Exploring the diversity and functional profile of microbial communities of Brazilian soils with high salinity and oil contamination.

Environmental pollution associated with the petroleum industry is a major problem worldwide. Microbial degradation is extremely important whether in the extractive process or in bioremediation of contaminants. Assessing the local microbiota and its potential for degradation is crucial for implementing effective bioremediation strategies. Herein, contaminated soil samples of onshore oil fields from a semiarid region in the Northeast of Brazil were investigated using metagenomics and metataxonomics. These soils exhibited hydrocarbon contamination and high salinity indices, while a control sample was collected from an uncontaminated area. The shotgun analysis revealed the predominance of Actinomycetota and Pseudomonadota, while 16S rRNA gene amplicon analysis of the samples showed Actinomycetota, Bacillota, and Pseudomonadota as the most abundant. The Archaea domain phylotypes were assigned to Thermoproteota and Methanobacteriota. Functional analysis and metabolic profile of the soil microbiomes exhibited a broader metabolic repertoire in the uncontaminated soil, while degradation pathways and surfactant biosynthesis presented higher values in the contaminated soils, where degradation pathways of xenobiotic and aromatic compounds were also present. Biosurfactant synthetic pathways were abundant, with predominance of lipopeptides. The present work uncovers several microbial drivers of oil degradation and mechanisms of adaptation to high salinity, which are pivotal traits for sustainable soil recovery strategies.

Genome-wide analysis reveals a rhamnolipid-dependent modulation of flagellar genes in Pseudomonas aeruginosa PAO1.

Pseudomonas aeruginosa is an opportunistic pathogen and an important model organism for the study of bacterial group behaviors, including cell motility and biofilm formation. Rhamnolipids play a pivotal role in biofilm formation and motility phenotypes in P. aeruginosa, possibly acting as wetting agents and mediating chemotactic stimuli. However, no biochemical mechanism or gene regulatory network has been investigated in regard to rhamnolipids' modulation of those group behaviors. Using DNA microarrays, we investigated the transcriptomic profiles in the stationary phase of growth of wild-type P. aeruginosa PAO1 and a rhlA-mutant strain, unable to produce rhamnolipids. A total of 134 genes were differentially expressed, comprising different functional categories, indicating a significant physiological difference between the rhamnolipid-producing and -non-producing strains. Interestingly, several flagellar genes are repressed in the mutant strain, which directly relates to the inability of the rhlA-minus strain to develop a swarming-motility phenotype. Supplementation with exogenous rhamnolipids has partially restored flagellar gene expression in the mutant strain. Our results show significant evidence that rhamnolipids, the major biosynthetic products of rhlABC pathway, seem to modulate gene expression in P. aeruginosa.

Application of In-Line Mid-Infrared (MIR) Spectroscopy Coupled with Calorimetry for the Determination of the Molar Enthalpy of Reaction between Ammonium Chloride and Sodium Nitrite.

The reaction between ammonium chloride and sodium nitrite has been known for its application as a source of heat because of its large enthalpy of reaction, for which it has been used by the oil industry. There have been no known calorimetric studies for the experimental determination of its molar enthalpy of reaction, which is necessary in order to predict the limits achieved for up-scale applications. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and reaction calorimetry were used to determine this value by using a simple methodology. Both techniques were used concomitantly as a source of information regarding the time-dependent moles converted (Δn) and the amount of exchanged heat (ΔH). The molar enthalpy of reaction was calculated to be -74 ± 4 kcal mol(-1). The percentage between the confidence interval and the calculated value was 5.4%, which shows that the methodology was precise. After the determination of the molar enthalpy of reaction, it was proved that the ATR FT-IR alone was able to be used as a substitute for the reaction calorimetry technique, in which the IR signal is converted to the heat information, presenting as an easier technique for the monitoring of the heat released by this system for future applications.

Characterization of rhamnolipids produced by wild-type and engineered Burkholderia kururiensis.

Biosurfactants are a class of functional molecules produced and secreted by microorganisms, which play important roles in cell physiology such as flagellum-dependent or -independent bacterial spreading, cell signaling, and biofilm formation. They are amphipathic compounds and comprise a variety of chemical structures, including rhamnolipids, typically produced by Pseudomonas spp. and also reported within other bacterial genera. The present study is focused on Burkholderia kururiensis KP23(T), a trichloroethylene (TCE)-degrading, N-fixing, and plant growth-promoting bacterium. Herein, we describe the production of rhamnolipids by B. kururiensis, and its characterization by LTQ-Orbitrap Hybrid Mass Spectrometry, a powerful tool that allowed efficient identification of molecular subpopulations, due to its high selectivity, mass accuracy, and resolving power. The population of rhamnolipids produced by B. kururiensis revealed molecular species commonly observed in Pseudomonas spp. and/or Burkholderia spp. In addition, this strain was used as a platform for expression of two Pseudomonas aeruginosa biosynthetic enzymes: RhlA, which directly utilizes ß-hydroxydecanoyl-ACP intermediates in fatty acid synthesis to generate the HAA, and RhlB, the rhamnosyltransferase 1, which catalyzes the transfer of dTDP-L-rhamnose to ß-hydroxy fatty acids in the biosynthesis of rhamnolipids. We show that rhamnolipid production by the engineered B. kururiensis was increased over 600 % when compared to the wild type. Structural analyses demonstrated a molecular population composed mainly of monorhamnolipids, as opposed to wild-type B. kururiensis and P. aeruginosa in which dirhamnolipids are predominant. We conclude that B. kururiensis is a promising biosurfactant-producing organism, with great potential for environmental and biotechnological applications due to its non-pathogenic characteristics and efficiency as a platform for metabolic engineering and production of tailor-made biosurfactants.