Central carbon metabolism switching in lytic versus temperate coral reef viral communities
Coral reefs are declining globally due in part to bacterial overgrowth, a process known as microbialization. However, the role of bacteriophages that may inhibit microbialization by infecting and killing these bacteria remains poorly understood, especially their metabolic impacts on bacterial proliferation. To address this, we analyzed central carbon metabolism gene frequencies in viral communities from healthy (lytic-dominated) and degraded (temperate-dominated) Central Pacific coral reefs. We found that viral metabolism shifted broadly from being dominated by metabolism that builds up pools of central intermediates on degraded reefs dominated by temperate viral infection ("anaplerotic" reactions) to metabolism that consumes these pools to prioritize production of metabolic precursors for virion construction on healthy reefs dominated by lytic infection ("cataplerotic" reactions). This switch was shown by the over-representation of Entner-Doudoroff (ED) glycolysis genes on degraded, temperate-dominated reefs and of pentose phosphate pathway (PPP) and reductive tricarboxylic acid cycle (TCA) genes on healthy, lytic-dominated reefs. As a result of this metabolic dichotomy, our qualitative compartment modeling revealed two distinct ecosystem states: (i) healthy reefs, where lytic viral metabolism enhances viral production and suppresses bacterial overgrowth, and (ii) degraded reefs, where temperate viral metabolism accelerates bacterial proliferation. Because viral switching between lytic and temperate lifestyles is a known function of host physiological state, these findings position viral metabolism as both a driver of reef decline and a conservation lever, with metabolically mediated "re-viralization" offering a novel strategy to restore reef resilience.