Molecular mechanisms underlying heat or tetracycline treatments for citrus HLB control

Huanglongbing(HLB),a destructive plant bacterial disease,severely impedes worldwide citrus production.In our previous reports,we revealed the molecular mechanisms of host plant responses that underlie thermotherapy against HLB.In this study,we investigated the molecular mechanism underlying heat or tetracycline treatments on the HLB bacterium,‘Candidatus Liberibacter asiaticus’(Las)by focusing on Las prophage/phage conversion under stress conditions.By comparing the prophage FP1 and FP2 copy number to the copy number of 16S rDNA in HLB-affected plants,we found that the relative copy number of both FP1 and FP2 increased significantly,ranging from 3.4-to 6.7-fold change when Las-infected samples underwent a temperature shift from 23 to 37,42 or 45°C.When treated with tetracycline at 50–150 and 200–250µg/ml,respectively,the relative copy number of both FP1 and FP2 increased by 3.4-to 6.0-fold.In addition,analyses of Las prophage structural gene and antirepressor gene copy numbers showed similar trends for all treatments.Furthermore,transmission electron microscopy provided direct evidence of lysogenic to lytic conversion upon temperature increase.These results not only provide new insight into the molecular mechanisms underlying heat or tetracycline treatment but also suggest a novel HLB control strategy by enhancing the endogenous conversion from Las prophages to phages.

Potential Approaches to Improving Biodegradation of Hydrocarbons for Bioremediation of Crude Oil Pollution

With increasing demands of fossil fuel energy, extensive exploration of natural sources has caused a number of large scale accidental spills of crude oil and resulted in some significantly environmental disasters. The consequence of oil pollution to environment and human health has brought a serious challenge to environmental scientists. Physical and chemical approaches to cleanup oil spills are too expensive and create adverse effects. Bioremediation has shown a great potential and competitive privilege because of environment friendly and cost effective. A number of efficient microbial strains have been identified and isolated, which can effectively degrade various components of petroleum oil. However, the biodegradation efficiency is usually limited by abiotic factors, such as temperature and pH, which are hardly to be controlled in the in situ condition but adequate oxygen supply and nutrient balancing are of importance to impact microbial functions. Therefore, this review especially addresses potential approaches to improving bioremediation of crude oil by supplying solid oxygen and adjusting C: N: P ratio to optimize microbial activities in order to improve the effectiveness and efficacy of bioremediation of crude oil pollutants. In addition, it also elucidates advantages of bioremediation, isolation of selective microbial strains, and evaluation of the biodegradation rates.

Effects of Plant Growth-Promoting Rhizobacteria and N Source on Plant Growth and N and P Uptake by Tomato Grown on Calcareous Soils

Introducing specific microorganisms into the soil ecological system is an important strategy for improving nutrient use efficiency.Two pot experiments were conducted in the greenhouse from December 3, 2012 to January 25, 2013(Experiment 1) and March 11 to April 23, 2013(Experiment 2) to evaluate the effect of nitrogen(N) source and inoculation with plant growth-promoting rhizobacteria(PGPR) on plant growth and N and phosphorus(P) uptake in tomato(Lycopersicon esculentum Mill.) grown on calcareous soils from South Florida, USA.Treatments included urea, controlled release urea(a controlled release fertilizer, CRF) each at low and high N rates and with or without inoculation of PGPR.A mixture of PGPR strains Bacillus amyloliquefaciens IN937 a and Bacillus pumilus T4 was applied to the soil during growing periods of tomato.Treatments with PGPR inoculation increased plant height compared to treatments without PGPR in both experiments.Inoculation with PGPR increased shoot dry weight and shoot N uptake for the same N rate and N source.In both experiments, only at high N rate, CRF and urea treatments with PGPR had significantly(P < 0.05)greater shoot biomass than those without PGPR.Only at high N rate, CRF treatment with PGPR significantly increased shoot N uptake by 39.0% and 10.3% compared to that without PGPR in Experiments 1 and 2, respectively.Meanwhile, presence of PGPR in the soil increased shoot P uptake for all treatments in Experiment 1 and for most treatments in Experiment 2.In Experiment 1, only at low N rate, CRF treatment with PGPR significantly increased shoot P uptake compared with that without PGPR.In Experiment2, a significant increase in shoot P uptake by inoculation of PGPR was only observed in CRF treatment at high N rate.Results from this study indicate that inoculation with PGPR may increase plant growth and N and P uptake by tomato grown on calcareous soils.However, the effect of PGPR varied and was influenced by many factors such as N source, N rate, and soil fertility.Further investigations are warranted to confirm the effect of PGPR under different soil conditions.