Microbial community dynamics and their impact on plant performance under phosphorous limiting condition

MSc Claudia Probst

4/2023

Supervision: Dr. Delphine Chinchilla, Prof. Klaus Schlaeppi

Abstract:

Nowadays, farmers face numerous challenges in meeting the high demand for crops while ensuring food security and sustainably preserving the environment. The availability of phosphorous (P) in the soil is often limited due to the fixation of P into complex compounds. Root-associated microorganisms, in particular phosphate solubilizing bacteria (PSB) are widely investigated for their potential to enhance crop productivity in a sustainable way, by converting inorganic P into plant-available P.

In this master’s project, we aimed to reproduce and further study the microbe-induced growth effect in A. thaliana under P-limiting conditions, as previously observed by Dr. Delphine Chinchilla. This approach involved the use of a synthetic community consisting of nine bacterial strains (SynCom9). We investigated whether plants were subjected to low P conditions and whether this response led to the activation of the phosphate starvation response (PSR) by evaluating the expression levels of a PSR marker gene (AT4), which is known to be induced under P-stress. We identified PSB strains among SynCom9 that are capable to solubilize inorganic P. Furthermore, we examined the composition of the microbial community by 16S rRNA sequencing in response to varying levels of P and we investigated whether the identified PSB are specifically recruited under P-stress.

Our findings provide evidence that SynCom9 positively influences the growth of A. thaliana under P-stress, supporting the findings from Dr. Delphine Chinchilla. The qPCR results suggest that plants are subjected to P-stress when grown under low P conditions. Under these conditions, plants induce the PSR, which is further enhanced in presence of microbes. Although we identified three strains from the SynCom9 as effective PSBs, the abundance of these strains remained unaltered under P-limiting conditions, indicating that PSB were not recruited to mitigate the effects of P-stress. The specific mechanisms that contributed to the growth promoting effect in A. thaliana by SynCom9 warrants further studies. While it is possible that Pseudomonas strains contributed to an enhance growth by solubilizing inorganic P, these strains were not specifically recruited under P-stress. Therefore, it is likely that other mechanisms are involved.