Additional information available on CD in the print copy held at the University of Leicester Library.The microbial ecology of hot springs in Rehai geothermal field in Yunnan Province, China and salt lakes in Inner Mongolia, China were investigated. 16S ribosomal RNA (rRNA) genes were amplified from these environments and were cloned and sequenced. This molecular analysis showed that the 72.1'C hot spring contained Aquificae-dominated white streamers, while the hot water discharge (60 - 65*C) contained a laminated mat. This analysis also showed that the salt lakes were dominated by Halorubrum (34% of clone sequences). \ud The salt lakes' bacterial community consisted of Gammaproteobacteria(2 0%), Finnicutes (20%) and Bacteroidetes (20%), though the bacterium Salinibacter ruber appeared to be the predominant bacterium in the saltern at Lake Ejinnor. Moreover, several Gammaproteobacteria (67% of bacterial isolates) and Firmicutes (23%) and a few Archaea (Halorubrum and Haloarcula sp.) were cultivated from the salt lakes; the majority of isolates retrieved were not detected by molecular analysis. Statistical analysis showed that temperature, Na and Mg ions, and pH were the factors that drive microbial community composition in the salt lakes, and that geographic distance is not a factor, hence the hypothesis that 'the milieu selects' can be applicable. Furthermore, the archaeal community consists of closely related lineages, whereas the bacterial community is highly diverse.\ud Two novel archaeal viruses that infect a haloarchaeal strain that is 98% identical to Halontbrian saccharovorum1 6S rRNA sequencew ere isolated from salt lake water of Lake Bagaejinnor. Both are lytic head/tailed viruses; virus BJ1 is assigned to the Siphoviridae, while virus BJ2 is assigned to the Myoviridae, both of the order Caudovirales. Virus BJI has a 42271 base pair (bp) double stranded (ds) DNA genome, with a G+C content of 64.8 mol%\ud that is terminally redundant and may be circularly permuted. Almost all Open Reading Frames (ORFs) are in the forward strand in the same direction consistent with a rolling circle mechanism of DNA replication. A fraction of the virus population contained extra DNA that is probably host derived, and may suggest viral integration. Virus BJ2 genome is linear dsDNA. It is incomplete, but 97602 bp (approximately 90% of the genome) has been sequenced which has a G+C content of 51 mol% in 42 contigs. No genomici dentity between the viruses has been observed. Virus BJ2 has a narrow host range; it is unable to infect the type strain of Halorubrum saccharovorum or closely related field isolates. Virus BJ2 is stable from 4*C to 50'C, but titres drop ten fold at 60'C. Maximal titres were observed at 2 to 3M NaCl and titres were stable at pH 6- 10, but reduced 10000 fold at pH 4
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