Diversity, distribution and multi-functional attributes of bacterial communities associated with the rhizosphere and endosphere of timothy (Phleum pratense L.).

AIMS: To characterize the bacterial communities of the rhizosphere and endosphere of the forage grass timothy (Phleum pratense L.) and evaluate the functional attributes with respect to growth promotion properties, antimicrobial and biosurfactant capacities. METHODS AND RESULTS: A total of 254 culturable bacteria were identified using 16S rRNA sequencing and grouped into 16 taxa that shared high homology of 98-99% with other known sequences. A majority of the isolates were recovered from the rhizosphere soil fraction and leaf and crown tissues. Bacillus genus was the most abundant in the bulk and rhizosphere soil fractions. Isolates belonging to the Methylobacterium genus were exclusively found in leaves making them tissue-specific. A majority of the bacterial isolates exhibited multi-functional growth promotion attributes and plant stress improvement related to the production of indole 3-acetic acid, VOC and siderophores and polymer-degrading enzymes and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activities. Some demonstrated antimicrobial properties such as hydrogen cyanide and biosurfactant production and activities of fungal cell wall degrading enzymes. The internalization and spread of selected bacterial isolates in timothy seedlings under gnotobiotic conditions was confirmed using the culture-dependent method and SEM microscopy in proof-of-concept experiments. CONCLUSIONS: The attributes of some isolates with respect to growth promotion abilities, biocontrol potential and efficient colonization of timothy make them desirable for future development as potential biofertilizer tools. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides the first evidence of bacterial endophytes that have the necessary functional attributes to protect cool-season forage grasses against abiotic stress.

Isolation and characterization of indigenous endophytic bacteria associated with leaves of switchgrass (Panicum virgatum L.) cultivars.

AIMS: To isolate and characterize indigenous bacterial endophytes from cultivars of switchgrass and study their antimicrobial and growth promoting potential. METHODS AND RESULTS: The diversity, molecular and biochemical characterizations of indigenous and culturable bacterial endophytes residing in leaves of switchgrass have not been studied previously. This study describes the characterization of 31 bacterial endophytes from three switchgrass cutlivars: Cave-in Rock, Blue Jacket and Tecumseh. Molecular and phylogenetic analysis based on the 16S rRNA sequence grouped the endophytes into eight different taxa that shared high homology of 98-99% with other known sequences. Bacterial endophytes were identified as Microbacterium testaceum, Curtobacterium flaccumfaciens, Bacillus subtilis and Bacillus pumilus, Pseudomonas fluorescens, Sphingomonas parapaucimobilis, Serratia sp. and Pantoea ananatis. Some endophytes were detected in switchgrass seeds and in plants that originated from seeds collected a year earlier, confirming vertical transmission to the next generation of the host. Selected endophytes produced cellulases and were capable of solubilizing inorganic phosphorus. Analysis of cell-free culture filtrate of selected strains using direct infusion orbitrap mass spectrometry confirmed the presence of several well-characterized lipopeptide toxins and phytohormones. Re-inoculation of the roots of switchgrass seedlings with endophytes singly or combined confirmed their migration to the upper aerial parts of the plant. CONCLUSIONS: Our findings suggest that switchgrass leaves harbour a diversity of bacterial endophytes, some of which could potentially be applied as growth promoting bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on the characterization of indigenous bacterial endophytes and their potential use as biofertilizers.

Honeybee glands as possible infection reservoirs of Nosema ceranae and Nosema apis in naturally infected forager bees.

AIMS: To determine whether Nosema ceranae and Nosema apis are present in different gland tissues of honeybee, Apis mellifera L. and to monitor spore presence and quantity in these glands in naturally infected hives from July 2009 to July 2010 in Quebec, Canada. METHODS AND RESULTS: Nosema spp. were quantified using duplex quantitative real-time PCR in the thoracic salivary, hypopharyngeal, mandibular glands, and venom sac and glands of A. mellifera over a period of 8 months. Both Nosema species were present in all the glands as single or mixed species; however, N. apis was not present as single-species detections in the salivary glands (see Table 2). Nosema ceranae was more prevalent throughout the 8 months. Significant correlative relationships were established for N. ceranae and N. apis levels in the honeybee glands and those found within the intestines of forager honeybees. Overall, the seasonality of N. ceranae and N. apis in the different glands tightly followed the seasonal patterns in the honeybee guts. CONCLUSIONS: Nosema ceranae and N. apis are not tissue specific, and honeybee glands have potential to become a useful indicator of the extent of disease in the colony and may represent a potential infection reservoir. SIGNIFICANCE AND IMPACT OF THE STUDY: First report of spore load quantification of Nosema spp. in different honeybee glands.