Bioconversion of D-limonene into value-added monoterpenes using Paenibacillus popilliae 1C and Streptomyces rochei AB1: Exploring bacterial biotransformation pathways and metabolite diversity

Abstract

The present study focuses on the bioconversion of D-limonene using two bacterial strains, Streptomyces rochei AB1 and Paenibacillus popilliae 1C, isolated and identified by our research team. Rich mediums (International Streptomyces Project 9 medium for strain AB1 and Luria–Bertani medium for strain 1C) were used for biotransformation experiments. Furthermore, biodegradation tests were conducted with D-limonene as the only carbon and energy source in a modified minimum medium. The minimum inhibitory concentration (MIC) of D-limonene was 10±0.09 mg/mL. The strains achieved a bioconversion yield of nearly 70% following 7-day of incubation period. Analysis by GC-MS revealed the formation of various hydrocarbons and oxygenated monoterpenes, including alcohols, ketones and terpene hydrocarbons. Some metabolites, such as cis-verbenol, isovaleric acid and 2-methylbutanoic acid, were identified in biotransformation assays using Paenibacillus popilliae 1C. To our knowledge, this genus has never before been known to produce these metabolites during the biotransformation of D-limonene. Carveol, carvone, limonene-1,2-diol, linalool, and α-terpinolene were among the other metabolites found. Similar biodegradation products were obtained with Streptomyces rochei AB1, suggesting the occurrence of common metabolic pathways involved in D-limonene bioconversion. These findings highlight the biotechnological potential of the studied strains for the production of value-added monoterpenes.