Abstract
Abundant virus-like particles were concentrated from large-volume samples from two hot springs. Both addition of viral concentrates and addition of samples induced by addition of mitomycin-C changed patterns of carbon source utilization by hot spring microbial communities. Specific effects of the two treatments depended upon both temperature and incubation period. Increased metabolic capability with greater exposure to free phages, consistent with the view that phages are major lateral transporters of metabolic genes, was observed most clearly in microbes incubated at a temperature lower than that encountered in situ. On the other hand, decreases in the diversity of utilizable C sources upon exposure to phages may have been due to lytic activity in which susceptible bacterial populations were differentially reduced by infective viruses, consistent with the “killing the winner” hypothesis. Treatment of cultures with MC-treated culture extracts, assumed to increase exposure to excised prophages, resulted in higher average metabolic rates after 18 h, but lower rates after 48 h of incubation. With incubation at in situ temperature, this same treatment led to an initial increase in the number of readily utilized C sources, followed by a decrease in community metabolic diversity relative to controls in samples from both hot springs. Thus, treatments designed to increase the interaction between hot spring microbes and either free or newly-excised phages had observable time- and temperature-dependent effects on community metabolism, demonstrating an important, yet complex, ecological role for phages in hot spring waters.
Highlights
The term phages as used here refers to bacteriophages and archaeal viruses, a subset of unicellular-organism parasites (UOPs, [1])
Interactions between phages and their heterotrophic bacterial hosts were examined in samples obtained from two eastern California (CA) hot springs: 1) a hot spring located on the shoreline of Paoha Island in Mono Lake, and 2) a spring at Little Hot Creek within the Long Valley caldera (Figure 1)
The major differences between the two sites are that Little Hot Creek (LHC) is circumneutral and low in dissolved ions, while the Paoha Island (PI) site is an alkaline hot spring, high in dissolved ions
Summary
The term phages as used here refers to bacteriophages and archaeal viruses, a subset of unicellular-organism parasites (UOPs, [1]). It is generally accepted that phages are key players in aquatic food webs and can influence bacterial diversity [2], relatively little is known regarding to what extent phages influence ecosystem function in extremely high-temperature environments such as hot springs. Recent work shows that deep-sea hydrothermal vents harbor diverse viral communities where incidences of lysogeny, and the density of temperate phages, may be quite high Phages may be of importance as vectors for genetic exchange in terrestrial hydrothermal systems, yet little is known about specific impacts of either free or temperate phage on high-temperature bacterial community metabolism. Extreme thermal tolerance is likely to be de rigeur for life forms potentially encountered beyond Earth, so it will be useful to characterize viral assemblages from environments that are thermally extreme
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