Impairment of ntcA gene revealed its role in regulating iron homeostasis, ROS production and cellular phenotype under iron deficiency in cyanobacterium Anabaena sp. PCC 7120

AmpR of Stenotrophomonas maltophilia is involved in stenobactin synthesis and enhanced β-lactam resistance in an iron-depleted condition

BACKGROUND

Iron is an essential nutrient for almost all aerobic organisms, including Stenotrophomonas maltophilia. Fur is the only known transcriptional regulator presumptively involved in iron homeostasis in S. maltophilia. AmpR, a LysR-type transcriptional regulator, is known to regulate β-lactamase expression and β-lactam resistance in S. maltophilia.

OBJECTIVES

To identify the novel regulator involved in controlling the viability of S. maltophilia in an iron-depleted condition and to elucidate the underlying regulatory mechanisms.

METHODS

The potential regulator involved in iron homeostasis was identified by studying the cell viabilities of different regulator mutants in 2,2'-dipyridyl (DIP)-containing medium. Iron-chelating activity was investigated using the chrome azurol S (CAS) activity assay. An iron source utilization bioassay was carried out to examine utilization of different iron sources. Gene expression was determined by quantitative real-time PCR, and the Etest method was used to evaluate antibiotic susceptibility.

RESULTS

Of the 14 tested mutants, the ampR mutant, KJΔAmpR, showed a growth compromise in DIP-containing medium. AmpR regulated stenobactin synthesis in an iron-depleted condition, but showed little involvement in the uptake and utilization of ferri-stenobactin and ferric citrate. AmpR was up-regulated by iron limitation and β-lactam challenge. S. maltophilia clinical isolates grown under conditions of iron depletion were generally more resistant to β-lactams compared with conditions of iron repletion.

CONCLUSIONS

AmpR is a dual transcriptional regulator in S. maltophilia, which regulates the β-lactam-induced β-lactamase expression and iron depletion-mediated stenobactin synthesis. AmpR is, therefore, a promising target for the development of inhibitors.

FurC (PerR) from Anabaena sp. PCC7120: a versatile transcriptional regulator engaged in the regulatory network of heterocyst development and nitrogen fixation

FurC (PerR) from Anabaena sp. PCC7120 was previously described as a key transcriptional regulator involved in setting off the oxidative stress response. In the last years, the cross-talk between oxidative stress, iron homeostasis and nitrogen metabolism is becoming more and more evident. In this work, the transcriptome of a furC-overexpressing strain was compared with that of a wild-type strain under both standard and nitrogen-deficiency conditions. The results showed that the overexpression of furC deregulates genes involved in several categories standing out photosynthesis, iron transport and nitrogen metabolism. The novel FurC-direct targets included some regulatory elements that control heterocyst development (hetZ and asr1734), genes directly involved in the heterocyst envelope formation (devBCA and hepC) and genes which participate in the nitrogen fixation process (nifHDK and nifH2, rbrA rubrerythrin and xisHI excisionase). Likewise, furC overexpression notably impacts the mRNA levels of patA encoding a key protein in the heterocyst pattern formation. The relevance of FurC in these processes is bringing out by the fact that the overexpression of furC impairs heterocyst development and cell growth under nitrogen step-down conditions. In summary, this work reveals a new player in the complex regulatory network of heterocyst formation and nitrogen fixation.

Effect of four kinds of complexing iron on the process of iron uptake by Anabaena flos-aquae

AbstractIron (Fe), which is a necessary micronutrient for algal growth, plays an important role in the physiological metabolism and enzymatic reactions of algae. This study aimed to investigate the absorption process of four kinds of complexing iron absorbed by Anabaena flos-aquae. Results showed that the absorptive capacity of A. flos-aquae to complex iron was inversely proportional to the stability of the complex bond of complex iron. Complex iron with weak binding ability can be quickly adsorbed by A. flos-aquae. The absorptive rate was as follows: ferric humate, ferric oxalate >ammonium ferric citrate >EDTA Fe. For EDTA-Fe with a strong binding ability, a moderate iron concentration (e.g. 0.6 mg l^-1) is favourable for iron uptake by A. flos-aquae. Our experiments also revealed that the process of separating iron from complex iron before entering algal cells was probably as follows: iron complexed with organic ligands were firstly adsorbed on the surface of algae cells; afterwards, iron ions were captured by organic matter on the surface of algae cells, accompanied by the rupture of the bond between Fe³⁺ and ligand; finally, the Fe³⁺ entered into the cell of algae while the organic ligands returned to the medium.

Iron deficiency influences NtcA-dependent regulation of fatty acid desaturation and heterocyte envelop formation in Anabaena sp. PCC 7120

In Anabaena sp. PCC 7120, iron is an essential trace element and its availability determines proper functioning of several kinds of metabolisms. Iron deficiency leads to several unavoidable consequences including membrane damage. In the present study, we dealt with the impact of iron deficiency on NtcA (global nitrogen regulator)-dependent regulation of two important processes, i.e. fatty acid desaturation and heterocyte envelop formation in cyanobacterium Anabaena sp. PCC 7120. In Anabaena sp. PCC 7120, NtcA regulates fatty acid desaturation by regulating enzyme fatty acid desaturases. The NtcA-based regulation of fatty acid desaturation may be direct or indirect. Furthermore, the expression of genes involved in the heterocyte envelope polysaccharide (HEP) layer formation (hepABCK) and heterocyte-specific glycolipids (HGLs) synthesis (devH, hglE_A , prpJ and devB) were also under the control of NtcA and reduced under iron deficiency background. The enhanced expression of furA and early downregulation of ntcA under iron deficiency is responsible for reduction in fatty acid desaturation as well as decrease in the expression of genes involved in HEP layer formation and HGL synthesis. Overall results confirmed that iron deficiency influences the NtcA-based regulation of fatty acid desaturation and heterocyte envelop formation in Anabaena sp. PCC 7120.