Artificial cold-adapted microbial mats cultured from Antarctic lake samples. 1. Formation and structure

Abstract

Artificial microbial mats were cultured at 4 to 7°C in benthic gradient chambers using inocula of Antarctic lake mats (Lake Fryxell, Dry Valleys). Their formation and structure were studied based on both HPLC pigment quantification and microsensor measurements of oxygen profiles. Accretion rates (2 to 5 mm within the year) were consistent with previous estimations for artificial mats cultured at 17 to 25°C, suggesting that the microbial community was cold-adapted. Mats were vertically structured comprising an upper green layer dominated by cyanobacteria and an underlying pink layer including purple non-sulphur phototrophic bacteria. Pigment contents indicated that both groups of cyanobacteria (Oscillatoriacae and possibly Nostoc sp.) adopted different patterns of vertical distributions within the mats. Heterogeneity of oxygen vertical distributions was determined, and net primary productivity rates were in the range of those previously reported for natural Antarctic microbial mats. Collective considerations of pigment contents and primary productivity strongly suggest that artificial mats presented some characteristics of natural polar mats, although some differences were established. KEY WORDS: Antarctica · Artificial mats · Psychroptrophs · Pigments · HPLC · Net productivityResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 26: 115-125, 2001 from Antarctic meltwater ponds have been characterised; however, little is known about cold-adaptation processes in Antarctic mats (Nadeau & Castenholz 2000). Experimental works on Antarctic microbial mats may be partly complicated by difficulties encountered in preserving Antarctic mats without disturbing them over the long periods of time that are usually required for bringing samples from the field to the laboratory. Fenchel (1998a,b,c) has shown that artificial microbial mats from temperate environments can be obtained by experimental culturing using inocula of defaunated sediments. Further, the structure of these artificial mats was comparable to those of natural microbial mats, demonstrating the potential of this approach . Accordingly, the purpose of this study was to culture microbial mats initiated with Antarctic lake samples, at low temperature and under conditions mimicking field conditions. For that purpose, we used benthic gradient chambers (BGC). These devices have been previously designed to culture phototrophic microorganisms under physicochemical conditions occurring at the sediment-water interface (Pringault et al. 1996, Pringault & Garcia-Pichel 2000. The present paper describes the formation, the growth and the structure of artificial 'cold-mats' based on both pigment quantification and oxygen distribution. Part 2 (Pringault et al. 2001, this issue) reports the short-term temperature effects on oxygen turnover in these artificial cold-adapted mats. MATERIALS AND METHODSSite and sampling. Lake Fryxell (75°36' S, 163°35' E) is located in the Taylor Valley of the Dry Valley region, western Antarct...

Cyanobacterial Diversity in Natural and Artificial Microbial Mats of Lake Fryxell (McMurdo Dry Valleys, Antarctica): a Morphological and Molecular Approach

“…The apparent absence of heterocystous taxa was also reflected by the scytonemin contents, which were 2 orders of magnitudes lower in the BGC mat than in the field mat. Scytonemin plays an important role in photoprotection against the deleterious effects of UV radiation in Antarctic mats (21) but does not provide a real advantage under culture conditions where artificial light is less harmful (11). This may suggest that members of the Nostocales were overgrown by fast-growing oscillatorians.…”

“…In terms of pigment content and primary productivity, Buffan-Dubau et al (11) have suggested that artificial mats have some characteristics of natural polar mats, although some differences were found.…”

“…Our analysis of the cyanobacterial diversity in a field mat sample from Lake Fryxell was enlarged to include a derived cultured mat from a BGC, since the BGC mat has been extensively studied by using microsensor techniques and pigment analysis (11,43), which permit linkage of its community structure directly to its functional properties.…”

“…An artificial microbial mat was cultured in a BGC with opposing oxygen and sulfide gradients at 5°C for 8.5 months at the University of Bordeaux. Further details of the cultivation procedure and a structural description of the mat have been provided by Buffan-Dubau et al (11). The artificial mat grew mainly above the sand surface and reached a final thickness of 2.5 to 5 mm.…”

“…The same mat sample was shared by the different research groups and was used for determinations of bacterial and archaeal diversity (8,59,61), as well as an inoculum for culturing mat communities with a benthic gradient chamber (BGC) (11). The artificial communities cultured in the BGC at 5°C were clearly cold adapted, as oxygenic photosynthesis was optimal at 10°C, and they shared several features with the field mat, such as pinnacle formation and pigment composition (11,43).…”