Abstract
Tetrahydrofuran (THF) is a universal solvent widely used in the synthesis of chemicals and pharmaceuticals. As a refractory organic contaminant, it can only be degraded by a small group of microbes. In this study, a thiamine auxotrophic THF-degrading bacterium, Rhodococcus ruber ZM07, was isolated from an enrichment culture H-1. It was cocultured with Escherichia coli K12 (which cannot degrade THF but can produce thiamine) and/or Escherichia coli K12ΔthiE (which can neither degrade THF nor produce thiamine) with or without exogenous thiamine. This study aims to understand the interaction mechanisms between ZM07 and K12. We found that K12 accounted for 30% of the total when cocultured and transferred with ZM07 in thiamine-free systems; in addition, in the three-strain (ZM07, K12, and K12ΔthiE) cocultured system without thiamine, K12ΔthiE disappeared in the 8th transfer, while K12 could still stably exist (the relative abundance remained at approximately 30%). The growth of K12 was significantly inhibited in the thiamine-rich system. Its proportion was almost below 4% after the fourth transfer in both the two-strain (ZM07 and K12) and three-strain (ZM07, K12, and K12ΔthiE) systems; K12ΔthiE’s percentage was higher than K12’s in the three-strain (ZM07, K12, and K12ΔthiE) cocultured system with exogenous thiamine, and both represented only a small proportion (less than 1% by the fourth transfer). The results of the coculture of K12 and K12ΔthiE in thiamine-free medium indicated that intraspecific competition between them may be one of the main reasons for the extinction of K12ΔthiE in the three-strain (ZM07, K12, and K12ΔthiE) system without exogenous thiamine. Furthermore, we found that ZM07 could cooperate with K12 through extracellular metabolites exchanges without physical contact. This study provides novel insight into how microbes cooperate and compete with one another during THF degradation.
Highlights
As an important solvent, tetrahydrofuran (THF) is widely applied in the chemical industry
We speculated that intracellular thiamine, which may still remain during the first transfer, supported the growth of strain ZM07 in the starting phase
The results showed that strain ZM07 could grow and degrade THF normally when cocultured and transferred with K12 wild type (Supplementary Figure S3D), while it could not restore its growth and THF degradation ability when cocultured with K12 thiE (Supplementary Figure S3E)
Summary
Tetrahydrofuran (THF) is widely applied in the chemical industry. One of the most widely accepted THF metabolic pathways is the oxidation pathway, whereby THF is initially oxidized into 2-hydroxytetrahydrofuran (2-OH THF), which can form γ-butyrolactone or γ-hydroxybutyraldehyde Both of these compounds can form γ-hydroxybutyrate, which can be further oxidized to succinate and enter the tricarboxylic acid cycle (Bernhardt and Diekmann, 1991; Thiemer et al, 2003; Morenohorn et al, 2005; Tajima et al, 2012). Previous studies found that a number of microorganisms are auxotrophic in nature and rely on external nutrients (i.e., amino acids, vitamins and other cofactors) for growth (D’Souza et al, 2014; Wexler and Goodman, 2017; Liu et al, 2018). The question remains as to how auxotrophic microorganisms, especially contaminant-degrading bacteria, perform their functions in microbial communities
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