Influence of sulfide and temperature on species composition and community structure of hot spring microbial mats

Abstract

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80 degrees C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90 degrees C, and a Chloroflexus mat is formed at 65 to 70 degrees C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low-sulfide spring (1 mg liter(-1)) below 70 degrees C, whereas Aquificales were dominant in the high-sulfide spring (12 mg liter(-1)) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.

FIG. 1

Evolutionary maximum-likelihood dendrogram of the bacterial type sequences (designated SRI) detected in the sulfur mat hot spring in Iceland in the context of currently recognized bacterial divisions in the RDP. Sulfolobus acidocaldarius was used as an outgroup. The scale bar is in nucleotide substitution per sequence position.

FIG. 2

Evolutionary-distance dendrogram of the Aquificales division, showing the OTUs detected in the sulfur mat hot spring in Iceland (designated SRI) in the context of currently recognized bacterial sequences in the RDP. Thermotoga maritima was used as an outgroup. The scale bar represents 10% sequence divergence.

FIG. 3

Theoretical collector's curves for results obtained from diversity studies by using culture-independent techniques from different environments. Symbols: ■, hot spring sediment (16); ▴, sulfur mat, bacterial library (this study); ∗, sulfur mat, archaeal library (this study); ●, Chloroflexus mat (this study).