Deletion of the N-terminal region of the AREA protein is correlated with a derepressed phenotype with respect to nitrogen metabolite repression

Genomic, morphological, and biochemical analyses of a multi-metal resistant but multi-drug susceptible strain of Bordetella petrii from hospital soil

Contamination of soil by antibiotics and heavy metals originating from hospital facilities has emerged as a major cause for the development of resistant microbes. We collected soil samples surrounding a hospital effluent and measured the resistance of bacterial isolates against multiple antibiotics and heavy metals. One strain BMCSI 3 was found to be sensitive to all tested antibiotics. However, it was resistant to many heavy metals and metalloids like cadmium, chromium, copper, mercury, arsenic, and others. This strain was motile and potentially spore-forming. Whole-genome shotgun assembly of BMCSI 3 produced 4.95 Mb genome with 4,638 protein-coding genes. The taxonomic and phylogenetic analysis revealed it, to be a Bordetella petrii strain. Multiple genomic islands carrying mobile genetic elements; coding for heavy metal resistant genes, response regulators or transcription factors, transporters, and multi-drug efflux pumps were identified from the genome. A comparative genomic analysis of BMCSI 3 with annotated genomes of other free-living B. petrii revealed the presence of multiple transposable elements and several genes involved in stress response and metabolism. This study provides insights into how genomic reorganization and plasticity results in evolution of heavy metals resistance by acquiring genes from its natural environment.

Characterization of an Nmr homolog that modulates GATA factor-mediated nitrogen metabolite repression in Cryptococcus neoformans

Nitrogen source utilization plays a critical role in fungal development, secondary metabolite production and pathogenesis. In both the Ascomycota and Basidiomycota, GATA transcription factors globally activate the expression of catabolic enzyme-encoding genes required to degrade complex nitrogenous compounds. However, in the presence of preferred nitrogen sources such as ammonium, GATA factor activity is inhibited in some species through interaction with co-repressor Nmr proteins. This regulatory phenomenon, nitrogen metabolite repression, enables preferential utilization of readily assimilated nitrogen sources. In the basidiomycete pathogen Cryptococcus neoformans, the GATA factor Gat1/Are1 has been co-opted into regulating multiple key virulence traits in addition to nitrogen catabolism. Here, we further characterize Gat1/Are1 function and investigate the regulatory role of the predicted Nmr homolog Tar1. While GAT1/ARE1 expression is induced during nitrogen limitation, TAR1 transcription is unaffected by nitrogen availability. Deletion of TAR1 leads to inappropriate derepression of non-preferred nitrogen catabolic pathways in the simultaneous presence of favoured sources. In addition to exhibiting its evolutionary conserved role of inhibiting GATA factor activity under repressing conditions, Tar1 also positively regulates GAT1/ARE1 transcription under non-repressing conditions. The molecular mechanism by which Tar1 modulates nitrogen metabolite repression, however, remains open to speculation. Interaction between Tar1 and Gat1/Are1 was undetectable in a yeast two-hybrid assay, consistent with Tar1 and Gat1/Are1 each lacking the conserved C-terminus regions present in ascomycete Nmr proteins and GATA factors that are known to interact with each other. Importantly, both Tar1 and Gat1/Are1 are suppressors of C. neoformans virulence, reiterating and highlighting the paradigm of nitrogen regulation of pathogenesis.

Transcriptional control ofnmrAby the bZIP transcription factor MeaB reveals a new level of nitrogen regulation inAspergillus nidulans

Fungi can use a diverse range of nitrogen sources. Some nitrogen sources sustain a rapid growth rate and are used in preference to less readily metabolized nitrogen sources. The mechanisms involved in this control of nitrogen utilization have been studied in the model filamentous ascomycete, Aspergillus nidulans. The GATA transcription factor AreA is necessary for the expression of nitrogen-catabolic permeases and enzymes. AreA activity is controlled by multiple mechanisms including regulated areA transcript levels and regulated AreA nuclear export. During nitrogen sufficiency, AreA activation is also prevented by the co-repressor NmrA. We have investigated nitrogen signalling to NmrA. NmrA overexpression prevents AreA function irrespective of the nitrogen status. The mRNA levels of areA and nmrA are inversely regulated, suggesting that the relative levels of AreA and NmrA are critical in determining AreA activation. The bZIP transcription factor MeaB was found to activate nmrA expression and a conserved element, TTGCACCAT, bound by MeaB in vitro is present in the promoters of NmrA homologues in other filamentous ascomycetes. Expression of meaB was not strongly regulated suggesting that transcriptional activation by MeaB is modulated by the nitrogen status. This work highlights a new level of complexity in the regulation of nitrogen catabolism.

Hansenula polymorpha NMR2 and NMR4, two new loci involved in nitrogen metabolite repression

In the yeast Hansenula polymorpha (Pichia angusta) nitrate assimilation is tightly regulated and subject to a dual control: nitrogen metabolite repression (NMR), triggered by reduced nitrogen compounds, and induction, elicited by nitrate itself. In a previous paper [Serrani, F., Rossi, B. and Berardi, E (2001) Nitrogen metabolite repression in Hansenula polymorpha: the nmrl-l mutation. Curr. Genet. 40, 243-250], we identified five loci (NMR1-NMR5) involved in NMR, and characterised one of them (NMR1), which likely identifies a regulatory factor. Here, we describe two more mutants, namely nmr2-1 and nmr4-1. The first one possibly identifies a regulatory factor involved in nitrogen metabolite repression by various nitrogen sources alternative to ammonium. The second one, apparently involved in ammonium assimilation, probably has sensor functions.

Deletion of the 389 N-terminal residues of the transcriptional activator AREA does not result in nitrogen metabolite derepression in Aspergillus nidulans

Utilizing a homologous gene replacement in order to retain the native promoter and 5' and 3' untranslated messenger regions (and thereby ensure physiological validity), we have shown that deletion of the N-terminal 389 amino acids of the transcriptional activator AREA does not result in nitrogen metabolite derepression in Aspergillus nidulans. Our results provide no evidence for a modulating interaction involving the N terminus of AREA and contrast with those of H. K. Lamb, A. L. Dodds, D. R. Swatman, E. Cairns, and A. R. Hawkins (J. Bacteriol. 179:6649-6656, 1997), who used nontargeted ectopic copies of a construct containing a heterologous promoter and untranslated regions. Results obtained with this deletion mutant, nevertheless, provide further evidence for the dispensability of large portions of AREA.