No abstract

Weathering processes change properties and composition of spilled oil, representing the main reason of failure of bioaugmentation strategies. Our purpose was to investigate the metabolic adaptation of hydrocarbon-degrading bacteria at harsh conditions to be considered to overcome the limitations of bioaugmentation strategies at harsh conditions. Polluted soils, exposed for prolonged periods to weathered oil in harsh soils and weather conditions, were used. Two types of enrichment cultures were employed using 5% and 10% oil or diesel as sole carbon sources with varying the mineral nitrogen sources and C/N ratios. The most effective isolates were obtained based on growth, tolerance to toxicity, and removal efficiency of diesel hydrocarbons. Activities of the newly isolated bacteria, in relation to the microenvironment from where they were isoalted and their interaction with the weathered oil, showed individual specific ability to adapt when exposed to such factors, to acquire metabolic potentialities. Among 39 isolates, ten identified ones by 16S rDNA genes similarities, including special two Pseudomonas isolates and one Citrobacter isolate, showed particularity of shifting hydrocarbon-degrading ability from short chain n-alkanes (n-C12–n-C16) to longer chain n-alkanes (n-C21–n-C25) and vice versa by alternating nitrogen source compositions and C/N ratios. This is shown for the first time.

Dolomite (MgCa(CO 3 ) 2 ) is an important petroleum reservoir rock mineral common in ancient sedimentary rocks which is infrequently found in modern environments. The mechanism of dolomite formation remains poorly understood, although recent research has focused on the contribution of microbial processes. Sabkha is the Arabic term for saline mudflats occurring in regions characterized by extreme environmental conditions (high temperature, salinity, light intensity, and aridity), where diverse halophilic and extremophilic microorganisms are found. The dynamic evaporitic systems characteristic of sabkhas are crucial for the precipitation of minerals and a role for microorganisms in sabkhas in the process of mineralization has been proposed. In this study the Dohat Faishakh Sabkha in Qatar was investigated for evidence of the role for aerobic bacteria in mediating the formation of high magnesium carbonates and dolomite, two minerals that commonly occur in the sabkha sediments. Twenty-nine strains of aerobic microbes were obtained through inoculation on agar plates from two different cores sampled from the sabkha and identified by 16S rRNA gene sequencing as belonging to the genera Bacillus, Salinivibrio, Staphylococcus and, primarily, Virgibacillus. All strains examined caused the pH of an artificial growth medium to increase from 7 to 8.5; however, not all were capable of mediating mineral formation. Only Salinivibrio and Virgibacillus spp. isolates mediated the formation of detectable solid phases within the agar plates. Light microscopy, scanning electron microscopy energy dispersive X-ray (SEM/EDX), and X-ray diffraction (XRD) analyses indicate that the solid phase produced in the presence of these bacterial strains is MgCa(CO 3 ) 2 with a MgCO 3 mol% varying from 0 to 40%. The results of these laboratory experiments suggested that, in the Dohat Faishakh Sabkha, aerobic bacteria may contribute in the formation of very high Mg calcite, a mineral that is considered the precursor of ordered dolomite.

No abstract

No abstract

Occurrence of mineral forming and other bacteria in mats is well demonstrated.

The study of microbial communities in relation to their ecology, interaction, and genetics must be covered in Qatar with special soil, weather and water. Microorganisms of an environment never having been exposed to such factors do not have necessarily the ability to resist. However, when exposed to such factors, they are often able to adapt, that is to say the potential to acquire metabolic potentialities by recruitment vertical or horizontal specific genes, or recruitment of metabolic pathways present in the genome but not expressed. In polluted environments with oil hydrocarbons, the phenomena of horizontal/vertical transfers, mutations and adaptation to environmental stressors increase the metabolic capabilities of bacteria, including expanding their range of substrates, and allow their adaptation to new substrates. Extensive research on such fields is often focusing on genetic studies, meaning that the genes pools and expression as well as species occurrence are considered as basis. However, from the biotechnological point of view, the cell is considered, as an analogy, as factory. All its components (physical structure and the functions of the organelles and metabolic activities) are strictly regulated by regulatory machineries strictly controlled by the microenvironment. This approach will help answer the question on the different microbial communities that are available in Qatar soil and how they are unique in some biological activities. Indeed, the focus of our research is to characterize and demonstrate the diversity of biological activities within bacterial communities and strains of the same species. Here, we consider the bacterial activities related to polluting oil hydrocarbondegrading communities, including those which are biosurfactant-producers, Here, we showed that the isolation and screening strategy affected a lot, the selection of the hydrocarbon-degrading bacteria, by combining the bacterial tolerance to hydrocarbon toxicity to the hydrocarbons degradative activities. We demonstrated that several Qatari isolates are able to shift their activity from a range of hydrocarbons to another by the effect of the nitrogen source, C/N ratio and organic nitrogen source. By application of Factorial Investigation of Strains' Potentiality to Degrade Hydrocarbons, which is original in the attempt to integrate the study of the most essential nutritional elements as well as their interactions in one experimental frame, we demonstrated diversity of nutritional requirements among the same bacterial group of Pseudomonas aeruginosa strain, isolated in Qatar. Strains' response to altered growth conditions varied substantially; although they were from the same taxonomical group.

No abstract