Heat output by marine microbial and viral communities

Abstract

The Marine Microbial Food Web (MMFW) includes heterotrophic microbes and their protist and viral predators. These microbes consume dissolved organic matter thereby making the MMFW a major component of global biogeochemical and energy cycles. However, quantification of the MMFW contribution to these cycles is dependent on a handful of techniques, all of which require laboratory-derived conversion factors. Here we describe a differential calorimeter capable of measuring the small amounts of heat produced by marine microbes and viruses at natural populations. Using this ultra-sensitive calorimeter, we show that heat production in the presence of viruses is significantly larger than in their absence. This increased heat output occurs despite a net decrease in the number of microbes. This provides direct evidence for top-down control of microbial populations by viruses and shows that there is increased re-mineralization. A comparative statics model was developed to interpret the calorimeter measurements. The spirit of the model is thermodynamic -it restricts its view to net changes in the populations and net heat produced. The model predicts that approximately 25% of the total heat production during the growth phase of a pelagic microbial community is due directly to viral activities. This result has implications for the energy budget of our planet and for climate prediction.

Solar energy capture and transformation in the sea

“…Recently, Djamali et al (2012) have employed a purpose-built, differential microcalorimeter to measure the heat output of the marine microbial food web with an emphasis on the role of viral lysis. They experimented with aquarium-reared, size-fractionated model systems that were diluted to provide treatments with or without viruses.…”

“…Their results indicated that approximately 25% of the total heat flow in their artificial planktonic communities could be attributed to viral activities. While the claim is made that their novel instrument is capable of measuring the heat produced from open ocean assemblages of ∼ 10 5 bacterial cells ml -1 without pre-concentration (Djamali et al 2012), no such data are presented, or to my knowledge published elsewhere. Nevertheless, recent improvements in technology are very encouraging for possible use in future field studies (see review by Braissant et al 2010).…”

Viral information

“…Djamali and colleagues used isothermal calorimetry to study the heat released by marine microbial and viral communities (Djamali et al 2012). In this experiment, viruses lowered the standing stock of the cellular component by ~25 %.…”

Nanocalorimetric Characterization of Microbial Activity in Deep Subsurface Oceanic Crustal Fluids

“…An alternative approach to determining the metabolic rate of microorganisms in low-energy settings is to measure the energy dissipated by all biological activities using direct calorimetry ( Brown et al, 2004 ). This approach has been used to accurately measure the heat generated from metabolic activity in microbial cultures ( Winkelmann et al, 2004 ; Braissant et al, 2010 ) but, despite recent advances in quantifying microbial respiration rates in the environment ( Djamali et al, 2012 ; Mukhanov et al, 2012 ), technical limitations such as low sensitivities and slow responses have limited the application of calorimetry for these measurements ( Karl, 2014 ).…”