Uprising fossil fuel depletion and deterioration of ecological reserves supply have led to the search for alternative renewable and sustainable energy sources and chemicals. Although first generation biorefinery is quite successful commercially in generating bulk of biofuels globally, the food versus fuel debate has necessitated the use of non-edible feedstocks, majorly waste biomass, for second generation production of biofuels and chemicals. A diverse class of microbes and enzymes are being exploited for biofuels production for a series of treatment process, however, the conversion efficiency of wide range of lignocellulosic biomass (LCB) and consolidated way of processing remains challenging. There were lot of research efforts in the past decade to scour for potential microbial candidate. In this context, evolution has developed the gut microbiota of several insects and ruminants that are potential LCB degraders host eco-system to overcome its host nutritional constraints, where LCB processed by microbiomes pretends to be a promising candidate. Synergistic microbial symbionts could make a significant contribution towards recycling the renewable carbon from distinctly abundant recalcitrant LCB. Several studies have assessed the bioprospection of innumerable gut symbionts and their lignocellulolytic enzymes for LCB degradation. Though, some reviews exist on molecular characterization of gut microbes, but none of them has enlightened the microbial community design coupled with various LCB valorization which intensifies the microbial diversity in biofuels application. This review provides a deep insight into the significant breakthroughs attained in enrichment strategy of gut microbial community and its molecular characterization techniques which aids in understanding the holistic microbial community dynamics. Special emphasis is placed on gut microbial role in LCB depolymerization strategies to lignocellulolytic enzymes production and its functional metagenomic data mining eventually generating the sugar platform for biofuels and renewable chemicals production.

In this study we employed microwave-acid pretreatment for water hyacinth (WH) to obtain liquid hydrolysate that contains sugars derived from holocellulosic components of biomass for further oleaginous yeast fermentation. In order to remove the inhibitors such as furans after acid treatment, detoxification of hydrolysate was done and we compared the efficiency of this step with non-detoxified hydrolysate towards capability of the Rhodosporidium toruloides NCIM 3547 (an oleaginous yeast) to produce microbial lipid and single cell protein. The results indicated that the reducing sugar concentration was found to be higher in non-detoxified hydrolysate (65.41 g/L) than detoxified one (59.18 g/L).When the non-detoxified liquid hydrolysate was supplemented with yeast extract as a complex organic source for R. toruloides, resulted in a maximum lipid yield of about 0.813 ± 0.041 (g/g) and 53.60 ± 2.68 (g/g) of single cell protein content with 0.038 g/L/d of protein productivity. Two kinetic models, hybrid Logistic-Monod and Luedeking-Piret were employed to assess the microbial growth and the substrate utilization and were found to be in well agreement with the experimental data with a coefficient of determination (R 2 ) value ranging from 0.95 -0.99 thereby demonstrating the efficiency of the hydrolysate supplemented media. Further, GC-MS analysis of transesterified lipids revealed the presence of various FAME (fatty acid methyl esters) and also the presence of increased levels of total saturated fatty acids (35.03%) advocates its high potential in biodiesel production. This study demonstrates the feasibility of sustainable valorization of WH derived liquid hydrolysate towards a greener biorefinery framework.

Allelopathy, a complex phenomenon has unveiled both stimulatory and inhibitory effects in plant processes that are mediated by the release of certain chemical compounds commonly known as allelochemicals. Allelochemicals, a form of bioactive secondary metabolites are produced by a diverse group of plants and microbes in response to biotic and abiotic stress. It ranges from a simple hydrocarbon to complex polycyclic aromatic compounds like phenol, flavonoids, tannins, steroids, amino acids, alkaloids and quinones. These plant bioactive compounds are released into the environment via decomposition, exudation, leaching and volatilization that play a significant role in regulating the intra-specific or inter-specific relations with counterparts. A wide variety of methods has been proposed for analyzing the basic mechanism and overall effect of allelochemicals. However, the lack of a reliable and effective method to identify their molecular mode of action and their modulation in the metabolic pathway still remains as a great challenge. From a commercial perspective, these allelochemicals are deemed to be better candidates for green natural herbicides and weedicides that are proven to be environment friendly, unlike synthetic chemicals. In order to pave a way for the economic viability of these chemicals, a basic understanding of their chemistry is inevitable. This review article is focused to give an in-depth understanding of metabolic pathways genes responsible for the elicitation/secretion and the adoption of a suitable downstream process and analytical techniques that can intensify the process.

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To overcome the obstacles of treatment of dairy wastewater (DW) under anaerobic mono‐digestion and sustainable disposal of harvested water hyacinth (WH) a novel sequential valorization strategy was adopted to obtain fuel and fertilizer. Initially, DW and WH were subjected for anaerobic co‐digestion to elucidate the synergistic effect of the substrates to improve the process efficiency and increased biomethane production. The results indicated that the co‐digestion mixture (DW: WH‐1:1) has resulted in biomethane yield of 504.38 L/Kg VSfed which is 1.28‐fold and 3.14‐fold higher as compared to the mono‐digestion of WH (431.71 L/Kg VSfed) and DW (160.59 L/Kg VSfed), respectively. Further, the residual digestate was subjected for slow pyrolysis (320 ± 15°C) to obtain bio‐oil and biochar. The obtained bio‐oil shown superior fuel characteristics as compared to direct WH bio‐oil resulting in density, viscosity, and calorific value of 1.21 ± 0.04 g/ml, 1.8 ± 0.05 cSt and 1766.82 ± 11.53 KJ/Kg, respectively. The biochar residue from pyrolysis was amended to the soil to determine its bio‐fertilizing property. The soil properties in terms of bulk density, porosity, organic carbon, and pH were enhanced. Tomato cultivation in biochar amended soil shown comparable vegetative growth to that of digestate and urea thereby advocating the replacement of chemical fertilizers. Practical Application With recent increase in environmental concerns and requirement to meet the prescribed limits for effluent discharge from the industries, especially from food processing for the protection of aquatic bodies, there is a requirement of adoption of cost effective technology that could provide both economic and ecological sustainability. In this study, a sequential valorization strategy was adopted for efficient management of dairy wastewater and harvested water hyacinth from the water resources. The resultant products biogas, bio‐oil and biochar could be potentially used as fuel and fertilizer. Circular bio‐economy is in need of time which could be attainable by the implementation of such strategies in large scale industries for efficient waste management and resource recovery. This will not only benefit the environment but also to the society by galvanizing the sustainable development technology.