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Background: Oleaginous yeasts can be grown on different carbon sources, including lignocellulosic hydrolysate containing a mixture of glucose and xylose. However, not all yeast strains can utilize both the sugars for lipogenesis. Therefore, in this study, efforts were made to isolate dual sugar-utilizing oleaginous yeasts from different sources. Results: A total of eleven isolates were obtained, which were screened for their ability to utilize various carbohydrates for lipogenesis. One promising yeast isolate Trichosporon mycotoxinivorans S2 was selected based on its capability to use a mixture of glucose and xylose and produce 44.86 ± 4.03% lipids, as well as its tolerance to fermentation inhibitors. In order to identify an inexpensive source of sugars, nondetoxified paddy straw hydrolysate (saccharified with cellulase), supplemented with 0.05% yeast extract, 0.18% peptone, and 0.04% MgSO4 was used for growth of the yeast, resulting in a yield of 5.17 g L−1 lipids with conversion productivity of 0.06 g L−1 h−1. Optimization of the levels of yeast extract, peptone, and MgSO4 for maximizing lipid production using Box–Behnken design led to an increase in lipid yield by 41.59%. FAME analysis of single cell oil revealed oleic acid (30.84%), palmitic acid (18.28%), and stearic acid (17.64%) as the major fatty acids. Conclusion: The fatty acid profile illustrates the potential of T. mycotoxinivorans S2 to produce single cell oil as a feedstock for biodiesel. Therefore, the present study also indicated the potential of selected yeast to develop a zero-waste process for the complete valorization of paddy straw hydrolysate without detoxification.How to cite: Sagia S, Sharma A, Singh S, et al. Single cell oil production by a novel yeast Trichosporon mycotoxinivorans for complete and ecofriendly valorization of paddy straw. Electronic Journal of Biotechnology 2020;44. https://doi.org/10.1016/j.ejbt.2020.01.009. Keywords: Biodiesel, Fatty acids, Lignocellulosic biomass, Lignocellulosic hydrolysate, Lipid production, Lipogenesis, Oleaginous yeast, Paddy straw, Single cell oil, Trichosporon mycotoxinivorans, Yeast

Lactic acid is one of the most commonly used organic acids in various industries due to its versatile applications. To meet the market demand its production by various methods, such as chemically and microbiologically, is gaining significant interest. Chemically synthesized lactic acid (hydrolysis of acetonitrile) is generally a racemic mixture of D- and L-lactic acid which further needs purification for use in pharma and food industries. On the other hand, lactic acid produced by microbial fermentation is in an optically pure form of D- or L-lactic acid and does not require any further purification. Microbes used for lactic acid fermentation, such as bacteria, fungi, yeast, and algae, have the potential to use lignocellulosic biomass, organic agrowaste, kitchen waste, dairy, and petroleum industry waste as a feedstock. Therefore recycling of different organic waste for the production of lactic acid not only resolves the issues of waste management but may also help in reducing the production cost of lactic acid. These microorganisms ferment both pentose and hexose sugars to the desired product by two different pathways, i.e., homolactic and heterolactic fermentation pathways. In the course of these pathways, other than lactic acid there are a few other economically important platform chemicals (acetic acid, ethanol, butanol, etc.) also produced. Different microbes play a specific role at different stages of organic waste recycling to lactic acid. Briefly, lignocellulolytic and different glucoamylases-producing microbes (fungi and bacteria) are the main players in the initial steps of pretreatment and saccharification of biomass. After saccharification, when monomeric or dimeric sugar is released from the biomass, the fermentative lactic acid bacteria converts these sugars to the isomeric form of lactic acid. The obtained lactic acid is purified further by various mechanisms and the pure lactic acid then can be used in pharmaceutical, cosmetic, textile, and food industries.

Cellulose is one of the most significant renewable energy sources present on earth and is also the most abundant biomolecule present in biomass. Hence producing indigenous cellulases for depolymerization of cellulose for use in various bioprocesses, namely biofuel production and commodity biochemical synthesis, is vital for the development of sustainable future biorefineries. Cellulolytic enzymes are a set of several enzymes, produced mainly by microorganisms both fungi and bacteria, that synergistically catalyze degradation of holocellulose-releasing oligosaccharides, cellobiose, and glucose units. Interestingly, cellulases are inducible enzymes, whose regulation is precisely regulated by activation and repression mechanisms. These inducible enzymes are produced only in the presence of complex cellulosic substrates, but repressed when simple sugars are present. The cellulosic substrates can either be pure substrates (cellulose powder) or raw lignocellulosic material. Lignocellulosic biomass, being plentiful as well as inexpensive, is usually the preferred substrate for the production of this enzyme system as compared to the pure substrates. Recent transcriptome profiling and quantitative proteomic approaches also reveal induction of specific proteins in the presence of utilizable lignocellulosic carbon sources by different microorganisms. This chapter discusses various pure and lignocellulosic substrates used for microbial cellulase production by either liquid submerged or solid-state fermentation.

Microorganisms in the rhizosphere mediate the cycling of nutrients, their enhanced mobilisation and facilitate their uptake, leading to increased root growth, biomass and yield of plants. We examined the promise of beneficial cyanobacteria and eubacteria as microbial inoculants, applied singly or in combination as consortia or biofilms, to improve growth and yields of okra. Interrelationships among the microbial activities and the micro/macro nutrient dynamics in soils and okra yield characteristics were assessed along with the changes in the soil microbiome. A significant effect of microbial inoculation on alkaline phosphatase activity was recorded both at the mid-crop and harvest stages. Microbial biomass carbon values were highest due to the Anabaena sp. - Providencia sp. (CR1 + PR3) application. The yield of okra ranged from 444.6–478.4 g−1 plant and a positive correlation (0.69) recorded between yield and root weight. The application of Azotobacter led to the highest root weight and yield. The concentration of Zn at mid-crop stage was 60–70% higher in the Azotobacter sp. and Calothrix sp. inoculated soils, as compared to uninoculated control. Iron concentration in soil was more than 2–3 folds higher than control at the mid-crop stage, especially due to the application of Anabaena-Azotobacter biofilm and Azotobacter sp. Both at the mid-crop and harvest stages, the PCR-DGGE profiles of eubacterial communities were similar among the uninoculated control, the Anabaena sp. - Providencia sp. (CW1 + PW5) and the Anabaena-Azotobacter biofilm treatments. Although the profiles of the Azotobacter, Calothrix and CR1 + PR3 treatments were identical at these stages of growth, the profile of CR1 + PR3 was clearly distinguishable. The performance of the inoculants, particularly Calothrix (T6) and consortium of Anabaena and Providencia (CR1 + PR3; T5), in terms of microbiological and nutrient data, along with generation of distinct PCR-DGGE profiles suggested their superiority and emphasized the utility of combining microbiological and molecular tools in the selection of effective microbial inoculants.