A copper-responsive gene cluster is required for copper homeostasis and contributes to oxidative resistance in Deinococcus radiodurans R1

The Influence of Copper Homeostasis Genes copA and copB on Xylella fastidiosa Virulence Is Affected by Sap Copper Concentration

Xylella fastidiosa is a xylem-limited plant pathogenic bacterium that causes diseases worldwide in crops such as grape, citrus, and olive. Although copper (Cu)-containing compounds are not used for management of X. fastidiosa-caused diseases, they are widely used in X. fastidiosa hosts in vineyards and orchards. The accumulation of Cu in soils and, therefore, plant saps, could be a challenge for X. fastidiosa survival. Here, the molecular basis of Cu homeostasis was studied in relation to virulence. Although homologous Cu-related genes copA (X. fastidiosa loci PD0100) and copB (PD0101) have been characterized in other bacteria, their functions differ among bacterial species. In vitro, both copA and copB mutants were more sensitive to Cu than the wild-type (WT) strain. Interestingly, the copA mutant was more sensitive to Cu shock, while the copB mutant was more sensitive to chronic Cu treatments. In tobacco greenhouse experiments with normal watering, both mutants reduced virulence compared with WT. But when Cu was added as a drench treatment, both copA and copB mutants had increased disease severity approximately 20 and 50% compared with mutants without Cu added, respectively, which were significantly higher than the approximately 5% observed for WT under the same conditions. These results indicate that the pathogen's Cu homeostasis affects virulence and is influenced by Cu concentration in the environment. Understanding Cu homeostasis in X. fastidiosa will help discern the outcome of Cu treatments and the adaptation of this pathogen to the xylem of plants that have been exposed to high Cu concentrations because of agricultural practices.

Effect of copper sulfate on the external microbiota of adult common snook (Centropomus undecimalis)

BACKGROUND

The environment exerts a strong influence on the fish external microbiota, with lower diversity and increased abundances of opportunistic bacterial groups characterizing cultured fish compared to their wild counterparts. Deviation from a healthy external microbiota structure has been associated with increased susceptibility to bacterial pathogens. Treatment of wild-caught broodstock with copper sulfate for the removal of external parasites is a common aquaculture practice. Despite the microbiota's importance to fish health, the effects of copper sulfate on mucosal bacterial communities and their ability to recover following this chemical treatment have not been examined. The skin microbiota of adult common snook was characterized from wild individuals (Wild), and wild-caught fish maintained in recirculating aquaculture systems (RAS) immediately following a month-long copper sulfate treatment (Captive-1), and then two-weeks (Captive-2) and 2 years (Captive-3) after cessation of copper treatment.

RESULTS

The skin microbiota of wild fish were characterized by high diversity and taxa including Synechocococcus, SAR11, and a member of the Roseobacter clade. Bacterial diversity decreased in Captive individuals during the 2-year sampling period. Captive fish harbored greater abundances of Firmicutes, which may reflect glycan differences between aquaculture and natural feeds. Bacterial taxa with copper resistance mechanisms and indicative of metal contamination were enriched in Captive-1 and Captive-2 fish. Vibrionaceae were dominant in Captive fish, particularly immediately and 2 weeks following copper treatment. Based on our observations and previous literature, our results suggest putatively beneficial taxa amass over time in captivity. Within 2 years, Captive individuals harbored Bacillus which contains numerous probiotic candidates and the complex carbon degraders of the family Saprospiraceae. Predicted butanoate metabolism exceeded that of Wild fish, and its reported roles in immunity and energy provision suggest a prebiotic effect for fishes.

CONCLUSIONS

The mucosal microbiota contains bacterial taxa that may act as bioindicators of environmental pollution. Increases in mutualistic groups indicate a return to a beneficial skin microbiota following copper sulfate treatment. Our data also suggests that vastly different taxa, influenced by environmental conditions, can be associated with adult fish without noticeable health impairment, perhaps due to establishment of various mutualists to maintain fish mucosal health.

A Genome-Wide Search for Ionizing-Radiation-Responsive Elements in Deinococcus radiodurans Reveals a Regulatory Role for the DNA Gyrase Subunit A Gene's 5' Untranslated Region in the Radiation and Desiccation Response

Tight regulation of gene expression is important for the survival of Deinococcus radiodurans, a model bacterium of extreme stress resistance. Few studies have examined the use of regulatory RNAs as a possible contributing mechanism to ionizing radiation (IR) resistance, despite their proffered efficient and dynamic gene expression regulation under IR stress. This work presents a transcriptome-based approach for the identification of stress-responsive regulatory 5' untranslated region (5'-UTR) elements in D. radiodurans R1 that can be broadly applied to other bacteria. Using this platform and an in vivo fluorescence screen, we uncovered the presence of a radiation-responsive regulatory motif in the 5' UTR of the DNA gyrase subunit A gene. Additional screens under H2O2-induced oxidative stress revealed the specificity of the response of this element to IR stress. Further examination of the sequence revealed a regulatory motif of the radiation and desiccation response (RDR) in the 5' UTR that is necessary for the recovery of D. radiodurans from high doses of IR. Furthermore, we suggest that it is the preservation of predicted RNA structure, in addition to DNA sequence consensus of the motif, that permits this important regulatory ability.IMPORTANCEDeinococcus radiodurans is an extremely stress-resistant bacterium capable of tolerating up to 3,000 times more ionizing radiation than human cells. As an integral part of the stress response mechanism of this organism, we suspect that it maintains stringent control of gene expression. However, understanding of its regulatory pathways remains incomplete to date. Untranslated RNA elements have been demonstrated to play crucial roles in gene regulation throughout bacteria. In this work, we focus on searching for and characterizing responsive RNA elements under radiation stress and propose that multiple levels of gene regulation work simultaneously to enable this organism to efficiently recover from exposure to ionizing radiation. The model we propose serves as a generic template to investigate similar mechanisms of gene regulation under stress that have likely evolved in other bacterial species.

Mechanisms of Stress Resistance and Gene Regulation in the Radioresistant Bacterium Deinococcus radiodurans

The bacterium Deinococcus radiodurans reveals extraordinary resistance to ionizing radiation, oxidative stress, desiccation, and other damaging conditions. In this review, we consider the main molecular mechanisms underlying such resistance, including the action of specific DNA repair and antioxidation systems, and transcription regulation during the anti-stress response.

A comparison between ultraviolet disinfection and copper alginate beads within a vortex bioreactor for the deactivation of bacteria in simulated waste streams with high levels of colour, humic acid and suspended solids

We show in this study that the combination of a swirl flow reactor and an antimicrobial agent (in this case copper alginate beads) is a promising technique for the remediation of contaminated water in waste streams recalcitrant to UV-C treatment. This is demonstrated by comparing the viability of both common and UV-C resistant organisms in operating conditions where UV-C proves ineffective - notably high levels of solids and compounds which deflect UV-C. The swirl flow reactor is easy to construct from commonly available plumbing parts and may prove a versatile and powerful tool in waste water treatment in developing countries.