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THEME-1: Biotransformation of plant phenylpropanoids

The main aim of this theme was to evaluate the capabilities of various fungal and actinomycetes isolates for carrying out the degradation (chain-shortening) of various hydroxycinnamic acids (C6-C3) into C6-C1 compounds such as p-hydroxybenzoic acid, vanillin, syringic acid and other C6-C3 compounds, such as, caffeic acid. Agro-industrial wastes, such as wheat bran, rice bran, sugarcane bagasse are rich sources of natural ferulic acid (a hydroxycinnamic acid). We collaborated with Prof Sukanta K Sen of Visva-Bharati University and obtained a joint funding from DBT to pursue further. The goal of the DBT-funded project was to release the wall-bound ferulic acid (either chemically and/or enzymatically) and to convert this phenolic acid to vanillin and vanillic acid through microbial biotransformation. We explored and assessed the capabilities of antibiotic-producing Streptomyces species to carry out this biotransformation.

Findings 1
We demonstrated stable accumulation of vanillic acid as such in the spent medium of Streptomyces for the first time, upon transformation of ferulic acid. Catabolic route of ferulate degradation with this species and detailed in vitro conversions were also established. Supplementation experiment with a plant 4-CL enzyme inhibitor suggested a CoA-dependent phenylpropanoid side-chain cleavage route was in operation towards the formation of vanillin and vanillic acid from ferulic acid.

Findings 2
Simultaneous formation of caffeic acid and 4-hydroxybenzoic acid by a soil actinomycetes species (identified as Streptomyces caeruleus) upon biotransformation of 4-coumaric acid was demonstrated for the first time. The ability to induce plant phenolic pathway in this species suggests the possibility of origin of some “typical plant pathways” from microorganisms, particularly from actinomycetes group because of their proximity to plants in the soil environment. We have further characterized the late enzymes of these biotransformations.

Findings 3
We isolated a filamentous fungus (identified as Paecilomyces variotii MTCC 6581) from cell wall wastes and demonstrated the capability of this microorganism to convert different hydroxycinnamic acids into their respective C2 chain-cleavage products such as vanillic acid, 4-hydroxybenzoic acid and syringic acid. However, when cinnamic acid was used as sole carbon source, the microorganism produced cinnamyl alcohol (a C6-C3 compound) along with benzoic acid (a C6-C1 compound).  When eugenol was used as sole carbon source, coniferaldehyde and ferulic acid were identified as major biotransformed products. 


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