Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. Οn the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Knowledge of the agricultural soil microbiota, of the microbial consortia that comprise it, and the promotion of agricultural practices that maintain and encourage them, is a promising way to improve soil quality for sustainable agriculture and to provide food security. Although numerous studies have demonstrated the positive effects of beneficial soil microorganisms on crop yields and quality, the use of microbial consortia in agriculture remains low. Microbial consortia have more properties than an individual microbial inoculum, due to the synergy of the microorganisms that populate them. This review describes the main characteristics, ecosystem functions, crop benefits, and biotechnological applications of microbial consortia composed of arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), and Actinobacteria, to promote the restoration of agricultural soils and, consequently, the quality and health of agricultural crops. The aim is to provide knowledge that will contribute to the development of sustainable and sufficiently productive agriculture, which will adapt in a good way to the pace of the growing human population and to climate change.

Conventional agriculture has important challenges to guarantee soil fertility and sustainable food production. Many agricultural soils in the world are degraded and multiple strategies are currently being developed to restore them. The study of beneficial soil microorganisms has attracted increasing interest due to their relevant role in sustainable agricultural development. The balance and maintenance of ecosystem services, such as biomass transformation, nutrient cycling, plant growth, and health, are directly dependent on soil microbial activity. Therefore, it is important to promote its establishment and propagation. An ancient technique that favors soil biodiversity is the production and application of compost. While numerous studies have focused on the benefits of plant cultivation, fewer studies have focused on the benefits for soil microbiota. The objective of this review was to elucidate the role of the microbiota in the composting process and its impact on soil microorganisms in agriculture. The review presents the advances in the knowledge and importance of microorganisms involved in the composting process and how compost promotes the maintenance and multiplication of beneficial microbial consortia and their ecosystem functions in agricultural soils, shifting towards a more sustainable and resilient agriculture.

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Knowledge of the agricultural soil microbiota, of the microbial consortia that comprise it, and the promotion of agricultural practices that maintain and encourage them, is a promising way to improve soil quality for sustainable agriculture and to provide food security. Although numerous studies have demonstrated the positive effects of beneficial soil microorganisms on crop yields and quality, the use of microbial consortia in agriculture remains low. Microbial consortia have more properties than an individual microbial inoculum, due to the synergy of the microorganisms that make them up. This review describes the main characteristics, ecosystem functions, crop benefits and biotechnological applications of microbial consortia composed of arbuscular mycorrhizal fungi, plant growth promoting bacteria and actinobacteria, to promote the restoration of agricultural soils and, consequently, the quality and health of agricultural crops. The aim is to provide knowledge that will contribute to the development of sustainable and sufficiently productive agriculture, which will adapt in a good way to the pace of the growing human population and to climate change.

Pomegranate residues (PRs) (i.e. the solid residues remaining after juice extraction), generated currently in abundance in Greece, contain a variety of carbon sources and therefore can be regarded as a potential feedstock for chemical and biotechnological processes rather than as waste materials. In the current project, the polysaccharides contained in PRs were extracted and hydrolyzed in a one-step process without the use of chemical reagents and the resulting broth was used as substrate in biotechnological applications, including ethanol and single cell oil (SCO) production. The yeasts Meyerozyma guilliermondii, Scheffersomyces coipomoensis, Sugiyamaella paludigena and especially Saccharomyces cerevisiae, were able to efficiently convert PR derived reducing sugars into bioethanol. Ethanol production under anaerobic conditions ranged from 3.6 to 12.5 g/L. In addition, the oleaginous yeasts Lipomyces lipofer and Yarrowia lipolytica as well as M. guilliermondii, S. coipomoensis and S. paludigena were tested for their ability to accumulate lipids suitable as feedstock for biodiesel production. Lipids were accumulated at concentrations up to 18% and were rich in palmitic acid (C16:0) and oleic acid (C18:1). Finally, the oleaginous fungus Cunnichamella echinulata was cultivated on PR based solid substrates for γ-linolenic acid (GLA) production. The fermented bio-products (i.e. fermented substrate plus fungal mycelia) contained up to 4.8 mg GLA/g of dry weight. Phenolic removal (up to 30%) was achieved by several of the above mentioned microorganisms, including C. echinulata, L. lipofer, M. guilliermondii, S. paludigena and Y. lipolytica. We conclude that PRs can be used as a raw material for microbial growth, ethanol and SCO production, which is of economic and environmental importance.

The application of organic amendments is an increasingly widespread practice, which allows fertilizing and restoring soils in a sustainable and environmentally friendly way. Improving the quality of amendments through the application of microorganisms has been a challenge in recent years. The objective of the study was to determine the effects of microalgae+compost (1:1) mixture on the yield of cauliflower (Brassica oleracea L. var. botrytis L.) plants grown in a sandy loam soil with low nutrient availability. Yields were compared with the application of compost, cattle manure and two chemical fertilizers. The treatments applied were: T1 prepared with urea (NPK 46-0-0), triple superphosphate (NPK 0-46-0) and potassium saltpeter (NPK 15-0-14); T2 commercial fertilizer (NPK 12-11-18); T3 microalgae biomass (T3); T4 compost; T5 1:1 microalgae+compost mixture; T6 cattle manure; and T0 control (no fertilization). The experiments were conducted in 30 L pots using 40 g soil per plant and 4 g N as a reference to standardize fertilizer application. The results showed that the fresh weight (FW) and dry weight (%DW) of T5 and T6 were not significantly different from those of T1 (p > 0.05), on the contrary, FW of T5 and T6 was 43.8% and 40% higher than in T2, as well as the %DW was 0.59% and 0.6% w w -1 , also higher than in T2. These results suggest that the microalgae+compost mixture is an alternative fertilizer, equivalent to chemical fertilizers and manure, presenting the advantages of being more stable, sustainable, and environmentally friendly. However, further studies are needed to determine the necessary dose per cultivated plant species.

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