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Microbial communities from freshwater sediments are involved in biogeochemical cycles and they can be modified by physical and chemical changes in the environment. Linking the microbial community structure (MCS) with physicochemistry of freshwater courses allows a better understanding of its ecology and can be useful to assess the ecological impact generated by human activity. The MCS of tributary channels from La Plata River affected by oil refinery (C, D, and E) and one also by urban discharges (C) was studied. For this purpose, 16S rRNA metabarcoding analysis, in silico metagenome functional prediction, and the hydrocarbon degradation potential (in silico predictions of hydrocarbon-degrading genes and their quantification by qPCR) of the MCS were studied. Principal coordinate analysis revealed that the MCS was different between sites, and it was not structured by the hydrocarbon content. Site C showed physicochemical characteristics, bacterial taxa, and an in silico functional prediction related to fermentative/heterotrophic metabolism. Site D, despite having higher concentration of hydrocarbon, presented autotrophic, syntrophic, and methanogenic pathways commonly involved in natural processes in anoxic sediments. Site E showed and intermediate autotrophic/heterotrophic behavior. The hydrocarbon degradation potential showed no positive correlation between the hydrocarbon-degrading genes quantified and predicted. The results suggest that the hydrocarbon concentration in the sites was not enough selection pressure to structure the bacterial community composition. Understanding which is the variable that structures the bacterial community composition is essential for monitoring and designing of sustainable management strategies for contaminated freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Aim: To analyse the physiological response of Sphingobium sp. 22B to water stress. Methods and Results: The strain was grown under excess of carbon source and then subjected to low (60RH) and high (18RH) water stress conditions for 96 h. Quantification of trehalose, glycogen, polyhydroxybutyrate (PHB) and transmission electron microscopy (TEM) was studied. Genes linked with desiccation were searched in Sphingobium sp. 22B and Sphingomonas ‘sensu latu’ genomes and their transcripts were quantified by real‐time PCR. Results showed that, in the absence of water stress, strain 22B accumulated 4·76 ± 1·41% of glycogen, 0·84 ± 1·62% of trehalose and 44·9 ± 6·4% of PHB per cellular dry weight. Glycogen and trehalose were mobilized under water stressed conditions, this mobilization was significantly higher in 60RH in comparison to 18RH. Gene treY was upregulated sixfold in 60RH relative to control condition. TEM and quantification of PHB revealed that PHB was mobilized under 60RH condition accompanied by the downregulation of the phbB gene. TEM images showed an extracellular amorphous matrix in 18RH and 60RH. Major differences were found in the presence of aqpZ and trehalose genes between strain 22B and Sphingomonas genomes. Conclusion: Strain 22B showed a carbon conservative metabolism capable of accumulation of three types of endogenous carbon sources. The strain responds to water stress by changing the expression pattern of genes related to desiccation, formation of an extracellular amorphous matrix and mobilization of the carbon sources according to the degree of water stress. Trehalose, glycogen and PHB may have multiple functions in different degrees of desiccation. The robust endowment of molecular responses to desiccation shown in Sphingobium sp. 22B could explain its survival in semi‐arid soil. Significance and Impact of the Study: Understanding the physiology implicated in the toleration of the PAH‐degrading strain Sphingobium sp 22B to environmental desiccation may improve the bioaugmentation technologies in semi‐arid hydrocarbon‐contaminated soils. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the effect of autochthonous bioaugmentation (ABA) in phenanthrene-contaminated Patagonian soil microcosms, maintained under arid conditions, on phenanthrene elimination and soil microbial community. The polycyclic aromatic hydrocarbon (PAH)-degrading strain Sphingobium sp. 22B previously isolated from the Patagonian soil and selected by its resistance to drying conditions was used as inoculant. The phenanthrene concentration, dehydrogenase activity and denaturing gradient electrophoresis of 16S rRNA gene were monitored during 230 days. The results showed that when the microcosms were maintained at 20 % of soil water-holding capacity (WHC), the phenanthrene biodegradation was drastically inhibited and changes in the genetic diversity of soil microbial community were not detected, and neither the ABA nor the biostimulation managed to overcome the inhibitory effects. When the moisture was slightly increased, reached 25 % WHC, the ABA showed a significant initial stimulatory effect on phenanthrene biodegradation, demonstrating the potential of ABA in PAH bioremediation process in semiarid Patagonia. [ABSTRACT FROM AUTHOR]

The open photoacoustic cell was used to monitor the evolution rate of oxygen from tomato leaves. Estimates of the relative amount of released oxygen in vivo and in situ conditions as influenced by ambient temperature are being presented. Photorespiration phenomenon is shown to dominate above a critical temperature. The evolution of this critical point is analyzed as a function of the environmental temperature. [ABSTRACT FROM AUTHOR]