Isolation and growth characterization of chlorate and/or bromate resistant mutants generated by spontaneous and induced foreword mutations at several gene loci in Aspergillus niger

Abstract

We aimed her mainly to evaluate the contribution of newly employed bromate selection system, in obtaining new Aspergillus niger nitrate/nitrite assimilation defective mutants, through Ultraviolet treatment (UV), 1, 2, 7, 8-Diepoxyoctane (DEO), phenols mixture (Phx)) and spontaneous treatments. The newly employed bromate selection system was able to specify only two putative novel mutant types designated brn (bromate resistant but chlorate sensitive (RS) strain, which may specify nitrite specific transporter) and cbrn mutants (bromate resistant and chlorate resistant strain, which may specify nitrate/nitrite bispecific system). The most relevant and innovative findings of this research work involve the isolation of the RR (cbrn) mutants (a new type of nitrate assimilation defective mutants), that could be useful for studying the bispecific nitrate /nitrite transporter system. The majority of obtained bromate resistant mutants (93.3% of the total mutants obtained by all treatments) were of the brn type, whereas the remaining percentage (6.76%) was given to cbrn strains. The highest percentages of brn mutant strains (48% and 58.6% of the total RS strains) were obtained with UA after spontaneous and Phx treatment, whereas Trp has generated 29% and 42% of RS strains after UV and DEO treatments, respectively. The obtained ratios of cbrn mutants were higher (i.e. in the range of 8.4%-11.64% of the total bromate mutants) with chemical treatments, especially when U.A or Pro was serving as sole N-sources at 25ºC rather than 37ºC. A 69% mutants` yield of Aspergillus niger mutant strains representing nine gene loci (niaD, cnx-6 loci, nrt and nirA) were selected on the bases of chlorate (600 mM) toxicity. All chlorate resistant mutants were completely sensitive to bromate (250 mM). The niaD mutants showed the highest percentage (73.97%) of chlorate resistant mutants obtained with all tested treatments. The UV treatment has generated the highest ratio (86.9%) of niaD mutants, whereas, the least (61%) was obtained with Phx treatment. The highest percentage of cnx mutants (32%) was obtained with Phx treatment. The DEO treatment as compared to other tested treatments was the best to use for obtaining the highest ratios of either nrt (13.8%) mutants or nirA (1.9%) mutants.

Plant growth-promoting activity of wild-type and bromate-resistant mutant of the endophytic fungus Colletotrichum karstii

“…In 2011, Carvalho and Costa (2011) studied the genetic variability and vegetative compatibility of nit mutant strains of C. lindemuthianum and reported, similar to the authors of current study, auxotrophic mutants for uric acid (UA). Most studies aimed at isolating Colletotrichum mutants use the chlorate resistance system, while in current assay the authors are reporting for the first time retrieval of Colletotrichum mutants through the potassium bromate resistance system (KBrO 3 ), similar to the one previously mentioned for the Aspergillus species (Kanan, 2002;Kanan & Al-Najjar, 2010). Significant statistical results were observed according to Scott-Knott test (5% significance) for the phosphate solubilizing activity of C. karstii SL5 mutant strain when compared to the wild-type strain.…”

“…Aliquots of 200 μL were plated in a Minimum Medium (MM) (1.5 g L -1 KH 2 PO 4 , 0.5 g L -1 KCl, 0.5 g L -1 MgSO 4 .7H 2 O, 0.001 g L -1 FeSO 4 , 0.001 g L -1 ZnSO 4 , 10 g L -1 Glucose, 15 g L -1 Agar, 1000 mL distilled water; pH 6.8) containing potassium bromate (25 mM) with a single source of N (5 mM). All plates were cultured for 48h at 28ºC (Kanan & Al-Najjar, 2010).…”

“…Another alternative is the isolation and identification of spontaneous or induced mutant strains, which maximize or introduce characteristics of biotechnological interest. For filamentous fungi, chlorate (KClO 3 ) and potassium bromate (KBrO 3 ) resistance systems are the most commonly described, especially the nit auxotrophic mutants (Kanan, 2002;Prado et al, 2007;Rosada et al, 2010;Kanan & Al-Najjar, 2010).…”