Pseudomonas fluorescens LBUM677 differentially increases plant biomass, total oil content and lipid composition in three oilseed crops.

AIMS: Pseudomonas spp. have been widely studied for their plant growth-promoting effects. However, their capacity to promote lipid accumulation in oilseed crops is not well characterized. In this study, we evaluated the effect of Pseudomonas fluorescens LBUM677 on lipid accumulation in three oilseed crops: soybean (Glycine max), canola (Brassica napus) and corn gromwell (Buglossoides arvensis), a plant of high nutraceutical interest for its accumulation of the omega-3 stearidonic acid. METHODS AND RESULTS: Pot experiments were conducted under controlled conditions where seeds were inoculated or not with LBUM677 and plants were harvested at 4, 8 and 12 weeks. A qPCR assay specifically targeting LBUM677 was used in parallel to correlate LBUM677 soil rhizosphere competency to growth promotion and seed lipid accumulation. Total oil seed content and fatty acid composition were analysed at seed maturity. Results showed that LBUM677 was able to establish itself in the rhizosphere of the three plant species at similar levels, but it differentially increased plant biomass, total oil content and lipid composition in a plant-specific manner. CONCLUSIONS: Despite some species-specific differences observed in P. fluorescens LBUM677's effect on different crops, the strain appears to be a generalist plant growth-promoting rhizobacteria of oilseed crops. SIGNIFICANCE AND IMPACT OF THE STUDY: LBUM677 shows great potential to be used as an inoculum to promote oil yield and fatty acid accumulation in oilseed crops.

Persistence of Pseudomonas fluorescens LBUM677 in the rhizosphere of corn gromwell (Buglossoides arvensis) under field conditions and its impact on seed oil and stearidonic acid bioaccumulation.

AIMS: The aim of this study was to evaluate the persistence of Pseudomonas fluorescens LBUM677 in the rhizosphere of Buglossoides arvensis under agricultural field conditions and determine if B. arvensis intraspecific genetic variations affect the capacity of LBUM677 to colonize its rhizosphere and increase seed oil and stearidonic acid (SDA) accumulation. METHODS AND RESULTS: Two field experiments were performed to: (i) study the persistence of various concentrations of LBUM677 inoculated in the rhizosphere of B. arvensis and determine a minimum inoculation threshold required to maximize biological activity; and (ii) study the impact of B. arvensis intraspecific genetic variations on LBUM677 rhizosphere colonization and seed oil and SDA accumulation. In order to track LBUM677 populations in soil over time, a specific quantitative polymerase chain reaction assay was developed. Inoculation with a minimum of 109 LBUM677 bacterial cells per plant was determined as a threshold to promote maximum B. arvensis rhizosphere colonization and seed oil and SDA accumulation. Buglossoides arvensis intraspecific genetic variations had an impact on rhizosphere colonization, B. arvensis seed oil and SDA accumulation, where two cultivars benefited more than others from LBUM677 inoculation. CONCLUSIONS: LBUM677 can colonize the rhizosphere and increase seed oil and SDA yields in B. arvensis plants in a cultivar-dependant manner. SIGNIFICANCE AND IMPACT OF THE STUDY: LBUM677 shows potential to be used as a biofertilizer to specifically increase seed oil and SDA yields in B. arvensis. This will in turn promote the development of an economically viable agricultural-based approach as an alternative for producing high-quality polyunsaturated fatty acids.

Enhancing total lipid and stearidonic acid yields in Buglossoides arvensis through PGPR inoculation.

AIM: This study was performed to identify bacterial isolates capable of enhancing total lipid and stearidonic acid (SDA) yields in Buglossoides arvensis. METHODS AND RESULTS: Pot experiments were conducted to screen the effects of 40 bacterial isolates on different B. arvensis growth parameters. Five isolates increased total lipid and SDA yields by at least 20%. These isolates were tested in a second pot experiment and in field trials. The second pot experiment confirmed that all isolates significantly increased total lipid and SDA yields over controls. Plants inoculated with four bacterial strains experienced significantly higher shoot weights, however, the increase in shoot weight decreased over time. Three isolates led to higher total seed numbers. In field trials, the inoculations had no significant effect on seed or lipid yields. However, isolate Pseudomonas fluorescens LBUM677 significantly increased SDA yield by 33% as compared to control plants. This strain was also the most efficient biofilm producer. CONCLUSIONS: Pseudomonas fluorescens LBUM677 can significantly increase SDA yield in B. arvensis under controlled and field conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Using bacterial strains to increase plant yield is of great interest under commercial settings. Pseudomonas fluorescens LBUM677 shows promise to promote SDA accumulation in B. arvensis under production conditions.

Effect of soil clay content on RNA isolation and on detection and quantification of bacterial gene transcripts in soil by quantitative reverse transcription-PCR.

In this study, we evaluated the effect of soil clay content on RNA isolation and on quantitative reverse transcription-PCR (qRT-PCR) quantification of microbial gene transcripts. The amount of clay significantly altered RNA isolation yields and qRT-PCR analyses. Recommendations are made for quantifying microbial gene transcripts in soil samples varying in clay content.

qPCR quantification and genetic characterization of Clostridium perfringens populations in biosolids composted for 2 years.

AIM: The ability of Clostridium perfringens to survive for a long time in the environment makes it a suitable indicator of faecal pollution, but its use as a routine indicator organism in biosolids and composted biosolids has not yet been adopted. This study was performed to improve our understanding of C. perfringens persistence in composted biosolids by monitoring its presence and studying its genetic diversity. METHODS AND RESULTS: A culture-independent TaqMan qPCR assay targeting the cpn60 gene was adapted to enumerate C. perfringens in composted biosolid samples varying in age from 1 to 24 months. The pathogen was detected in all compost samples under study, but no correlation between composting time and number of cpn60 copies was observed. Rep-PCR detected 14 different C. perfringens genotypes, all belonging to toxinotype A, which is the most common biotype found in human and animal gastrointestinal tracts. CONCLUSIONS: Composting did not significantly decrease the number of C. perfringens cells. High genetic diversity of C. perfringens isolates present in composted biosolids is reported for the first time. SIGNIFICANCE AND IMPACT OF STUDY: This study evaluated tools for surveillance of composting processes, source tracking and risk assessment of composted biosolids.

Application of molecular technologies to monitor the microbial content of biosolids and composted biosolids.

Disposal of human biosolids is a source of concern for public health and the environment. Composting appears to be an interesting alternative to traditional disposal methods as it can decrease the load of human pathogenic microorganisms often present in biosolids and yield an end-product rich in nutrients for use as a soil supplement. Assessing the exact microbial content of biosolids, both for biosafety and operational reasons, has traditionally relied on the use of standard microbiological methods. Recent developments in molecular-based technologies now offer more rapid and specific monitoring of microorganisms in biosolids than culture-based methods. In this study, denaturing gradient gel electrophoresis (DGGE) was adapted to monitor the succession of bacteria in composted biosolids through different steps of compost production. Secondly, a TaqMan quantitative real time PCR (qPCR) approach was developed to detect and quantify the presence of Salmonella species, a model human pathogenic bacterium, susceptible to be found in biosolids. DGGE results indicated that the bacterial content of composted biosolids of different ages belongs to various taxa and significantly changes with age. qPCR results indicated that the quantity of Salmonella species found in composted biosolids ranging from 1 to 24 months significantly decreases with composting time.