Potential of some microbial isolates on diesel hydrocarbons removal, bio surfactant production and biofilm formation.

Potential of Arthrobacter citreus B27Pet, Bacillus thuringiensis B48Pet and Candida catnulata to produce biosurfactant using four different carbon sources (naphthalene, hexadecane, diesel and petroleum crude oil) was investigated. Removal of petroleum crude oil from aqueous culture and degradation of diesel were also determined using single and mixed culture of strains. The biofilm existence in single and mixed culture of strains was considered using naphthalene, hexadecane and diesel in culture medium. Cell surface hydrophobicity of A. citreus was higher than other isolates which also showed maximum surface tension reduction and emulsification index. As a whole, remarkable biosurfactant production occurred using petroleum crude oil as a carbon source in medium. A. citreus was found to be more robust than other tested strains in removal efficiency of crude oil due to its biosurfactant production capability. Statistically significant positive correlation was observed between biofilm existence and surface tension using diesel and hexadecane as carbon source. Overall diesel biodegradation efficiency by the mix culture of three applied strains was about 75% within a short period of time (10 days) which was accompanied with high biofilm production.

Rhizobacteria modify soil biological indices and induce tolerance to osmotic stress in tomato depending on the salinity level and bacteria species.

Salinity is a major abiotic stress that impacts crop productivity globally. Plant growth-promoting rhizobacteria (PGPRs) exploit several mechanisms to not only decrease soil salinity but also improve the systemic tolerance of plants to osmotic stress. In this work, the effect of five PGPR strains was investigated on the growth and physiological responses of tomato plants, including stomatal closure, proline, and K+ and Na+ content under a range of salt stress, 0, 2.5, 5, 7.5, and 10 dS m-1. The effect of PGPR strains and salinity levels on the soil biological characteristics was also investigated. Salt stress affected the plant growth and physiological factors and soil biological factors in a dose-dependent manner. The highest saline stress, 10 dS m-1, reduced shoot and root dry weight and root volume up to 51.3, 41.5, and 51.8%, respectively. It also increased stomatal resistance and proline content 2.01- and 3.66-folds and decreased K+/Na+ ratio 4.16-folds, respectively. It also reduced basal respiration, substrate-induced respiration, and microbial biomass carbon up to 2.25-, 4.83-, and 6.7-folds and increased qCO2 3.18-folds, respectively. PGPR strains were able to modulate salt tolerance mechanisms, improve plant growth factors, and improve soil biological indicators. Bacillus megaterium P2 was the best strain in the balancing K+/Na+ uptake at least at 10 dS m-1. However, the efficiency of strains was dependent on the magnitude of salt stress. Therefore, it is possible to introduce PGPR strains based on soil salt level or exploit rhizobacteria consortia to manage salt stress in different conditions.