Recombinant Lactococcus lactis for efficient conversion of cellodextrins into L‐lactic acid

Abstract

Lactic acid bacteria (LAB) are among the most interesting organisms for industrial processes with a long history of application as food starters and biocontrol agents, and an underexploited potential for biorefineries converting biomass into high-value compounds. Lactic acid (LA), their main fermentation product, is among the most requested chemicals owing to its broad range of applications. Notably, LA polymers, that is, polylactides, have high potential as biodegradable substitutes of fossil-derived plastics. However, LA production by LAB fermentation is currently too expensive for polylactide to be cost-competitive with traditional plastics. LAB have complex nutritional requirements and cannot ferment inexpensive substrates such as cellulose. Metabolic engineering could help reduce such nutritional requirements and enable LAB to directly ferment low-cost polysaccharides. Here, we engineered a Lactococcus lactis strain which constitutively secretes a β-glucosidase and an endoglucanase. The recombinant strain can grow on cellooligosaccharides up to at least cellooctaose and efficiently metabolizes them to L-LA in single-step fermentation. This is the first report of a LAB able to directly metabolize cellooligosaccharides longer that cellohexaose and a significant step toward cost-sustainable consolidated bioprocessing of cellulose into optically pure LA.

Alternative strategies for lignocellulose fermentation through lactic acid bacteria: the state of the art and perspectives

“…lactis IL1403, i.e. one of the very reference LAB strains, has shown the natural ability to ferment up to cellotetraose/cellopentaose (Gandini et al 2017). This study has indicated that this strain is equipped with membrane transporters for short cellodextrins, although they have not been identified yet.…”

“…Forefront research in development of 2 nd generation biorefinery includes endowing microorganisms that produce high-value chemicals with the ability to directly ferment lignocellulose without prior physico-chemical and/or enzymatic pre-treatment through recombinant techniques (Mazzoli et al 2012). The number of examples of recombinant cellulolytic strategies (RCS) addressed to LAB is growing (Mazzoli et al 2014;Gandini et al 2017;Stern et al 2018).…”

Construction of lactic acid overproducing Clostridium thermocellum through enhancement of lactate dehydrogenase expression

“…Development of such CBP could significantly reduce the current cost of LA. Most previous metabolic engineering strategies aimed at direct fermentation of lignocellulose to LA have attempted to introduce (hemi)cellulolytic characteristics in natural producers of LA [30,31]. The approach used in the present study focused on improving the expression of the native LDH of the cellulolytic bacterium C. thermocellum DSM1313 by functionally replacing its native promoter with stronger ones.…”

Lactic Acid Production from Lignocellulose – A Review of Major Challenges and Selected Solutions

“…A L. lactis strain that secreted endoglucanase and β ‐glucosidase was developed through the construction of an artificial operon. This strain was able to metabolize cellooctaose to L ‐LA .…”