From agro-industrial wastes to single cell oils: a step towards prospective biorefinery

Abstract

The reserves of fossil-based fuels, which currently seem sufficient to meet the global demands, is inevitably on the verge of exhaustion. Contemporary raw material for alternate fuel like biodiesel is usually edible plant commodity oils, whose increasing public consumption rate raises the need of finding a non-edible and fungible alternate oil source. In this quest, single cell oils (SCO) from oleaginous yeasts and fungi can provide a sustainable alternate of not only functional but also valuable (polyunsaturated fatty acids (PUFA)-rich) lipids. Researches are been increasingly driven towards increasing the SCO yield in order to realize its commercial importance. However, bulk requirement of expensive synthetic carbon substrate, which inflates the overall SCO production cost, is the major limitation towards complete acceptance of this technology. Even though substrate cost minimization could make the SCO production profitable is uncertain, it is still essential to identify suitable cheap and abundant substrates in an attempt to potentially reduce the overall process economy. One of the most sought-after in-expensive carbon reservoirs, agro-industrial wastes, can be an attractive replacement to expensive synthetic carbon substrates in this regard. The present review assess these possibilities referring to the current experimental investigations on oleaginous yeasts, and fungi reported for conversion of agro-industrial feedstocks into triacylglycerols (TAGs) and PUFA-rich lipids. Multiple associated factors regulating lipid accumulation utilizing such substrates and impeding challenges has been analyzed. The review infers that production of bulk oil in combination to high-value fatty acids, co-production strategies for SCO and different microbial metabolites, and reutilization and value addition to spent wastes could possibly leverage the high operating costs and help in commencing a successful biorefinery. Rigorous research is nevertheless required whether it is PUFA-rich oil production (for competing with algal omega oils) or neutral bulk oil production (for overcoming yield limitations and managing process economy) to establish this potential source as future resource.

Comprehending the influence of critical cultivation parameters on the oleaginous behaviour of potent rotten fruit yeast isolates

“…), lipids and industrial and municipal organic wastes (Diwan et al . ). Glucose is generally referred as a readily utilizable form of carbon for microbial growth and metabolism; however, different microbial species respond differently to different carbon sources in any bioprocess.…”

“…On the other hand, exhaustion of intracellular nitrogen provokes the cleavage of AMP: adenosine monophosphate via AMP‐desaminase to IMP: inosine monophosphate and NH 4 + for supplementing the cellular nitrogen deficiency (Diwan et al . ). This leads to rapid decline in cellular AMP concentration, causing alteration and consequentially decline in activity of crucial enzyme of Krebs cycle, AMP dependent‐NAD + isocitrate dehydrogenase, responsible for transforming isocitric to a‐ketoglutaric acid.…”

“…Under these circumstances, a non‐oleaginous microorganism either secrete out this intracellularly accumulated citrate or drive excess carbon pool to polysaccharide synthesis (Diwan et al . ). However, oleaginous organisms during such starvation channelize the intracellular citrate pool toward fatty acid and TAG synthesis by means of a specialized enzyme called ATP: citrate lyase (ACL) (Boulton and Ratledge ), which converts citrate to acetyl‐CoA, the building block in fatty acid synthesis machinery.…”

“…Example of some such oleaginous yeasts and moulds extensively reported to be oleaginous are Mortierella alpina , Mortierella isabellina , Trichosporon cutaneum , Trichosporon fermentans, Rhodotorula graminis , Rhodotorula glutinis, Cryptococcus curvatus, Yarrowia lipolytica, Lipomyces starkeyi, Rhodosporidium toruloides, Mucor circinelloides (Diwan et al . ), and yet there are several scattered in nature to be isolated and harnessed. Addition of new isolates to the pool of such existing ones, will expand the alternatives of suitable oleaginous candidates for desired applications.…”

Volatile fatty acids as novel building blocks for oil‐based chemistry via oleaginous yeast fermentation

“…Yeasts have the outstanding capability to be cultivated on a wide range of wastes, such as sugar-based materials (lignocellulosic residues), glycerol, and hydrophobic substrates (HS; crude oil, industrial fatty acids, and so forth; Diwan et al, 2018b;Papanikolaou & Aggelis, 2011a). Therefore, the utilization of organic wastes for lipid production by oleaginous yeasts (OYs) can be considered as a cost-effective technology to partially replace petroleum in oil-based chemistry within the so-called circular bioeconomy.…”