Ecophysiology of Alkaliphilic Anaerobes from Lake Magadi
Vadim KEVBRIN*
Institute of Microbiology, Prospect 60-let Octiabria, 7/2, 117811 Moscow, Russia
A microbial community of an alkaline Lake Magadi was investigated with the aim to describe representatives of key groups in anaerobic breakdown of organic matter. Representatives of saccharolytic, methanogenic and amino acid degrading organisms were isolated. All of them does not grow at pH 7, hence belong to true alkaliphiles. Particularly, alkaliphilic species of Spirochaeta - S. alkalica and S. africana were described (1) which develop at pHs of > 9 as anaerobic saccharolytic dissipotrophs. The products of glucose fermentations were acetate, hydrogen, ethanol, and lactate in different proportions (2).
Nitrogenous compounds are fermented by represented by the strain Z-7934. Organism ferments amino acids and some organic acids but not sugars and has no ability to hydrolyze polymeric compounds. Preferential substrates are amino acids of the ornitine cycle with arginine as the best substrate. This choice indicates to the storage nitrogenous compound of cyanobacteria, like cyanophycine, as the probable substrate for the organism in the habitat. Such limitation in metabolic type is well known for amino acids fermenting clostridia. Main products are acetate, propionate, ammonium and some hydrogen. Hence, it belongs to typical amino acid fermenters.
Strain Z-7934 is a thin rod (0.5 x 2.0 μm), non motile. Cell wall structure is of Gram-positive type. Nevertheless no sporulation was observed. It belongs to low G+C clostridial branch but even when 5 mM soluble Ca2+ was present in the medium spore formation was not.
Strain Z-7934 is mesophilic with optimal growth temperature at 37℃ and true alkaliphilic (no growth at pH 7) with optimal growth at 8.5. An organism has good growth at NaHCO3 concentration from 3% up to saturation which conforms the habitat characteristics in Lake Magadi. Strain Z-7934 is an obligate anaerobe and in spite of typical fermentative metabolism has ability to reduce DMSO to DMS and Fe(III) to Fe(II) (paper in preparation).
Sulfidogenesis is the main H2 sink in community while methanogenesis pathway was limited by methylotrophic pathway. Enrichment culture with methanol show good growth of methanogenic coccus, having 91% DNA-DNA homology with the type strain Methanosalsus zhilinaeae WeN5T (3). An interesting feature of strain Z-7936 is different pH optima on methanol and methylamines media. Thus, extremely alkaliphilic anaerobes reflect metabolic requirements in complex microbial trophic chains of Lake Magadi.
1. Zhilina, T.N., Zavarzin G.A., Rainey, E, Kevbrin, V.V., Kostrikina, N.A., and Lysenko, A.M. (1996) Int. J. Syst. Bacteriol., 46, 305-312.
2. Kevbrin, V.V., Zhilina, T.N., and Zavarzin, G.A. (1997) Microbiology, 66, 39-42.
3. Kevbrin, V.V., Lysenko, A.M., and Zhilina, T.N. (1997) Microbiology, 66, 261-266.
