Insights into the mechanisms of desiccation resistance of the Patagonian PAH-degrading strain Sphingobium sp. 22B.

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.

Diversity and antimicrobial activity of bacteria isolated from different Brazilian coral species.

Corals harbor a wide diversity of bacteria associated with their mucus. These bacteria can play an important role in nutrient cycling, degradation of xenobiotics and defense against pathogens by producing antimicrobial compounds. However, the diversity of the cultivable heterotrophic bacteria, especially in the Brazilian coral species, remains poorly understood. The present work compares the diversity of cultivable bacteria isolated from the mucus and surrounding environments of four coral species present along the Brazilian coast, and explores the antibacterial activity of these bacteria. Bacteria belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were isolated. The mucus environment presented a significantly different bacteria composition, compared to the water and sediment environments, with high abundance of Alcanivorax, Acinetobacter, Aurantimonas and Erythrobacter. No difference in the inhibition activity was found between the isolates from mucus and from the surrounding environment. Eighty-three per cent of the bacteria isolated from the mucus presented antimicrobial activity against Serratia marcescens, an opportunistic coral pathogen, suggesting that they might play a role in maintaining the health of the host. Most of the bacteria isolates that presented positive antimicrobial activity belonged to the genus Bacillus.