Engineered cyanobacteria as promising platform for sustainable 2-phenylethanol production.

The resilience and recovery strategies implemented by European Union countries have as key pillars the reduction of environmental impacts and waste valorisation. In this context, biotechnological approaches based on cyanobacteria offer great potential as biocatalyst for CO₂ conversion into a plethora of added-value compounds. By a combined approach of metabolite doping and metabolic engineering, we developed and optimized an efficient microbial platform based on engineered <em>Synechococcus elongatus</em> PCC 7942 for the production of 2-phenilethanol (2-PE), a high-value aromatic rose-scented compound, exploitable in the food, fragrance and flavour industries. The success of our strategy lies on the compensation of the metabolic burden by implementing a BG11 medium doped with L-phenylalanine and on the overexpression of a key endogenous gene (i.e. shikimate synthase) of the shikimate pathway involved in the synthesis of 2-PE precursors. Thus, we obtained a maximum 2-PE titer of 285 mg/L, the highest recorded so far for photosynthetic microorganisms in autotrophic condition. Moreover, in order to make the process sustainable, we essayed the exploitation of wastewater (WW) as growth substrate. We screened several WWs from the dairy manufacturing, a major industrial contributor to water pollution due to the large volume and high nutrient load of its effluents. Our trials showed the possibility of fully support the growth of engineered strain by balancing dairy washing water and digestate, confirming the potential of cyanobacteria as sustainable green factories.