Pulsed electromagnetic fields induced femoral metaphyseal bone thickness changes in the rat.

The effect of 1 Hz, 30 mT pulsed magnetic fields on young adult rat femoral metaphyseal bone thickness was assessed. Ten same litter, female Wistar rats were studied; five of them underwent 30 min magnetic stimulation sessions for 20 consecutive days. The anterior and posterior cortical, as well as trabecular bone transverse thicknesses were measured. The results obtained under clear field microscopy in stimulated and control histological cuts were (in microm) 398 +/- 32 versus 260 +/- 22 (P = 0.002), 380 +/- 68 versus 252 +/- 21 (P = 0.03), and 168 +/- 11 versus 112 +/- 11 (P = 0.002), respectively. The transcranial magnetic stimulation system, approved for human therapy, generates pulsed electromagnetic fields, which induce a significant thickness increase in cortical and trabecular in vivo stimulated bone tissues. This is the first time this effect in healthy animals is shown.

Transformation of Azospirillum brasilense Cd with an ACC deaminase gene from enterobacter cloacae UW4 fused to the Tet r gene promoter improves its fitness and plant growth promoting ability.

It has been reported that PGPB, containing ACC deaminase, can cleave the plant ethylene precursor ACC and thereby lower ethylene concentration in a developing or stressed plant, protecting it against the deleterious effects of stress ethylene and facilitating the formation of longer roots. In a previous work we have demonstrated expression of the ACC deaminase gene ( acdS) from Enterobacter cloacae UW4 under the control of the lac promoter in Azospirillum brasilense Cd. With the inference that a construct including the ACC deaminase gene under the control of a constitutive promoter weaker than the lac promoter might impose less metabolic load on Azospirillum and improve its fitness, it was decided to clone acdS under the control of a tetracycline resistance gene promoter. The ACC deaminase structural gene was fused to the Tet(r) gene promoter by overlap extension using PCR, cloned in pRK415, and transferred into A. brasilense Cd. The resulting transformants showed lower ACC deaminase activity than those with the lac promoter controlled acdS gene. However, acdS under the control of the Tet(r) gene promoter imposed lesser metabolic load on Azospirillum brasilense Cd. The result was significantly increased IAA synthesis and greater bacterial growth rate, as well as increased ability to survive on the surface of tomato leaves and to promote the growth of tomato seedlings.

Expression of the ACC Deaminase Gene fromEnterobacter cloacae UW4 in Azospirillum brasilense.

The ACC deaminase structural gene (acdS) from Enterobacter cloacae UW4 was cloned in the broad host range plasmid pRK415 under the control of the lac promoter and transferred into Azospirillum brasilense Cd and Sp245. A. brasilenseCd and Sp245 transformants showed high ACC deaminase activity, similar to that observed in Enterobacter cloacae UW4. The expression of ACC deaminase improved the existing growth promoting activity of Azospirillum. The roots of tomato and canola seedlings were significantly longer in plants inoculated with A. brasilense Cd transformants than those in plants inoculated with the nontransformed strains of the same bacterium. In the case of wheat seedlings, inoculation with A. brasilense Cd transformants did not promote root growth. The difference in plant response (canola and tomato versus wheat) is attributed to the greater sensitivity of canola and tomato plants to ethylene as compared to wheat plants.

Synergism between Phyllobacterium sp. (N(2)-fixer) and Bacillus licheniformis (P-solubilizer), both from a semiarid mangrove rhizosphere.

Mangrove seedlings were treated with a mixture of two bacterial species, the slow-growing, N(2)-fixing bacterium Phyllobacterium sp. and the fast-growing, phosphate-solubilizing bacterium Bacillus licheniformis, both isolated from the rhizosphere from black, white, and red mangroves of a semiarid zone. Nitrogen fixation and phosphate solubilization increased when the mixture was used compared to the effects observed when adding individual cultures, notwithstanding that there was no increase in bacterial multiplication under these conditions. Inoculation of black mangrove seedlings in artificial seawater showed the mixture performed somewhat better than inoculation of the individual bacterium; more leaves were developed and higher levels of (15)N were incorporated into the leaves, although the total nitrogen level decreased. This study demonstrates that interactions between individual components of the rhizosphere of mangroves should be considered when evaluating these bacteria as plant growth promoters.

Survival of Azospirillum brasilense in the Bulk Soil and Rhizosphere of 23 Soil Types.

