Olive pruning waste conversion into value-added lipids by Rhodococcus

SANDOVAL NATALIA; ARIAS NADIA; GALLEGOS LAURA; PALMERI AILEN; ALVAREZ HECTOR; LANFRANCONI MARIANA

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Olive oil industry produces many by-products among which, tree leaves represent a massive waste. Olive leaves could be obtained at the early stages of olive fruit cleaning or during pruning practice to remove old branches and increase crop productivity. They have no economic value and are usually burned or used as animal feed. Our objective was to evaluate the potential of this waste to generate lipids of biotechnological interest in bacteria. Furthermore, our approach would help to solve an environmental problem related to its disposal. Bacterial strains used included an oleaginous paradigm (Rhodococcus opacus PD630), a representative of a potential plant pathogen (Rhodococcus fascians F7), an efficient industrial waste bioconverter (Rhodococcus erythropolis DSM43060), and an isolate obtained from olive leaves (Rhodococcus sp. 24CO). Leaves from olive trees (var. Frantoio) were collected in the Jardín Varietal de Olivos “Patagonia Sur´´ located at UNPSJB (45º 47’S, 67º30’O). different culture media containing solid raw waste (RW) or liquid residue (Tea) prepared from fresh (F) or dewatered (DW) leaves were tested for growth and lipid accumulation in these strains. Before inoculation, different chemical parameters were analyzed in each culture media and based on the values obtained, those prepared from tea (F or DW) were the best candidates for lipid production due to the high C/N ratio they showed. Total sugar values were similar among the media tested except for FRW whose value triplicated the content in comparison with the other media. Bacterial growth was estimated by measuring OD 600 nm and showed the highest values in FRW medium. The strains exhibited different growth behaviors with R. sp. 24CO being able to grow in every media and reaching the highest values in almost all media tested. Largely characterized strains such as R. opacus PD630 and R. erythropolis DSM43060 showed similar dynamics reaching intermediate growth values while for R. fascians F7, the values obtained were low or near zero. The ability to accumulate neutral lipids was also analyzed for each media and strain that showed growth. Our results indicate that the most efficient media that favored lipid accumulation were FRW and FTea with total fatty acid contents of 37.4 and 51.9% w/w in R. opacus, respectively. Interestingly, strain 24CO was also highly efficient in converting the residue to neutral lipids with values of 20.2 and 26.2% (w/w) when grown on those media. The main fatty acids found in R. opacus PD630 included palmitic (C16:0), palmitoleic (C16:1) acids and in lower amount, stearic (C18:0) and oleic (C18:1) fatty acids. In both media, in R. sp. 24CO was represented by palmitic, stearic and oleic acids. These fatty acids have multiple applications and could interest different industrial fields. Thus, olive tree leaves generated as a by-product of the oil industry could be a highly-valued waste to the economy as well as to the environment.