The aims of this study were to isolate and characterize N -fixing bacteria from giant reed and switchgrass and evaluate their plant growth promotion and nutrient uptake potential for use as biofertilizers. A total of 190 bacteria were obtained from rhizosphere soil and inside stems and roots of giant reed and switchgrass. All the isolates were confirmed to have nitrogenase activity, 96.9% produced auxin, and 85% produced siderophores. Then the top six strains, including Sphingomonas trueperi NNA-14, Sphingomonas trueperi NNA-19, Sphingomonas trueperi NNA-17, Sphingomonas trueperi NNA-20, Psychrobacillus psychrodurans NP-3, and Enterobacter oryzae NXU-38, based on nitrogenase activity, were inoculated on maize and wheat seeds in greenhouse tests to assess their potential benefits to plants. All the selected strains promoted plant growth by increasing at least one plant growth parameter or increasing the nutrient concentration of maize or wheat plants. NNA-14 outperformed others in promoting early growth and nutrient uptake by maize. Specifically, NNA-14 significantly increased root length, surface area, and fine roots of maize by 14%, 12%, and 17%, respectively, and enhanced N, Ca, S, B, Cu, and Zn in maize. NNA-19 and NXU-38 outperformed others in promoting both early growth and nutrient uptake by wheat. Specifically, NNA-19 significantly increased root dry weight and number of root tips of wheat by 25% and 96%, respectively, and enhanced Ca in wheat. NXU-38 significantly increased root length, surface area, and fine roots of wheat by 21%, 13%, and 26%, respectively, and enhanced levels of Ca and Mg in wheat. It is concluded that switchgrass and giant reed are colonized by N -fixing bacteria that have the potential to contribute to plant growth and nutrient uptake by agricultural crops.
A yellow, nitrogen-fixing bacterial strain, NXU-44 T , isolated from the rhizosphere of switchgrass (Panicum virgatum) in Auburn, Alabama, USA, was studied to determine its taxonomic position. Cells of the isolate were rod-shaped and Gram-stain-negative. A comparison of the 16S rRNA gene sequence with the sequences of the type strains of the most closely related species showed that the strain belongs to the genus Flavobacterium with highest sequence similarities to the type strains of Flavobacterium ginsenosidimutans (97.9 %), Flavobacterium phragmitis (97.6 %) and Flavobacterium anhuiense (97.5 %). The 16S rRNA gene sequence similarities to all other species of the genus Flavobacterium were below 97.5 %. The fatty acid profile of strain NXU-44 T consisted of the major fatty acids iso-C 15 : 0 , iso-C 15 : 0 2-OH/C 16 : 1 v7c and iso-C 17 : 0 3-OH. The major compounds in the polar lipid profile were phosphatidylethanolamine, phosphatidylserine, one aminolipid and two polar lipids. The quinone system was composed exclusively of menaquinone MK-6. The polyamine pattern contained the major compound sym-homospermidine and only minor amounts of other polyamines. The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid. These data and the differential biochemical and chemotaxonomic properties show that strain NXU-44 T represents a novel species of the genus Flavobacterium for which the name Flavobacterium nitrogenifigens sp. nov. is proposed. The type strain is NXU-44 T (5LMG 28694 T 5CIP 110894 T ).
Limited information is available on the performance of plant growth‐promoting inoculants or bioproducts under different soil nutritional or fertility conditions. Consequently, the objective of this study was to evaluate the effects of a commercially available Bacillus‐containing bioproduct, Microlife Abundance, at concentrations of 5.5 and 6.5 log cfu/ml on early growth, fertilizer use–efficiency, and fruit yield of bell pepper (Capsicum annuum L.) under two different soil fertility conditions (25% and 100% recommended N rates). Two pot experiments were conducted with bell pepper: (a) a 4‐week‐long early growth test with inoculant treatments applied once at transplanting; and (b) a 13‐week‐long yield test with inoculant treatments applied at transplanting and again at first blossom‐set. Results from the early growth test indicated that at both N fertilization levels, applying Abundance once at transplanting at 6.5 log cfu/ml rather than 5.5 log cfu/ml significantly increased root dry weight, total root length, root volume, root surface area, and total length of very fine roots compared with the noninoculated control by 20%, 13%, 17%, 15%, and 12%, respectively. In contrast to the early growth, results from the yield test showed that only at the 100% recommended N rate, applying Abundance twice at both concentrations significantly enhanced N fertilizer use–efficiency and marketable yield of bell pepper over the noninoculated control by 34% (5.5 log cfu/ml) and 30% (6.5 log cfu/ml). Therefore, the efficacy of the Bacillus‐containing bioproduct Abundance in enhancing fertilizer use–efficiency and marketable yield of bell pepper varied between soil nutritional conditions, but the early growth promotion effect of Abundance did not. Our results also demonstrate that selected microbial‐based bioproducts, like Abundance, can be compatible with chemical fertilizers to enhance fertilizer use–efficiency and crop yields, but cannot be used as complete substitutes for chemical fertilizers.
A Gram-staining-negative non endospore-forming strain, PXU-55T, was isolated from the rhizosphere of the switchgrass Panicum virgatum and studied in detail to determine its taxonomic position. The results of 16S rRNA gene sequence analysis indicated that the isolate represented a member of the genus Flavobacterium . The isolate shared highest 16S rRNA gene sequence similarities with the type strains of Flavobacterium chungangense (98.78 %) and Flavobacterium chilense (98.64 %). The average nucleotide identity (ANI) and in silico DNA–DNA hybridization (isDDH) values between the PXU-55T genome assembly and the ones of the most closely related type strains of species of the genus Flavobacterium were 87.3 and 31.9% ( Flavobacterium defluvii ), and 86.1 and 29.9% ( Flavobacterium johnsoniae ). Menaquinone MK-6 was the major respiratory quinone. As major polar lipids, phosphatidylethanolamine, an ornithine lipid and the unidentified polar lipids L2, L3 and L4 lacking a functional group were found. Moderate to minor amounts of another ornithine lipid, the unidentified lipid L1 and a glycolipid were present, as well. The major polyamine is sym-homospermidine. The fatty acid profiles contained major amounts of iso-C15:0, iso-C15:0 3-OH, iso-C17:0 3-OH, C15:0, summed feature 3 (C16:1ω7c and/or iso-C15:0 2-OH) and various hydroxylated fatty acids in smaller amounts, among them iso C16:0 3-OH, C16:0 3-OH and C15:0 3-OH, which supported the classification of the isolate as a member of the genus Flavobacterium . Physiological and biochemical characterisation and ANI calculations with the type strains of the most closely related species allowed a clear phenotypic and genotypic differentiation of the strain. For this reason, we propose that strain PXU-55T (=CIP 111646T=CCM 8914T) represents a novel species with the name Flavobacterium panici sp. nov.
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