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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Biogas is composed of CH4 (50-60%) and CO2 (40-50%), therefore scrubbing (removal) of CO2 from biogas is imperative as high concentration of it reduces the calorific value and limits its end application. Problems associated with physiochemical process can be alleviated through microalgae as they are efficient in utilizing the CO2 as its carbon source that can be technically termed as CO2 sequestration. This study aims to apply the use of a microalgae CO2 capturing system using Chlorella sorokiniana and Scenedesmus obliquus that have higher photosynthetic capacity and sequestration of carbon dioxide subsequently and transforming into biomass. Chlorella sorokiniana had a total biomass yield of 1.59 g/L and 1.98 g/L for unpurged and purged respectively. Scenedesmus obliquus on the other had a better yield over Chlorella sorokiniana with an overall biomass of 1.7 g/L for unpurged and 2.4 g/l under mixotrophic condition. Upon analysis of lipid content in the biomass, the cultures that were grown under mixotrophic condition were found to yield 3.45 and 3.28 fold higher as compared to unpurged sample in Chlorella and Scenedesmus respectively. Under purged conditions, Chlorella sorokiniana had the maximum yield of 5.5 mg/g of vitamin E compared to Scenedesmus obliquus with a comparatively lower yield of 2.32 mg/g. Overall, the increase in the specific growth rate and doubling time indicated that a better adaptability and utilization of carbon source in the purged sample which was provided in the form of 50% citric acid and carbon dioxide. This provides evidence in support of Chlorella sorokiniana for having a higher potential in the area of nutraceuticals. Along with purifying the biogas produced from an anaerobic digester fed with food waste.

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