High L(+)-lactic acid productivity in continuous fermentations using bakery waste and lucerne green juice as renewable substrates.

The biotechnological production of platform chemicals from renewable resources is in the scientific spotlight, as researchers seek to develop environmentally friendly and cost-efficient processes to compete with the petroleum-based ones. Lactic acid (LA) is an established platform chemical, registering an important market share, mainly owing to the increasing demand for polylactic acid. This study investigated the feasibility to produce LA from bakery waste hydrolysates and lucerne green juice (LGJ) as inexpensive substrates, using a Bacillus coagulans strain. A final LA concentration of 62.2 g/L, with a productivity of 2.59 g/(L.h) and a conversion yield of 0.57 g LA/ g bakery waste was achieved in batch fermentation mode. LA productivity reached 11.28 g/(L.h), using a continuous fermentation system coupled with cell retention membranes at a dilution rate of 0.2 h-1. The results indicate that bakery waste hydrolysates and LGJ can be utilized for the production of highly optical pure L(+)-LA.

cAMP-CRP co-ordinates the expression of the protein acetylation pathway with central metabolism in Escherichia coli.

Lysine acetylation is a well-established post-translational modification widely conserved and distributed in bacteria. Although multiple regulatory roles have been proved, little is known about its regulation. Here, we present evidence that the transcription of the Gcn5-like acetyltransferase YfiQ of Escherichia coli (proposed name: PatZ) is regulated by cAMP-CRP and its implications on acetate metabolism regulation. The acetate scavenging acetyl-CoA synthetase (Acs) is regulated at the transcriptional and post-translational levels. Post-translational regulation depends on a protein acetyltransferase (yfiQ) and an NAD(+) -dependent deacetylase (cobB). We have studied their expression under different environmental conditions. cobB is constitutively expressed from a promoter located upstream nagK. The expression of yfiQ occurs from its own promoter; it is upregulated in the stationary phase and in the presence of non-PTS carbon sources and is positively regulated by cAMP-CRP. Two putative CRP binding sites are necessary for its full activity. Gene deletion revealed that cobB is essential for growth on acetate, yfiQ deletion restoring growth of the cobB mutant. The fine tuning of metabolic enzymes results from the integration of multiple mechanisms, and redundant systems may exist. Despite the existence of divergent catabolite repression systems, this may be a conserved strategy common to both Gram-positive and -negative bacteria.