Constantinos Balis

Edible mushrooms from olive oil mill wastes

Abstract The biological remediation of olive oil mill wastes has been attempted several times in the past through the use of different types of microbes. Among them, a relatively large array of fungi were studied for neutralizing the heavy pollutant effects and/or for converting these wastes into new value-added products. The present investigation was aiming at examining whether olive oil mill wastes could be exploited for the cultivation of mushrooms of the genus Pleurotus . At a preliminary stage, two Pleurotus species, i.e. P. eryngii and P. pulmonarius , were tested for their ability to colonize an olive press-cake (OPC) substrate supplemented with various dilutions of raw olive mill wastewater (OWW). Some important cultural characters related to mushroom production (earliness, yield, biological efficiencies and quality of basidiomata) were estimated. The outcome revealed different cultural responses for each Pleurotus species examined; the P. pulmonarius strain showed better earliness values and P. eryngii , although it was a slow growing fungus, produced basidiomata in high yields and of a very good quality. On the other hand, the OPC substrate supplemented with low concentrations of OWW (12.5% v/w) behaved satisfactorily as regards the fungal colonization rates and mushroom yield, but when the addition of higher rates of raw, untreated OWW (75–100% v/w) was attempted then the Pleurotus strains were completely unable to grow. The optimal concentration of OWW for Pleurotus mycelial growth was assessed through measurements of the biomass produced in liquid nutrient media and was found to lie within the 25–50% range, depending on the Pleurotus species and on the properties of the substrates examined. Furthermore, the phytotoxic effects that the spent liquid medium possessed were examined in comparison with the phytotoxicity of the raw liquid waste. The prospects of exploiting olive oil mills wastes for mushroom cultivation is discussed.

A pluralistic approach in the study of Pleurotus species with emphasis on compatibility and physiology of the European morphotaxa

The anatomical, physiological, ecological and cultural characters of 11 Pleurotus morphotaxa reported to occur in Europe are described in detail and compared with the outcome of a pairing-analysis performed among monokaryons of 101 dikaryotic strains (including collections from other continents). The results revealed eight intersterility groups in Europe: P. ostreatus, P. pulmonarius, P. cornucopiae, P. eryngii, P. cystidiosus, P. dryinus, P. calyptratus and P. opuntiae . In addition, strains formerly identified as ‘P. sajor-caju’ were found to be intercompatible with P. pulmonarius , while the speciation process currently under way for P. columbinus, P. citrinopileatus and the ecotypes of P. eryngii is discussed. A synthesis of the data obtained so far on Pleurotus systematics is evaluated in the light of recent evidence together with the world distribution of the recognized biological species of the genus.

Decolorization of olive oil mill liquid wastes by chemical and biological means

Abstract The removal of colour from olive mill wastewaters (OMW) using aluminium sulphate [Al2(SO4)3·18H2O], lime (CaO) and hydrogen peroxide (H2O2) was investigated, along with the decolorizing effect of sixteen strains of Pleurotus. In general terms all chemical substances exerted a clear decolorizing effect, yet the most effective was hydrogen peroxide, followed by lime and alumina. The tests with Pleurotus isolates were carried out on plates using different concentrations (25%, 50%, 75%, 100%) of sterilized OMW solidified with 1.5% agar. For all strains tested, decolorization proceeded more slowly than radial growth. Among the six Pleurotus species P. cornucopiae (ATCC 38547) and P. ostreatus (ATCC 34675) were the most efficient.

Genetic variability and systematics of eleven Pleurotus species based on isozyme analysis

Eleven enzyme activities were used to study the intraspecific diversity and interspecific relatedness of 11 Pleurotus species: P. abalonus, P. columbinus, P. cornucopiae, P. cystidiosus, P. dryinus, P. eryngii, P. flabellatus, P. ostreatus, P. pulmonarius, P. sajor-caju, and P. sapidus. In addition, the zymograms of their homokaryotic progenies were evaluated to determine the number of genes and alleles encoding them. Among the 18 loci detected, three coded for PEP A, two for G6PD, LAP, MDH, PEP C and PGM, and one for APH, HK, IDH, 6PGD and PHI. Based on electrophoretic patterns, the 77 wild Pleurotus dikaryons were divided into 51 genotypic classes. The higher intraspecific genetic variation was demonstrated by P. cystidiosus and P. eryngii, while P. cornucopiae, P. dryinus and P. sajor-caju appeared to be the least diverse species examined. Furthermore, with the aid of numerical analysis, valid species such as P. cornucopiae, P. dryinus, P. eryngii and P. flabellatus were clearly distinguished. Among the rest of the taxa studied, the derived dendrograms permitted the delimitation between P. abalonus-P. cystidiosus and P. columbinus-P. ostreatus, although the former members of these two pairs were previously considered as varieties. On the other hand P. pulmonarius and P. sajor-caju formed a tight cluster indicative of a certain genetic affinity, which questions their original designation as distinct species. As regards P. sapidus, it presented a slightly higher proximity to the P. pulmonarius-P. sajor-caju complex than to P. ostreatus. Finally, the phylogenetic implications from the findings of this work are discussed.

Olive mill waste as a substrate for nitrogen fixation

Abstract Olive mill wastewaters (OMWW) because of their low content in nitrogenous organic components and reachness in carbon sources offer a highly favourable environment for the growth of free-living dinitrogen fixing microorganisms. This property is manifested both in natural environments and in axenic cultures. Repetitive addition of OMWW to soil under aerobic conditions leads progressively to its enrichment with dinitrogen fixers, the activity of which is beneficial to soil fertility. The microbial consortium that develops in soil is dominated mostly by members of Azotobacter. A very efficient N2-fixing and slime producing strain of Azotobacter vinelandii (strain A) was isolated from such an enriched soil sample. The isolate is deposited in the culture collection of our laboratory and its biochemical and molecular characteristics are investigated. The strain proved to be effective in bio-remediation processes of OMWW both in a laboratory-scale fermenter unit and a field pilot plant of ca 5 m3 capacity. The inhibitory growth-limiting components of the principal OMWW constituents and their impact on the duration of the lag period of N2-fixing activity recovery is examined. The design of a multi-stream two stage process is described which provides a stable N2-fixing system suitable for the bio-transformation of OMWW into an agrobiological product and/or for the production of extracellular polysaccharide ‘slime’ in high yields.

Bio-fertilization of olive oil mills liquid wastes. The pilot plant in Messinia, Greece

Abstract A method for the biological processing of olive mills liquid wastes (OMWW) for the preparation of a product suitable for agricultural use is described. This method exploits OMWW as a substrate for the cultivation of dinitrogen-fixing microorganisms (Azotobacter vinelandii) capable of transforming the material into an organic liquid of high fertilizing and soil conditioning value. The results which have been obtained from the application of this bio-fertilizer for the culture of olive trees, vines and potatoes was very promising.

First record of the natural occurrence in Europe of the basidiomycete Pleurotus cystidiosus on a new host

The occurrence of the edible basidiomycete Pleurotus cystidiosus is reported for the first time in the European continent. It was isolated along with its synnematal anamorph Antromycopsis broussonetiae in the Pireus prefecture, Greece, from the trunk of a fig-tree ( Ficus carica ), which represents a new host for this species. The morphological characteristics and some physiological features of the fungus are described. The differences between this isolate and the related taxa of P. abalonus, P. smithii and P. gemmellarii are outlined, and the significance of the new record is discussed.