Effect of Carbon Source and pH on the Production and Secretion of Acid Phosphatase (EC 3.1.3.2) and Alkaline Phosphatase (EC 3.1.3.1) in Neurospora crassa

Abstract

Growth conditions (carbon source and pH of the medium) affected the level and distribution of derepressed acid and alkaline phosphatases in Neurospora crassa. Regardless of the pH, the production of both acid and alkaline phosphatases was stimulated by sucrose. Irrespective of the carbon source used, at pH values higher than 7.4 the secretion of alkaline phosphatase was stimulated, while the production and secretion of acid phosphatase was restricted. The converse was true at pH values lower than 5.7. The secretion of one of these enzymes did not exclude the simultaneous secretion of the other at pH values of around 7-0. These results suggest that the pH of the medium may play an important role in the survival of the organism in phosphorus-limited environments.

The dermatophyte Trichophyton rubrum secretes an EDTA-sensitive alkaline phosphatase on high-phosphate medium

“…The regulation of this adaptive response has proved to be highly complex, not only because of the identification of a large number of genes involved in the signaling of Pi starvation, but also because the synthesis and secretion of these enzymes are under the action of nitrogen, carbon and pH regulatory circuits (8,13,19). The pH regulatory mechanism ensures that extracellular enzymes are secreted only at pH values at which they can function effectively.…”

“…The pH regulatory mechanism ensures that extracellular enzymes are secreted only at pH values at which they can function effectively. For example, acid and alkaline Pirepressible phosphatases are secreted into the growth medium at acid and alkaline pH, respectively (14,19). However, there is increasing evidence indicating that N. crassa secretes similar amounts of the pho-2-encoded Pi-repressible APase irrespective of ambient pH when wild-type strains grow in low-Pi medium, i.e., gene pho-2, which is responsive to Pi starvation via a hierarchical regulatory circuit (20), is not an alkaline gene.…”

“…For example, the use of nucleic acids as sources of inorganic phosphate (Pi) is based on the induction of structural proteins, permeases, and enzymes of the cell wall, in addition to the secretion of a variety of proteins and hydrolytic enzymes such as nucleases and acid and alkaline phosphatases in response to both Pi starvation and environmental pH signaling. This metabolic machinery permits the fungi, and other microorganisms, to use these macromolecules as sources of essential nutrients within a broad ambient pH range (8,11,17,19). Thus, it is also important to understand the metabolic responses that govern homeostatic pH and extracellular pH sensing in dermatophytes, since the pathogenicity of many microorganisms has been demonstrated to depend on the sensing of ambient pH in the host and on the ability to adapt, which involves installation, development, and survival in the host.…”

Properties of a constitutive alkaline phosphatase from strain 74A of the mold Neurospora crassa

“…Stock cultures were maintained on slants of Vogels medium (1.6% agar) (14). Conidial suspensions (2.5 ml containing about 10 8 cells/ml) were grown for 72 h at 30 o C in an orbital shaker (160 rpm) in Erlenmeyer flasks (500 ml) containing 100 ml of high (10 mM)-Pi medium, supplemented with 44 mM of the desired carbon source as follows: non-buffered sucrose adjusted to pH 5.4, acetate buffered at pH 5.4 with 100 mM sodium maleate, non-buffered acetate adjusted to pH 7.1 and sucrose buffered with 50 mM Tris-HCl and prepared as described previously (5,15).…”

“…Only one gene encoding the Pi-repressible APase has been identified (pho-2), cloned and characterized at the molecular level (4). The pho-2 gene is a component of the phosphate acquisition system of N. crassa and is expressed irrespective of the growth pH, except that at alkaline pH the enzyme is largely secreted into the growth medium (5,6). Also, the molecular properties of the Pi-repressible APase expressed at both pH 5.4 and pH 7.8 have been extensively characterized (7)(8)(9)(10).…”