Role of Marine Fungi in the Biochemistry of the Oceans. II. Effect of Glucose, Inorganic Nitrogen, And Tris(Hydroxymethyl)Aminomethane on Growth and Ph Changes in Synthetic Media

SUMMARY

Effects of glucose, inorganic nitrogen sources, tris (hydroxymethyl) aminomethane (THAM) and initial pH on growth and pH changes by the cellulolytic marine fungi Halosphaeria mediosetigera, Culcitalna achraspora, Humicola alopallonella and Orbimyces spectabilis have been reported.

Simultaneous variation of the concentrations of glucose and NH₄NO₃ in the presence of THAM buffer caused growth maxima to occur at maximum sugar concentration but at a low NH₄NO₃ concentration. Maximum growth at increasing levels of glucose occurred at decreasing concentrations of the nitrogen sources and low pH values were produced.

Growth responses to various types of inorganic nitrogen compounds and glucose with varying amounts of THAM led to the conclusion that salts of NH₄ with strong acids were responsible for the extremely low pH values observed after growth. Organic acid production was probably not directly responsible. It was hypothesized that NH₄ cations were taken up with the consequent release of metabolic H-ions into the medium. A converse phenomenon with KNO₃ and KNO₂ in which anions were taken up, OH-ions exchanged into the medium, and the pH raised, was also demonstrated.

Growth increased as increasing amounts of THAM raised the pH above inhibitory levels. This effect was countered, however, by the toxicity of the amine at alkaline pH. THAM was considered necessary for good growth on acidogenic, inorganic nitrogen sources. All fungi utilized NH₄, NO₃ and NO₂.

With maximum amounts of glucose and NH₄NO₃, THAM concentration variation at different initial pH values showed that maximum growth was achieved by H. mediosetigera, C. achraspora and O. spectabilis at marine-like alkalinity. The toxicity of THAM at increasing concentrations and increasing pH was again demonstrated. The effect of THAM and initial pH upon final pH has been shown and optimal buffer concentrations and initial pH ranges for growth presented for each culture.

Implications of the data on the relation between the marine fungi and their environment have been noted.