Sulphur Sources for Growth of Chlorella Fusca and Their Influence on Key Enzymes of Sulphur Metabolism

Abstract

The green alga Chlorella fusca strain 21 1-8b (algal collection of Gottingen) is able to grow on more than 100 different sulphur sources such as mercaptides, disulphides, thioethers, sulphinic and sulphonic acids including 'Good buffers', sulphoxides, sulphones and sulphate esters. This suggests that green algae might be of importance for degradation of xenobiotics and natural compounds in the overall sulphur cycle. The data presented describe the growth of C. fusca on such sulphur compounds and the influence of these compounds on enzymes of the assimilatory sulphate reduction sequence. I N T R O D U C T I O NSulphur compounds are formed, released and degraded in nature as normal constituents of the environment in a series of reactions summarized as the sulphur cycle (Zehnder & Zinder, 1980). However, man-made sulphur compounds in the form of volatiles such as SO2 and H2S or bound forms of sulphur such as catalysts, tensides, organic solvents and drugs are discharged in increasing amounts to our environment (Kellog et al., 1972). These compounds cause severe trouble not only to plants (SOz toxicity, acid rain), but possibly also to the aquatic system. The effect of anthropogenic sulphur compounds on green algae has not been studied systematically, although a survey using the cyanobacterium Synechococcus (Anacystis nidulans) has appeared (Schmidt et al., 1982). Only limited information is available about sulphur-containing substances used for growth of higher plants (Brunold & Erismann, 1975;Ellis, 1969;Hart & Filner, 1969), algae (Krauss, 1984;Saito, 1976) and cyanobacteria (Schmidt et al., 1982). Furthermore these substances could interfere with metabolic pathways such as uptake systems or regulatory signals of sulphur and nitrogen assimilation (Reuveny & Filner, 1977;Zink, 1984). This study was initiated to obtain some information on the possible value of a green alga for the detoxification of sulphur compounds of either biotic or abiotic origin. METHODSOrganism. Chlorella fusca strain 21 1-8b of the algal collection of Gottingen, FRG, was cultured on a sulphurdeficient medium (SD medium). It contained @M): KH2P04, 500; Mg(N03), .6H20, 2000; KN03, 5000; KLHPO,, 500; Ca(NO,),, 250; H$O,, 23; NazMo04.2H20, 44; Mn(N03),.6H20, 6.3; ZnCl,, 0.37; Cu(N03), .H,O, 0.16; plus 1 ml l-' of Fe-EDTA complex (8.9 g FeCI, . 4 H 2 0 and 16.7 g EDTA.2H20 dissolved in 500 ml water and aerated overnight; the filtrate was used) and 1 ml I-' of trace elements (containing, per litre, 1.43 mg H3BO3, 10 mg NaMo0,.2H20, 50 mg ZnCl, and 38 mg Cu(N0J2.2H20).The sulphur compounds of Tables 1-4 were added to a final concentration of 0-3 mM whereas the sulphur control contained 0.2 mM Na,S04. The preparation and addition of the sulphur sources is described below. Pirson flasks containing 750 ml growth medium were inoculated with 6 x lo6 cells, equivalent to about 0-002 mg chlorophyll. Cultures were grown in a Kniese apparatus at 27 "C and 14000 lx using normal air as CO, source.

Metabolism of methanesulfonic acid involves a multicomponent monooxygenase enzyme

“…Whilst the majority of research has centred on the microbial metabolism of alkylbenzene sulfonates (arySulfonates), where a common theme is the desulfonation of the aromatic ring by direct or indirect oxygenation (Locher et al ., 1991; Junker et al ., 1994; Kertesz et al ., 1994), the biodegradation of aliphatic sulfonates has been somewhat neglected. Chlorella fusca utilizes Cj-Cg primary alkylsulfonates as sole sources of sulfur (Biedlingmaier & Schmit, 1983; Krauss & Schmidt, 1987) with MSA being the least well used. Aliphatic sulfonates have also been identified as sole sulfur sources for bacteria isolated from soil and sewage (Cook & Hiitter, 1982), as well as certain enteric bacteria (Uria-Nickelsen et al ., 1993a) and some yeasts (Uria-Nickelsen et al ., 1993b).…”

“…Cblorella ftlsca utilizes C,-C, primary alkylsulfonates as sole sources of sulfur (Biedlingmaier & Schmit, 1983;Krauss & Schmidt, 1987) with MSA being the least well used. Aliphatic sulfonates have also been identified as sole sulfur sources for bacteria isolated from soil and sewage (Cook & Hutter, 1982), as well as certain enteric bacteria (Uria-Nickelsen et al, 1993a) and some yeasts (UriaNickelsen et al, 1993b).…”

Methanesulphonate utilization by a novel methylotrophic bacterium involves an unusual monooxygenase

“…The subsequent fate of MSA in the biosphere is not fully understood at present and there is little in the literature on the biodegradation of MSA. MSA was used as a sulphur source by Cblorella filsca but was the least well used of the C,-C, alkyl sulphonates tested (Biedlingmaier & Schmidt, 1983;Krauss & Schmidt, 1987). MSA has also been identified as a sulphur source for bacteria isolated from soil and sewage (Cook & Hutter, 1982) and certain enteric bacteria (Uria-Nickelsen et al, 1993).…”

Microbial Assimilation and Dissimilation of Sulfonate Sulfur

“…These compounds served as sole sulfur source for all strains examined although the final cell yield in some cases was less than that obtained with an equimolar amount of sulfate. Krauss and Schmidt (45) showed that the alga Chlorella fusca was capable of using taurine, isethionate, cysteate or other short chain sulfonates as a sulfur source, but did not use several aromatic sulfonates or longer chain buffers such as HEPES.…”