Tolerance and elimination of oxolic acid by Trichoderma spp.

Abstract:

[Objective] Oxalic acid (OA) is a virulence factor of several plant pathogens, e.g. Sclerotinia sclerotiorum and Botrytis cinerea. Some strains of Trichoderma spp. have the ability to eliminate OA and thereby reduce disease incidence, while the pathways and mechanism of OA elimination have not been well discovered. [Methods] In this study, T. harzianum LTR-2, performed the best capacity of OA elimination among 42 Trichoderma strains under the stress of 30 mmol/L OA. The developmental features of LTR-2 under OA stresses were analyzed using morphology and in situ observational methods. OA elimination rates, ambient pH and biomass under different OA stresses were analyzed. Then, the growing states of LTR-2 were described under the condition of OA as the sole carbon source. In the end, Real-time PCR was used to analyze expression level of OXDC coding gene LTR_4445. [Results] LTR-2 was cultured on PDA plate containing different concentrations of OA. With 50?80 mmol/L of OA, LTR-2 could survive, but didn’t form normal colon. With 30?50 mmol/L of OA, LTR-2 developed chlamydospores firstly, which then germinated hypha and formed normal colon. LTR-2 could eliminate OA in liquid culture. LTR-2 showed the highest OA elimination rate of 66.50% under 20 mmol/L OA, and the second highest of 55.06% under 10 mmol/L. When OA concentration was enhanced to 50?80 mmol/L, the OA elimination rate was dropped down to 6.75%?38.94%. pH of culture filtrate was enhanced to varying extents along with OA elimination under different OA stresses, and the highest increase occurred under the concentration of 10 and 20 mmol/L. Interestingly, OA showed growth-promoting effect when concentration was under 20 mmol/L. Moreover, LTR-2 could develop macroscopic mycelium pellet when OA (<20 mmol/L) was the sole carbon source in media. Transcriptional level of LTR_4445 was up-regulated under OA stress. [Conclusion] Our study implied that Trichoderma spp. may employ several strategies under OA stress besides degradation, e.g. transformation on stress-resistance mode, converting OA into a precursor of nutrients, etc.

Key words:Trichoderma harzianum LTR-2, OA tolerating, Developmental pattern, OA elimination