Bioremediation assessment of diesel-biodiesel-contaminated soil using an alternative bioaugmentation strategy.

This study investigated the effectiveness of successive bioaugmentation, conventional bioaugmentation, and biostimulation of biodegradation of B10 in soil. In addition, the structure of the soil microbial community was assessed by polymerase chain reaction-denaturing gradient gel electrophoresis. The consortium was inoculated on the initial and the 11th day of incubation for successive bioaugmentation and only on the initial day for bioaugmentation and conventional bioaugmentation. The experiment was conducted for 32 days. The microbial consortium was identified based on sequencing of 16S rRNA gene and consisted as Pseudomonas aeruginosa, Achromobacter xylosoxidans, and Ochrobactrum intermedium. Nutrient introduction (biostimulation) promoted a positive effect on microbial populations. The results indicate that the edaphic community structure and dynamics were different according to the treatments employed. CO2 evolution demonstrated no significant difference in soil microbial activity between biostimulation and bioaugmentation treatments. The total petroleum hydrocarbon (TPH) analysis indicated a biodegradation level of 35.7 and 32.2 % for the biostimulation and successive bioaugmentation treatments, respectively. Successive bioaugmentation displayed positive effects on biodegradation, with a substantial reduction in TPH levels.

Oral toxicity of Photorhabdus luminescens and Xenorhabdus nematophila (Enterobacteriaceae) against Aedes aegypti (Diptera: Culicidae).

Dengue fever is an important vector-borne disease, mainly transmitted by Aedes aegypti. To date, there are no vaccines or effective drugs available against this arboviral disease. As mosquito control is practically the only method available to control dengue fever, alternative and cost-effective pest control strategies need to be explored. The gram-negative enteric bacteria Xenorhabdus and Photorhabdus are symbiotically associated with nematode parasites, which themselves are highly pathogenic for insect larvae. Here, we evaluate the oral toxicity of these entomopathogenic bacteria in A. aegypti larvae. The susceptibility of larvae (third late or fourth early instars) was assessed by exposing them to suspensions containing Photorhabdus luminescens or Xenorhabdus nematophila, respectively. Two diet treatments were tested with larvae fed on pet food and unfed larvae. After 24 h, larvae began to die when exposed to the bacteria. Exposure to P. luminescens killed 73% of the fed and 83% of the unfed larvae, respectively. In comparison, X. nematophila was less pathogenic, killing 52% of the larvae in the fed and 42% in the unfed treatment. Remarkably, cannibalism was observed in all bioassays after exposing larvae to either of the bacterial species. To our knowledge, this is the first report demonstrating the efficiency of these entomopathogenic bacteria for oral A. aegypti killing. Our results provide a promising basis for using these bacteria as bioinsecticides for mosquito control in the future.