Degradation of proteins and amino acids by Caloramator proteoclasticus in pure culture and in coculture with Methanobacterium thermoformicicum Z245 |
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Authors: | S Tarlera A J M Stams |
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Institution: | (1) Cátedra de Microbiología, Facultad de Química y Facultad de Ciencias, General Flores 2124, CC 1157, Montevideo, Uruguay e-mail: starlera@bilbo.edu.uy Tel.: +598-2924-4209 Fax: +598-2924-1906, UY;(2) Department of Microbiology, Wageningen Agricultural University, Hesselink van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands, NL |
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Abstract: | This study investigated the degradation of proteins and amino acids by Caloramator proteoclasticus, an anaerobic thermophilic (55 °C) fermentative bacterium isolated from an anaerobic bioreactor. Experiments were performed
in the presence and absence of Methanobacterium thermoformicicum Z245, a methanogen that can use both hydrogen and formate for growth. Higher production rates and yields of the principal
fermentation products from gelatin were observed in methanogenic coculture. The specific proteolytic activity in coculture
tripled the value obtained in pure culture. C. proteoclasticus fermented glutamate to acetate, formate, hydrogen and alanine. In methanogenic coculture, a shift towards higher amounts
of acetate and hydrogen with no alanine production was observed. Extracts of glutamate-grown cells possessed high activities
of β-methylaspartase, a key enzyme of the mesaconate pathway leading to acetate. The presence of two enzymes (alanine-α-ketoglutarate
aminotransferase and NADH-dependent alanine dehydrogenase) usually involved in the biosynthesis of alanine from pyruvate was
also detected. The fermentation of amino acids known to be oxidatively deaminated (leucine and valine) was improved in the
presence of both methanogenesis and glycine, a known electron acceptor in the Stickland reaction. Culture conditions seem
to be very important in the way C. proteoclasticus disposes of reducing equivalents formed during the degradation of amino acids.
Received: 29 March 1999 / Received revision: 2 July 1999 / Accepted: 1 August 1999 |
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