Sed1p interacts with Arn3p physically and mediates ferrioxamine B uptake in Saccharomyces cerevisiae

Effect of pretreatment of hydrothermally processed rice straw with laccase-displaying yeast on ethanol fermentation

A gene encoding laccase I was identified and cloned from the white-rot fungus Trametes sp. Ha1. Laccase I contained 10 introns and an original secretion signal sequence. After laccase I without introns was prepared by overlapping polymerase chain reaction, it was inserted into expression vector pULD1 for yeast cell surface display. The oxidation activity of a laccase-I-displaying yeast as a whole-cell biocatalyst was examined with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), and the constructed yeast showed a high oxidation activity. After the pretreatment of hydrothermally processed rice straw (HPRS) with laccase-I-displaying yeast with ABTS, fermentation was conducted with yeast codisplaying endoglucanase, cellobiohydrolase, and β-glucosidase with HPRS. Fermentation of HPRS treated with laccase-I-displaying yeast was performed with 1.21-fold higher activities than those of HPRS treated with control yeast. The results indicated that pretreatment with laccase-I-displaying yeast with ABTS was effective for direct fermentation of cellulosic materials by yeast codisplaying endoglucanase, cellobiohydrolase, and β-glucosidase.

The iron- and cAMP-regulated gene SIT1 influences ferrioxamine B utilization, melanization and cell wall structure in Cryptococcus neoformans

The mechanisms by which pathogens sense and transport iron are important during infection, because of the low availability of free iron in the mammalian host. Iron is a key nutritional cue for the pathogen Cryptococcus neoformans, because it influences expression of the polysaccharide capsule that is the major virulence factor of the fungus. In this study, C. neoformans mutants were constructed with a defect in the iron-regulated gene SIT1 that encodes a putative siderophore iron transporter. Analysis of mutants in serotype A and D strains demonstrated that SIT1 is required for the use of siderophore-bound iron, and for growth in a low-iron environment. The sit1 mutants also showed changes in melanin formation and cell wall density, and it was found that mutants defective in protein kinase A, which is known to influence melanization and capsule formation, showed elevated SIT1 transcripts in both the serotype A and the serotype D backgrounds. Finally, the mutants were tested for virulence in a murine model of cryptococcosis, and it was found that SIT1 was not required for virulence. Overall, these studies establish links between iron acquisition, melanin formation and cAMP signalling in C. neoformans.

Yeast genes involved in response to lactic acid and acetic acid: acidic conditions caused by the organic acids in Saccharomyces cerevisiae cultures induce expression of intracellular metal metabolism genes regulated by Aft1p

Using two types of genome-wide analysis to investigate yeast genes involved in response to lactic acid and acetic acid, we found that the acidic condition affects metal metabolism. The first type is an expression analysis using DNA microarrays to investigate 'acid shock response' as the first step to adapt to an acidic condition, and 'acid adaptation' by maintaining integrity in the acidic condition. The other is a functional screening using the nonessential genes deletion collection of Saccharomyces cerevisiae. The expression analysis showed that genes involved in stress response, such as YGP1, TPS1 and HSP150, were induced under the acid shock response. Genes such as FIT2, ARN1 and ARN2, involved in metal metabolism regulated by Aft1p, were induced under the acid adaptation. AFT1 was induced under acid shock response and under acid adaptation with lactic acid. Moreover, green fluorescent protein-fused Aft1p was localized to the nucleus in cells grown in media containing lactic acid, acetic acid, or hydrochloric acid. Both analyses suggested that the acidic condition affects cell wall architecture. The depletion of cell-wall components encoded by SED1, DSE2, CTS1, EGT2, SCW11, SUN4 and YNL300W and histone acetyltransferase complex proteins encoded by YID21, EAF3, EAF5, EAF6 and YAF9 increased resistance to lactic acid. Depletion of the cell-wall mannoprotein Sed1p provided resistance to lactic acid, although the expression of SED1 was induced by exposure to lactic acid. Depletion of vacuolar membrane H+-ATPase and high-osmolarity glycerol mitogen-activated protein kinase proteins caused acid sensitivity. Moreover, our quantitative PCR showed that expression of PDR12 increased under acid shock response with lactic acid and decreased under acid adaptation with hydrochloric acid.

