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Title: Two different stable low molecular weight RNA (LMW RNA) profiles within Sinorhizobium meliloti and within Sinorhizobium medicae

item Van Berkum, Peter

Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2008
Publication Date: 2/12/2008
Citation: Del Villar, M., Rivas, R., Peix, A., Mateos, P.F., Martinez-Molina, E., Van Berkum, P.B., Willems, A., Velazquez, E. 2008. Two different stable low molecular weight RNA (LMW RNA) profiles within Sinorhizobium meliloti and within Sinorhizobium medicae. FEMS Microbiology Letters. 282:273-281.

Interpretive Summary: The element most limiting agriculture is nitrogen. Farmers provide nitrogen with fertilizer, but a serious problem is that this is not a green practice, is expensive and causes widespread pollution. An environment-friendly approach to provide crops with nitrogen is to grow legumes, which benefit from a symbiosis with bacteria called rhizobia. The rhizobia can provide the growing legume crop with all the necessary nitrogen without applying any fertilizer. However, to achieve this the farmer needs to manage the symbiosis very carefully by combining the specific crop with the appropriate cultures of rhizobia. None of the US major legume crop plants originated in the Americas and so to provide the farmer with the appropriate rhizobia they need to be cultured from foreign soils and brought to the US. The difficulty is how to select among the many different cultures that exist naturally in the soils where our legume crops occur naturally. To address this problem many sophisticated methods based on analysis of the genomes of rhizobia are in development. In this communication we distinguished differences in small biological molecules called RNA among cultures representing two rhizobial species inhabiting Spanish soils that form symbioses with alfalfa and related legume species. With these results together with data from other approaches, the goal is to establish databases of rhizobia to provide information and cultures to microbiologists who are interested in developing optimal formulations of legume inoculants for use in agriculture, reforestation, erosion control and bioremediation.

Technical Abstract: LMW RNA profiles of 179 isolates from Medicago, Melilotus and Trigonella species growing in a field site in northern Spain were analysed. Four different LMW RNA profiles designated I through IV were identified. Most of the isolates displayed either LMW RNA profile I or III (37 and 45%, respectively), which were those identified in Sinorhizobium meliloti ATCC 9930T and Sinorhizobium medicae USDA 1037T, respectively. Almost all of the M. officinalis isolates exhibited LMW RNA profile I which also predominated among the isolates from Melilotus alba, Melilotus officinalis, Medicago sativa and Trigonella monspelliaca. Most of the isolates with LMW RNA profile III originated from Melilotus parviflora, Medicago sphaerocarpa, Medicago lupulina and Trigonella foenum-graecum. LMW RNA profiles II and IV were distinguished among a small number of the isolates. Although not identical, the LMW RNA profiles II and IV were similar to profiles I and III, respectively. From partial sequences of atpD and recA as well as DNA-DNA hybridization analysis with representatives it became evident that isolates with LMW RNA profiles II and IV could be classified as S. meliloti and S. medicae, respectively. Therefore, two different LMW RNA profiles were revealed within each of the species S. meliloti and S. medicae.