Curtin PhD scholarship opportunity (Aus/NZ residents only)

2023 RTP - Dissecting the functions of a quorum-sensing controlled network of non-coding RNAs in the genus Mesorhizobium

Applications close: 18/08/2022

Mesorhizobium spp. are soil bacteria capable of forming a range of nitrogen-fixing symbioses with agriculturally important legumes. In Australia and New Zealand, high performing Mesorhizobium spp. strains are selected for use as agricultural inoculants for chickpea and clover, providing an economically and environmentally-friendly alternative to chemical fertilisation. However, the benefits of introduced inoculants can be short-lived in Australian soils as introduced strains are outcompeted by native Mesorhizobium spp., which lack the genetic capacity for symbiosis. Therefore, development of Mesorhizobium spp. strains that are competitive with indigenous species would be agriculturally beneficial. We have discovered a distinct quorum-sensing system (MQS) conserved in the genus Mesorhizobium, which allows Mesorhizobium spp. to communicate specifically with each other through the secretion and response to a novel signalling molecule (5Z)-N-[(3S)-2-Oxotetrahydro-3-furanyl]-5-dodecenamide (5-cis-C12-HSL). Despite the ubiquitous presence of the MQS locus in the genus, the cellular functions controlled by MQS are unclear. Intriguingly, strains deleted for the MQS system initially outcompete wild-type strains in co-culture experiments but the wild-type strain ultimately prevails in nutrient-limited stationary-phase conditions. RNA sequencing of MQS mutant strains led to the discovery that the primary output of the MQS system is to activate transcription five novel non-coding RNA (ncRNA) genes, which are also highly conserved throughout the genus. The proximity of ncRNA genes and the MQS locus with genes involved in phosphate uptake, storage and metabolism suggests they may control phosphate utilisation. Australian soils are deficient in phosphorus, so understanding how introduced legume symbionts manage and utilise phosphate may provide additional avenues for inoculant improvement. This project will explore the molecular functions of the ncRNA genes and test the hypothesis that these ncRNA are involved in phosphate metabolism.

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