OLIVE PRUNING WASTE CONVERSION INTO VALUE-ADDED LIPIDS BY Rhodococcus

SANDOVAL NATALIA; ARIAS NADIA SOLEDAD; GALLEGOS LAURA; PALMERI MARCELA AILÉN; ÁLVAREZ HÉCTOR; LANFRANCONI MARIANA

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Oliveoil industry produces many by-products among which, tree leavesrepresenta massive waste. Olive leaves couldbe obtained at the early stages of olivefruit cleaning or during pruning practice to remove old branches and increasecrop productivity. They have no economical value and are usually burned or usedas animal feed. Our objective was to evaluate the potential use of this wasteto generate lipids of biotechnological interestin bacteria. Furthermore, ourapproachwould help to solve an environmental problem related to its disposal;it´s known that around 3 tons of olive pruning is generated from a hectare ofolive orchard.Bacterial strains used included anoleaginous paradigm (Rhodococcus opacus PD630), a representative of a potentialplant pathogen (Rhodococcus fascians F7), an efficient industrial waste bioconverter(RhodococcuserythropolisDSM43060),and an isolate obtained from olive leaves(Rhodococcus sp. 24CO). Leaves  from olivetrees (var. Frantoio)were collectedin the Jardín Varietal de Olivos “Patagonia Sur”located at National Universityof Patagonia San Juan Bosco.(45º 47’S, 67º30’O). Four different culturemedia containingsolid raw waste (RW) or liquid residue (Tea)prepared from fresh(F) or dewatered (DW) leaves weretested for growth and lipid accumulation in thesestrains.Before inoculation, different chemical parameters were analyzed in eachculture media and based on the values obtained, those prepared from tea (F orDW)were the best candidates for lipid production due to the high C/N ratio theyshowed. Total sugar values of ~20 g L-1 were similar among the mediatested except for FRW whose value triplicated the content in comparison withthe other media.Bacterial growth was estimated by measuring OD 600 nm andshowed 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 inalmost all media tested. Largely characterized strains such as R. opacus PD630and R. erythropolisDSM43060showed similar dynamics reaching intermediate growthvalues while for R. fascians F7, the values obtained were low or near zero. Theability to accumulate neutral lipids such as triacylglycerols (TAG)was alsoanalyzedfor each media and strain that showed growth. Our results indicate thatthe most efficient media that favored lipid accumulation were FRW and FTea with total fatty acid contents of37.4 and 51.9% w/w in R. opacus,respectively. Interestingly,strain 24CO was also highly efficient inconverting 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 includedpalmitic (C16:0), palmitoleic (C16:1) acids and in lower amount, stearic(C18:0) and oleic (C18:1) fattyacids.In both media, in R. sp. 24CO was represented by palmitic (C16:0),stearic (C18:0) and oleic (C18:1) acids. These fatty acids have multipleapplications and could interested different industrial fields. Thus,olive treeleaves generated as a by-product of the oil industry could be a highly-valuedwaste to the economy as well as to the environment.