English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We have described how agar provides a significant source of carbon for the growth of Aspergillus nidulans (Payton et al., 1976) and shown that the inability of acetate nonutilizing (acu) mutants to grow on agar as sole carbon source suggests that agar is utilized by the organism through the pathway of acetate metabolism (Armitt et al., 1976). We have also demonstrated that the presence of agar in test media can generate spurious growth responses ; in particular, certain acu mutants do not grow on carbon sources such as lactate, alanine, succinate, aspartate, glutamate (Payton et al., 1976) or lactamide (Payton, unpublished results) when agar is present in the medium. In contrast, the acu mutants do grow on these carbon sources when tested in liquid culture, unless the metabolic lesion in the mutant strain itself prevents growth on a particular carbon source. These results prompt us to suggest a model for the growth of A. nidulans on agar in which the degradation of the agar polymers is effected by extracellular enzyrne(s). Such a model is consistent with reports of extracellular enzymes from A. nidulans capable of degrading complex polysaccharides (Zonneveld, 19720, b). We assume that the ability of agar to inhibit the utilization of other potential carbon sources requires at least the initial degradation of the agar polymers, though the precise mechanism by which the acu mutants are prevented from utilizing the alternative carbon sources is not understood. However, since the formation of extracellular enzymes by Aspergillus is usually catabolite-repressed (Bailey & Arst, 1975 ; Cohen, 1977), it is likely that the agar-degrading enzymes are also subject to such carbon catabolite repression. Thus one might expect that the utilization of carbon sources which are strong catabolite repressors, such as glucose or sucrose, will not be susceptible to ‘agarinhibition’ due to repression of the synthesis of the enzyme(s) responsible for agar degradation. Conversely, the utilization of carbon sources which are weak catabolite repressors will exhibit ‘agar-inhibition’, that is, they will not support the growth of acu mutants when present in media solidified with agar. If the hypothesis is correct, then mutant strains selected for no growth on carbon sources which are weak catabolite repressors may in some cases be analogous to the acu mutants. In particular, we thought it possible that certain strains isolated in this laboratory (Fantes & Roberts, 1973) and elsewhere (Gajewski et al., 1972) as lactose non-utilizing mutants may not be defective in the catabolism of lactose itself but contain lesions in acetate metabolism.

Agar as a Carbon Source in Relation to the Isolation of Lactose Non-utilizing Mutants of Aspergillus nidulans