Evaluation of biphenyl- and polychlorinated-biphenyl (PCB) degrading Rhodococcus sp. MAPN-1 on growth of Morus alba by pot study.

This study focused on isolation of bacteria with biphenyl/polychlorinated biphenyl (PCB) degrading ability from the rhizosphere of Morus alba (mulberry plant). Repetitive enrichment of rhizospheric soil samples with biphenyl resulted in the isolation of Rhodococcus sp. MAPN-1, identified by 16S rRNA gene sequence analysis. The bacterium showed growth on five different aromatic compounds (naphthalene, salicylic acid, benzoic acid, dibenzofuran and anthracene). Benzoic acid was detected as the major metabolite during biphenyl degradation using high-performance thin-layer chromatography (HPTLC) with Rf 0.42 at 254 nm. Further GC-MS/MS study showed 95% and 15% degradation of biphenyl and dichlorobiphenyl, respectively. A pot study was conducted to evaluate the effect of presence of biphenyl on M. alba and the role of biphenyl degrader Rhodococcus sp. MAPN-1 in relation to phytoremediation. Morus alba twigs in biphenyl spiked soil (100 mg/kg and 300 mg/kg) inoculated with Rhodococcus sp. MAPN-1 showed growth, whereas, growth of plants (control) was adversely affected in biphenyl-spiked uninoculated soil. It is the first report of isolation of Rhodococcus sp. MAPN-1 from the rhizosphere of Morus alba, its capability to degrade biphenyl, thereby showing a positive effect on the plant growth grown in biphenyl spiked soil.

The PGPR Stenotrophomonas maltophilia SBP-9 Augments Resistance against Biotic and Abiotic Stress in Wheat Plants.

Certain plant growth promoting bacteria have ability to ameliorate abiotic and/or biotic stressors, which can be exploited to enhance plant growth and productivity of the plants under stress conditions. Therefore, the present study aimed to examine the role of a rhizospheric bacterial isolate SBP-9 isolated from Sorghum bicolor (i) in promoting the wheat plant growth under salinity stress, and (ii) in enhancing the defense response in wheat against fungal pathogen "Fusarium graminearum." The test isolate possessed plant growth promoting (PGP) traits including ACC deaminase (ACCD), gibberellic acid, indole acetic acid (IAA), siderophore, and inorganic phosphate solubilization. Under salt (NaCl) stress, inoculation of this isolate to wheat plant significantly increased plant growth in terms of various growth parameters such as shoot length/root length (20-39%), fresh weight/dry weight (28-42%), and chlorophyll content (24-56%) following inoculation of test isolate SBP-9. Bacterial inoculation decreased the level of proline, and malondialdehyde, whereas elevated the antioxidative enzymatic activities of superoxide-dismutase (SOD; 28-41%), catalase (CAT; 24-56%), and peroxidase (POX; 26-44%). Furthermore, it also significantly decreased the Na+ accumulation in both shoot and roots in the range of 25-32%, and increased the K+ uptake by 20-28%, thereby favoring the K+/Na+ ratio. On the other hand, the test isolate also enhanced the level of defense enzymes like ß-1, 3 glucanase, phenylalanine ammonia lyase (PAL), peroxidae (PO), and polyphenol oxidase (PPO), which can protect plants from the infection of pathogens. The result of colonization test showed an ability of the test isolate to successfully colonize the wheat plants. These results indicate that Stenotrophomonas maltophilia SBP-9 has potential to promote the wheat growth under biotic and abiotic (salt) stressors directly or indirectly and can be further tested at field level for exploitation as bioinoculant.

A Halotolerant Bacterium Bacillus licheniformis HSW-16 Augments Induced Systemic Tolerance to Salt Stress in Wheat Plant (Triticum aestivum).

Certain plant growth promoting bacteria can protect associated plants from harmful effects of salinity. We report the isolation and characterization of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase bacterium Bacillus licheniformis HSW-16 capable of ameliorating salt (NaCl) stress in wheat plants. The bacterium was isolated from the water of Sambhar salt lake, Rajasthan, India. The presence of ACC deaminase activity was confirmed by enzyme assay and analysis of AcdS gene, a structural gene for ACC deaminase. Inoculation of B. licheniformis HSW-16 protected wheat plants from growth inhibition caused by NaCl and increased plant growth (6-38%) in terms of root length, shoot length, fresh weight, and dry weight. Ionic analysis of plant samples showed that the bacterial inoculation decreased the accumulation of Na+ content (51%), and increased K+ (68%), and Ca2+ content (32%) in plants at different concentration of NaCl. It suggested that bacterial inoculation protected plants from the effect of NaCl by decreasing the level of Na+ in plants. Production of exopolysaccharide by the B. licheniformis HSW-16 can also protect from Na+ by binding this ion. Moreover, application of test isolate resulted in an increase in certain osmolytes such as total soluble sugar, total protein content, and a decrease in malondialdehyde content, illustrating their role in the protection of plants. The ability of B. licheniformis HSW-16 to colonize plant root surface was examined by staining the bacterium with acridine orange followed by fluorescence microscopy and polymerase chain reaction-based DNA finger printing analysis. These results suggested that B. licheniformis HSW-16 could be used as a bioinoculant to improve the productivity of plants growing under salt stress.

Corrigendum: Biochemistry and genetics of ACC deaminase: a weapon to "stress ethylene" produced in plants.

[This corrects the article on p. 937 in vol. 6, PMID: 26441873.].

Biochemistry and genetics of ACC deaminase: a weapon to "stress ethylene" produced in plants.

1-aminocyclopropane-1-carboxylate deaminase (ACCD), a pyridoxal phosphate-dependent enzyme, is widespread in diverse bacterial and fungal species. Owing to ACCD activity, certain plant associated bacteria help plant to grow under biotic and abiotic stresses by decreasing the level of "stress ethylene" which is inhibitory to plant growth. ACCD breaks down ACC, an immediate precursor of ethylene, to ammonia and α-ketobutyrate, which can be further metabolized by bacteria for their growth. ACC deaminase is an inducible enzyme whose synthesis is induced in the presence of its substrate ACC. This enzyme encoded by gene AcdS is under tight regulation and regulated differentially under different environmental conditions. Regulatory elements of gene AcdS are comprised of the regulatory gene encoding LRP protein and other regulatory elements which are activated differentially under aerobic and anaerobic conditions. The role of some additional regulatory genes such as AcdB or LysR may also be required for expression of AcdS. Phylogenetic analysis of AcdS has revealed that distribution of this gene among different bacteria might have resulted from vertical gene transfer with occasional horizontal gene transfer (HGT). Application of bacterial AcdS gene has been extended by developing transgenic plants with ACCD gene which showed increased tolerance to biotic and abiotic stresses in plants. Moreover, distribution of ACCD gene or its homolog's in a wide range of species belonging to all three domains indicate an alternative role of ACCD in the physiology of an organism. Therefore, this review is an attempt to explore current knowledge of bacterial ACC deaminase mediated physiological effects in plants, mode of enzyme action, genetics, distribution among different species, ecological role of ACCD and, future research avenues to develop transgenic plants expressing foreign AcdS gene to cope with biotic and abiotic stressors. Systemic identification of regulatory circuits would be highly valuable to express the gene under diverse environmental conditions.