Protistan grazing and viral lysis losses of bacterial carbon production in a large mesotrophic lake (Lake Biwa)

Abstract

The grazing and lysis mortality of planktonic bacteria were estimated using the modified dilution method and respiratory quinone (RQ) analysis in mesotrophic Lake Biwa, Japan. The planktonic bacterial assemblages in the lake consisted of various RQs subgroups with different growth and mortality rates. The sum of total bacterial mortalities due to protistan grazing and viral lysis accounted for 96.6% (range; 89.0-107.2%) of daily total bacterial production. This is the first report which successfully demonstrates a balanced relationship between bacterial production and losses using the modified dilution method in a lake. The growth rates of ubiquinone (UQ)-containing bacteria were faster than those of menaquinone-containing bacteria. Especially, the dominant and fastest-growing bacterial groups in the present study were the bacterial groups containing UQ-8 or UQ-10. The sum of their production and loss accounted for 60% of carbon fluxes within the microbial loop. Thus, a large portion of the carbon cycling through the bacterial community in Lake Biwa can be explained by the carbon fluxes through dominant bacterial groups.

Growth and mortality rates of prokaryotes in the hypolimnion of a deep freshwater lake (Lake Biwa, Japan)

“…Positive relationships between viral lysis and host growth have been reported for both bacteria (Weinbauer et al 2003) and Synechococcus (Pasulka et al 2015). We also found the positive relationships between viral lysis and bacterial growth in the epilimnion of Lake Biwa (Takasu et al 2014). In the present study, however, viral lysis remained low in the hypolimnion.…”

“…Despite low viral lytic pressure on prokaryotes, the range of virus-to-prokaryote abundance ratios (VPRs) were 11.9-28.5 in the hypolimnion, falling within the range of the epilimnion (Takasu et al 2014). In addition to host abundance and growth rate, factors that decrease the viral population may also account for the observed VPR, since viral populations are determined by both viral production and decay.…”

Precipitous Increase of Bacterial CRISPR-Cas Abundance at Around 45°C

“…Bacterial communities are often heavily consumed by eukaryotic predators ( Jousset, 2012 ). In freshwater and marine environments, viral lysis and predation by ciliated and flagellated protists contributed to most bacterial mortality ( Pernthaler, 2005 ; Takasu et al, 2014 ). In addition, some bacteria could also kill other bacteria and consume the released nutrients.…”

Bacterial CRISPR-Cas Abundance Increases Precipitously at Around 45°C: Linking Antivirus Immunity to Grazing Risk

“…Most of the bacterial mortality is caused by cellular predator grazing and viral lysis. 37 For picophytoplankton, grazer-mediated mortality and viral-mediated mortality are inversely correlated. 38, 39 Indirect interactions among grazers and viruses are destined to occur provided that bacterial cells have tradeoffs in the grazing resistance and virus resistance.…”

“…When the hosts are exposed to lethal predators, the priority to invest in the immune function would be reduced. Most of the bacterial mortality is caused by cellular predator grazing and viral lysis (23). When bacterial mortality mostly comes from predator grazing, allocating the limiting resources to the adaptive immunity does not have priority.…”