Summary Sustainable economic and industrial growth is the need of the hour and it requires renewable energy resources having better performance and compatibility with existing fuel infrastructure from biological routes. Isoprenoids (C ≥ 5) can be a potential alternative due to their diverse nature and physiochemical properties similar to that of petroleum based fuels. In the past decade, extensive research has been done to utilize metabolic engineering strategies in micro‐organisms primarily, (i) to overcome the limitations associated with their natural and non‐natural production and (ii) to develop commercially competent microbial strain for isoprenoid‐based biofuel production. This review briefly describes the engineered isoprenoid biosynthetic pathways in well‐characterized microbial systems for the production of several isoprenoid‐based biofuels and fuel precursors.

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Aging, the major cause of several ailments has led to intense exploration of potential drugs that delay aging and its associated effects. We mined the information on traditional Indian medicines and identified an iridoid, 10-O-trans-p-Coumaroylcatalpol (OCC), a major ingredient of Premna integrifolia Linn. (syn: Premna serratifolia). OCC forms an important constituent of famous herbal formulation 'Dashmula', a ten herb formulation, commonly used for its various medicinal properties. Employing model system C. elegans, the effect of OCC on life span, stress resistance, chemotaxis, the content of reactive oxygen species (ROS) and on the aggregation of alpha synuclein was studied. OCC extended the mean life span of nematodes, increased their tolerance against chemical induced stress, improved the chemotaxis index and reduced the ROS content. Further, the aggregation of Parkinson's disease (PD) associated protein, alpha synuclein (asyn), was decreased when transgenic a-syn expressing worms were raised on OCC mixed diet. We extended the studies further to explore the possible genetic mechanism that mediates the observed effects of OCC. Employing the genetic knockout mutants TK22 [mev-1(kn1)III]; GR1307 [daf-16(mgDf50)I]; VC199 [sir-2.1(ok434)IV] and transgenic GFP expressing strain TJ356 [zls356; DAF-16::GFP], our studies revealed that the effects were mediated by daf-16 and not by sir-2.1 or mev-1. Our results indicate that OCC has the ability to ameliorate a-syn aggregation, reduce oxidative stress and promote longevity in C. elegans via activation of longevity promoting transcription factor DAF-16. Thus, OCC may serve as a lead compound of plant origin for important nutraceutical intervention against aging and age associated PD.

bEnthusiasm for mining advanced biofuels from microbial hosts has increased remarkably in recent years. Isoprenoids are one of the highly diverse groups of secondary metabolites and are foreseen as an alternative to petroleum-based fuels. Most of the prokaryotes synthesize their isoprenoid backbone via the deoxyxylulose-5-phosphate pathway from glyceraldehyde-3-phosphate and pyruvate, whereas eukaryotes synthesize isoprenoids via the mevalonate pathway from acetyl coenzyme A (acetyl-CoA). Microorganisms do not accumulate isoprenoids in large quantities naturally, which restricts their application for fuel purposes. Various metabolic engineering efforts have been utilized to overcome the limitations associated with their natural and nonnatural production. The introduction of heterologous pathways/genes and overexpression of endogenous/homologous genes have shown a remarkable increase in isoprenoid yield and substrate utilization in microbial hosts. Such modifications in the hosts' genomes have enabled researchers to develop commercially competent microbial strains for isoprenoid-based biofuel production utilizing a vast array of substrates. The present minireview briefly discusses the recent advancement in metabolic engineering efforts in prokaryotic hosts for the production of isoprenoid-based biofuels, with an emphasis on endogenous, homologous, and heterologous expression strategies.

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