The survival of Azospirillum brasilense Cd and Sp-245 in the rhizosphere of wheat and tomato plants and in 23 types of plant-free sterilized soils obtained from a wide range of environments in Israel and Mexico was evaluated. Large numbers of A. brasilense cells were detected in all the rhizospheres tested, regardless of soil type, bacterial strain, the origin of the soil, or the amount of rainfall each soil type received prior to sampling. Survival of A. brasilense in soils without plants differed from that in the rhizosphere and was mainly related to the geographical origin of the soil. In Israeli soils from arid, semiarid, or mountain regions, viability of A. brasilense rapidly declined or populations completely disappeared below detectable levels within 35 days after inoculation. In contrast, populations in the arid soils of Baja California Sur, Mexico, remained stable or even increased during the 45-day period after inoculation. In soils from Central Mexico, viability slowly decreased with time. In all soils, percentages of clay, nitrogen, organic matter, and water-holding capacity were positively correlated with bacterial viability. High percentages of CaCO(inf3) and fine or rough sand had a highly negative effect on viability. The percentage of silt, pH, the percentage of phosphorus or potassium, electrical conductivity, and C/N ratio had no apparent effect on bacterial viability in the soil. Fifteen days after removal of inoculated plants, the remaining bacterial population in the three soil types tested began to decline sharply, reaching undetectable levels 90 days after inoculation. After plant removal, percolating the soils with water almost eliminated the A. brasilense population. Viability of A. brasilense in two artificial soils containing the same major soil components as the natural soils from Israel did was almost identical to that in the natural soils. We conclude that A. brasilense is a rhizosphere colonizer which survives poorly in most soils for prolonged periods of time; that outside the rhizosphere, seven abiotic parameters control the survival of this bacterium in the soil; and that disturbance of the soil (percolation with water or plant removal) directly and rapidly affects the population levels.

Inter-root movement of Azospirillum brasilense and subsequent root colonization of crop and weed seedlings growing in soil.

Inter-root movement and dispersion of the beneficial bacterium Azospirillum brasilense were monitored in root systems of wheat seedlings growing in the field and in growth chamber soil trays. Two strains were used, a motile wild-type strain (Cd, mot(+)) and a motility deficient strain (mot(-)), which was derived from the Cd strain. Root colonization by two wild-type strains (Cd and Sp-245) was studied in 64 plant species growing in pots in the greenhouse. The two wild-type strains of A. brasilense were capable of colonizing all tested plant species. In soil trays and in the field, mot(+) cells moved from inoculated roots to non-inoculated roots of either wheat plants or weeds growing in the same field plot, but the mot(-) strain did not move toward non-inoculated roots of either plant species. In the field, both mot(+) and mot(-) strains of A. brasilense survived well in the rhizosphere of wheat for 30 days, but only mot(+) moved between different weeds, regardless of the species, botanical family, or whether they were annuals or perennials. In plant-free, water-saturated soils, either in columns or in the field, both strains remained at the inoculation site and did not move.It is proposed (a) that A. brasilense is not a plant-specific bacterium and that (b) colonization of the entire root system in soil is an active process determined by bacterial motility; it is not plant specific, but depends on the presence of plants.

Root-to-Root Travel of the Beneficial Bacterium Azospirillum brasilense.

The root-to-root travel of the beneficial bacterium Azospirillum brasilense on wheat and soybean roots in agar, sand, and light-textured soil was monitored. We used a motile wild-type (Mot) strain and a motility-deficient (Mot) strain which was derived from the wild-type strain. The colonization levels of inoculated roots were similar for the two strains. Mot cells moved from inoculated roots (either natural or artificial roots in agar, sand, or light-textured soil) to noninoculated roots, where they formed a band-type colonization composed of bacterial aggregates encircling a limited part of the root, regardless of the plant species. The Mot strain did not move toward noninoculated roots of either plant species and usually stayed at the inoculation site and root tips. The effect of attractants and repellents was the primary factor governing the motility of Mot cells in the presence of adequate water. We propose that interroot travel of A. brasilense is an essential preliminary step in the root-bacterium recognition mechanism. Bacterial motility might have a general role in getting Azospirillum cells to the site where firmer attachment favors colonization of the root system. Azospirillum travel toward plants is a nonspecific active process which is not directly dependent on nutrient deficiency but is a consequence of a nonspecific bacterial chemotaxis, influenced by the balance between attractants and possibly repellents leaked by the root.

Susceptibility of the brine shrimp Artemia and its pathogen Vibrio parahaemolyticus to chlorine dioxide in contaminated sea-water.

Adults and nauplii of the brine shrimp, Artemia, together with Vibrio parahaemolyticus, were placed in sewage-contaminated sea-water which had been treated with chlorine dioxide (Hallox E-100TM) to test its potential as a disinfectant for salt water aquaculture. The nauplii were very susceptible to low concentrations of chlorine dioxide (47 micrograms/l Cl-), but the adults were slightly more resistant. Sterile sea-water treated with lower concentrations of chlorine dioxide (less than 47 micrograms/l Cl-) had no effect on the shrimp, but inhibited the growth of V. parahaemolyticus. In sewage-contaminated sea-water, chlorine dioxide levels of 285-2850 micrograms/l, necessary for the inactivation of V. parahaemolyticus and any native bacteria, destroyed the Artemia culture. Hallox E-100TM persisted in sea-water for 18 h, but later decayed. We conclude that: (i) Artemia nauplii are a sensitive and convenient test-organism to determine low concentrations of chlorine dioxide in sea-water; (ii) chlorine dioxide is efficient for controlling V. parahaemolyticus in sea-water; and (iii) chlorine dioxide should be further evaluated as a potential disinfectant for aquaculture, but, for higher organisms than Artemia.