Cellular iron utilization is regulated by putative siderophore transporter FgSit1 not by free iron transporter in Fusarium graminearum

This report investigated FgSit1, which encodes a putative ferrichrome transporter of Fusarium graminearum. The identity of the deduced amino acid sequence of FgSit1 with the amino acid sequence of ScArn1p, an FC-Fe(3+) transporter of Saccharomyces cerevisiae, was 51%; both the growth defect related to the Deltafet3Deltaarn1-4 strain of S. cerevisiae in an iron-depleted condition and the FC-Fe(3+) uptake activity were recovered upon the introduction of FgSit1 into the Deltafet3Deltaarn1-4 strain. Although ScArn1p was found in the late endosomal compartment in S. cerevisiae, FgSit1 was found on the plasma membrane in S. cerevisiae; when FgSit1 was expressed exogenously in S. cerevisiae, it showed greater FC-Fe(3+) uptake activity than did ScArn1p. Additionally, in F. graminearum FC-Fe(3+) uptake activity in the Deltafgsit1 strain was found to be one-fourth that of the wild-type. However, Fe(3+) uptake activity in the Deltafgsit1 strain was 5-fold higher than that of wild-type; the gene expression of FgFtr1, a putative iron transporter, was induced by the deletion of FgSit1, but was not induced by the deletion of FgSit2. Taken together, these results strongly suggest that FgSit1 encodes a putative FC-Fe(3+) transporter that mediates FC-Fe(3+) uptake using a different mechanism than ScArn1p and plays an important role in the regulation of cellular iron availability in F. graminearum.

Functional identification of high-affinity iron permeases from Fusarium graminearum

The ScFTR1 gene encodes an iron permease in Saccharomyces cerevisiae. Its homologues, FgFtr1 and FgFtr2, were identified from filamentous pathogenic plant fungus, Fusarium graminearum. Homologies between the deduced amino acid sequences of ScFtr1p and FgFtr1 and FgFtr2 were 56 and 54%, respectively, and both had REXXE sequences, which form the conserved amino acid sequence of ScFtr1p. FgFtr1 expression increased under iron depletion, and although FgFtr2 mRNA was not detected in the wild-type strain, it was detected in the deltafgftr1 strain in the iron-depleted condition. When the FgFtr1 and FgFtr2 were deleted, the amount of growth was found not to be different from the wild-type in iron-depleted media. However, the mRNA of FgSid, a homologue of the SIDA of Aspergillus fumigatus, was dramatically increased in the deltafgftr1/deltafgftr2 strain and in an iron-depleted condition. FgFtr1 and FgFtr2 genes act as functional complements when they are introduced into the S. cerevisiae deltaScftr1 strain. The deltaScftr1 strain, which contains either the FgFtr1 or FgFtr2, grew well in iron-depleted media. Moreover, specific alteration of the REXXE consensus sequence of FgFtr1 and FgFtr2 did not allow for sustained growth of the deltaScftr1 strain on iron-depleted medium. The iron uptake activity was recovered when FgFtr1 and FgFtr2 genes were introduced into the deltaScftr1 strain. Though the Fet3p in S. cerevisiae was found on the intracellular vesicle in the deltaScftr1 strain, Fet3p was found on the plasma membrane when FgFtr1 or FgFtr2 was introduced into the deltaftr1 strain. An infection test was carried out with deletion strains; however, no change in the ability of these strains to cause disease was observed. These results suggest that FgFtr1 and FgFtr2 may function as iron permeases in the reductive iron uptake pathway and that they do not play major roles in the pathogenicity of F. graminearum.