The phylogenetic diversity of Thermus and Meiothermus from microbial mats of an Australian subsurface aquifer runoff channel

Abstract

Spectral analysis of the cell free extracts of four mat samples colonizing a Great Artesian Bain (GAB) aquifer bore runoff channel suggested that Thermus was present in the 75 °C grey mat, Meiothermus was present in the 66 °C red mat, a mixed population of Meiothermus/ Thermus and photosynthetic microbes were present in the 57 °C green mat and photosynthetic microbes were present in the 52 °C brown mat. Enumeration studies indicated that Thermus dominated the grey mats and Meiothermus dominated the red mat but both were absent in samples collected at the bore source (89 °C) and below the bore source (88 °C). Culture-dependent studies followed by 16S rRNA gene sequence analysis indicated that 13 of the 14 Thermus isolates clustered closely with each other and to T. igniterrae, with the remaining strain clustering with Thermus strain SRI-96. The two Meiothermus isolates were closely related to Meiothermus ruber. A culture-independent study with 367 16S rRNA gene clones concurred that Thermus dominated the grey mat, but to a lesser extent in the red mat and the green mats and its complete absence in the brown mat. Of the four Thermus phylogroups identified one phylogroup dominated the cloned library and was related to the cluster represented by T. scotoductus. The second most dominant phylogroup was related to the cluster represented by T. igniterrae and the third and fourth phylogroups, which were the least dominant, were related to cluster represented by Thermus strain SRI-248 and T. oshima respectively. Meiothermus was only represented in the 16S rRNA gene libraries of the red, green and brown mats and formed two phylogroups, of which the most dominant was associated with the red mat and phylogenetically related to M. ruber while the second phylogroup was found only in the green mat gene library and was related to M. cerberus.