Plant–Rhizobium symbiosis, seed nutraceuticals, and waste quality for energy production of Vicia faba L. as affected by crop management

Background: Broad bean fits sustainable agriculture model due to symbiosis with Rhizobium, the seeds being a good source of energy, proteins, polyphenols, and fiber. The large amount of broad bean biomass residues can be employed for biofuel production, thus valorizing the overall production process. This research was aimed to investigate on the effects of farming management, such as greenhouse cultivation and appropriate planting time on the qualities of broad bean seeds and residual biomass for conversion into biofuel. The related balances of energy gain associated to both ethanol yield and nitrogen fertilizer saving due to Rhizobium nitrogen fixation were assessed. Methods: Research was carried out on broad bean in Portici, province of Naples, southern Italy, based on the factorial combination of two farming systems (open field, greenhouse) and five planting times: 27 September and 11 October, to obtain early production; 25 October, which fell in the usual period for broad bean planting in the province area; and 8 November and 22 November, for late production. For each of these cultivation conditions, the quality of seeds, in terms of protein, fiber and antioxidant concentrations, and of crop residual biomass were determined. In addition, the energy yield as ethanol production from residual biomass and nitrogen fertilizer saving due to Rhizobium atmospheric fixation were assessed. Results and discussion: The highest plant nitrogen uptake was recorded under the fourth planting time in open field and the third in greenhouse, the average accumulation attaining 87% in residual biomass, 7.4% in pods, and 5.6% in seeds. Seed protein content was 12.6% higher in greenhouse than in open field and 16.2% higher under the latest planting time compared to the earliest one. Seed polyphenol concentration was higher in open field than in greenhouse and with the two earliest planting times. Greenhouse grown biomass showed higher values of lignin, hemicellulose and pectin, compared to open field, whereas the opposite trend was for cellulose. Lignin showed a decrease from the first to the last crop cycle, opposite to cellulose, and glucose was the most represented monosaccharide. Both the highest theoretical ethanol and overall energy production were highest with the fourth planting time. Conclusions: Greenhouse management enabled broad bean plants to accumulate higher proteins in seeds, but open field conditions resulted in better residual biomass quality for ethanol and Rhizobium-depending energy production

Coevolution with viruses drives the evolution of bacterial mutation rates

Bacteria with greatly elevated mutation rates ( mutators) are frequently found in natural(1-3) and laboratory(4,5) populations, and are often associated with clinical infections(6,7). Although mutators may increase adaptability to novel environmental conditions, they are also prone to the accumulation of deleterious mutations. The long-term maintenance of high bacterial mutation rates is therefore likely to be driven by rapidly changing selection pressures(8-14), in addition to the possible slow transition rate by point mutation from mutators to non- mutators(15). One of the most likely causes of rapidly changing selection pressures is antagonistic coevolution with parasites(16,17). Here we show whether coevolution with viral parasites could drive the evolution of bacterial mutation rates in laboratory populations of the bacterium Pseudomonas fluorescens(18). After fewer than 200 bacterial generations, 25% of the populations coevolving with phages had evolved 10- to 100- fold increases in mutation rates owing to mutations in mismatch-repair genes; no populations evolving in the absence of phages showed any significant change in mutation rate. Furthermore, mutator populations had a higher probability of driving their phage populations extinct, strongly suggesting that mutators have an advantage against phages in the coevolutionary arms race. Given their ubiquity, bacteriophages may play an important role in the evolution of bacterial mutation rates