High temperature accelerates growth of aerobic anoxygenic phototrophic bacteria in seawater

Abstract

Temperature is an important controlling factor in the growth activity of all microorganisms. Aerobic anoxygenic phototrophic (AAP) bacteria actively grow in the ocean and are known as one of the main driving forces in organic matter cycling in surface seawater environments. Whether temperature change affects AAP bacteria activity from an ecological viewpoint remains an open question. To date, no known studies have reported the effect of temperature change on AAP bacteria growth in the ocean. We here show that the growth rate of AAP bacteria exceeded that of other bacterial types at high water temperatures in the absence of grazers. The slope of the regression line of the net growth rate of AAP bacteria as a function of water temperature was the same as that for non-AAP bacteria at all temperatures (10, 20, and 30°C); however, when grazers were eliminated, it was 4.7 times higher than that of non-AAP bacteria. This result suggests that AAP bacteria are more responsive to water temperature increases than other bacteria and that AAP bacteria might become more dominant than other bacteria under elevated water temperatures.

Taxonomic differences shape the responses of freshwater aerobic anoxygenic phototrophic bacterial communities to light and predation

“…Nonetheless, due to the large size of freshwater AAP bacteria reported in these (Fauteux et al, 2015;Garcia-Chaves et al, 2016) and other lakes (Cuperová et al, 2013;Garcia-Chaves et al, 2015), and their potential preference to be attached to particles (e.g. Mašín et al, 2012), removing predators by 0.8-or 1-µm filtration as performed in previous studies (Ferrera et al, 2011;Sato-Takabe et al, 2018) could have resulted in fundamental changes in the original composition of AAP assemblages.…”

“…Regardless, all current knowledge about light and predation on natural AAP communities derives from experimental manipulations similar to those conducted in our study (Ferrera et al, 2011;Garcia-Chaves et al, 2015;Sato-Takabe et al, 2018). Our aim was thus to keep the experimental set-up as comparable as possible to those previous studies to address whether similar experimental manipulations trigger different responses when taxonomically different communities are targeted.…”

“…The hypothesis that AAP bacteria may be subjected to strong selective losses has been based on the fact that AAP bacteria are on average larger and more active than the other heterotrophic cells in bacterioplankton communities (Fauteux et al, 2015; Kirchman et al, 2014; Koblížek, 2015; Koblížek, Mašín, Ras, Poulton, & Prasil, 2007; Liu, Zhang, & Jiao, 2010; Stegman et al, 2014). To our knowledge, only three studies (two in marine sites [Ferrera et al, 2011; Sato‐Takabe et al, 2018] and one in lakes [Garcia‐Chaves et al, 2015]) have shown that AAP bacteria as a whole grow faster and are preferentially grazed compared to other prokaryotes. The finding that the identity of the PR shifters varies between lakes further suggests that not all AAP taxa are equally susceptible to predation, such that the strength of top‐down control may vary widely over time or space depending on AAP composition or on the nature of the grazer communities, which may also differ largely between such environmentally different lakes.…”

“…We acknowledge that besides reducing the encounter rates with predators, the PR treatment might also release competition for resources due to a decrease in the total number of bacteria, and thus our PR treatment probably integrates the effect of both predator reduction and release of resource competition. However, due to the large size of freshwater AAP bacteria (Cuperová, Holzer, Salka, Sommaruga, & Koblížek, 2013; Fauteux et al, 2015; Garcia‐Chaves et al, 2016) and their potential particle‐attached preference ( Mašín et al, 2012), the removal of predators by filtration through 0.8‐µm or 1‐µm pore‐size filters as performed in previous studies (Ferrera et al, 2011; Sato‐Takabe et al, 2018) could have resulted in a fundamental change in the original composition of our AAP assemblages. Moreover, the only AAP study that compared the effect of dilution (as performed in our study) with that of removing grazers through filtration showed very similar responses of AAPs in both treatments, and concluded that in the dilution treatment most of the effect was due to the release of predation pressure (Ferrera et al, 2011).…”

“…Focusing on total AAP abundance or activity, experimental manipulations have provided key insight into the environmental and biological controls of AAP in natural ecosystems. For example, AAP bacteria as a whole can be strongly grazed by flagellates in marine waters (Ferrera et al, 2011; Sato‐Takabe, Hamasaki, & Suzuki, 2018) and by protists and larger zooplankton in lakes (Garcia‐Chaves et al, 2015). Similarly, experimental light exposure has resulted in a range of bulk responses in terms of the incorporation of radioactive leucine by AAP cells from lake, estuarine or marine waters (Garcia‐Chaves, Cottrell, Kirchman, Ruiz‐González, & del Giorgio, 2016; Kirchman et al, 2014; Stegman, Cottrell, & Kirchman, 2014), and growth of marine AAP bacteria (Ferrera, Sánchez, Kolářová, Koblížek, & Gasol, 2017).…”