least one enzyme (such as at least two, at least three, at least four, at least five, at least six, at least seven or at least eight) enzymes involved in the biosynthesis of a 5-methylfolate compared to an otherwise identical microorganism (reference microorganism); and/or d) has been (further) modified to have a decreased expression and/or activity of a polypeptide having 5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase activity compared to an otherwise identical microorganism (reference microorganism).

A method is described for producing L-methionine by fermentation using a bacterium which has been modified to overexpress a 1st gene and a 2nd gene, such as genes having the nucleotide sequences shown in SEQ ID NOs: 1 and 3.

A bacterial host cell is disclosed including at least two copies of an amplification unit in its genome, the amplification unit including: i) at least one copy of a gene of interest, and ii) an expressible conditionally essential gene, wherein the conditionally essential gene is either promoterless or transcribed from a heterologous promoter having an activity substantially lower than the endogenous promoter of the conditionally essential gene, and wherein the conditionally essential gene if not functional would render the cell auxotrophic for at least one specific substance or unable to utilize one or more specific sole carbon source; methods for producing a protein using the cell of the invention, and methods for constructing the cell of the invention.

The present invention discloses a genetically engineered bacterium using glucose as a substrate for de novo synthesis of vanillin and an application thereof, which belongs to the technical field of gene recombination and metabolic engineering. The genetically engineered bacterium using the glucose as the substrate for de novo synthesis of vanillin disclosed by the present invention is recombinant Corynebacterium glutamicum modified by chassis microorganisms and including a vanillin synthesis module and a methyl cyclic regeneration module. The genetically engineered bacteria constructed by the present invention are safe and non-toxic, can use the glucose for de novo synthesis of natural vanillin, and is low in production cost, high in yield, and promising in application prospect.

Provided herein are genetically modified host cells, compositions, and methods for improved production of vanillin and/or glucovanillin. The host cells, compositions, and methods described herein provide an efficient route for the heterologous production of vanillin and/or glucovanillin and any compound that can be synthesized or biosynthesized from either or both.