Aims:  This study was conducted to test the hypothesis that the bacterial strains possessing 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐deaminase activity may also promote growth of inoculated plants and could increase nodulation in legumes upon co‐inoculation with rhizobia. Methods and Results:  Several rhizobacteria were isolated from maize rhizosphere through enrichment on ACC as a sole N source. Purified isolates were screened for growth promotion in maize under axenic conditions and for in vitro ACC‐deaminase activity. A significant positive correlation was observed between in vitro ACC‐deaminase activity of bacterial cells and root elongation. None of the isolates produced auxins. Bradyrhizobiumjaponicum produced less amount of auxins but did not carry ACC‐deaminase activity. Results of pot experiment revealed that co‐inoculation with Bradyrhizobium and plant growth promoting rhizobacteria (PGPR) isolates enhanced the nodulation in mung bean compared with inoculation with Bradyrhizobium alone. Conclusions:  It is highly expected that inoculation with rhizobacteria containing ACC‐deaminase hydrolysed endogenous ACC into ammonia and α‐ketobutyrate instead of ethylene. Consequently, root and shoot growth as well as nodulation were promoted. Significance and Impact of the Study:  The ACC‐deaminase trait could be employed as an efficient tool to screen effective PGPR, which could be successfully used as biofertilizers to increase the growth of inoculated plants as well as nodulation in legumes.

Acquisition of nutrients by plants is primarily dependent on root growth and bioavailability of nutrients in the rooting medium. Most of the beneficial bacteria enhance root growth, but their effectiveness could be influenced by the nutrient status around the roots. In this study, two 1-aminocyclopropane-1-carboxylate (ACC)-deaminase containing plant-growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens and P. fluorescens biotype F were tested for their effect on growth, yield, and nutrient use efficiency of wheat under simultaneously varying levels of all the three major nutrients N, P, and K (at 0%, 25%, 50%, 75%, and 100% of recommended doses). Results of pot and field trials revealed that the efficacy of these strains for improving growth and yield of wheat reduced with the increasing rates of NPK added to the soil. In most of the cases, significant negative linear correlations were recorded between percentage increases in growth and yield parameters of wheat caused by inoculation and increasing levels of applied NPK fertilizers. It is highly likely that under low fertilizer application, the ACC-deaminase activity of PGPR might have caused reduction in the synthesis of stress (nutrient)-induced inhibitory levels of ethylene in the roots through ACC hydrolysis into NH(3) and alpha-ketobutyrate. The results of this study imply that these Pseudomonads could be employed in combination with appropriate doses of fertilizers for better plant growth and savings of fertilizers.

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Different microbial groups of the microbiome of fresh produce can have diverse effects on human health. This study was aimed at identifying some microbial communities of fresh produce by analyzing 105 samples of imported fresh fruits and vegetables originated from different countries in the world including local samples (Oman) for aerobic plate count and the counts of Enterobacteriaceae, Enterococcus, and Staphylococcus aureus. The isolated bacteria were identified by molecular (PCR) and biochemical methods (VITEK 2). Enterobacteriaceae occurred in 60% of fruits and 91% of vegetables. Enterococcus was isolated from 20% of fruits and 42% of vegetables. E. coli and S. aureus were isolated from 22% and 7% of vegetables, respectively. Ninety-seven bacteria comprising 21 species were similarly identified by VITEK 2 and PCR to species level. E. coli, Klebsiella pneumoniae, Enterococcus casseliflavus, and Enterobacter cloacae were the most abundant species; many are known as opportunistic pathogens which may raise concern to improve the microbial quality of fresh produce. Phylogenetic trees showed no relationship between clustering of the isolates based on the 16S rRNA gene and the original countries of fresh produce. Intercountry passage of opportunistic pathogens in fresh produce cannot be ruled out, which requires better management.