Bacterial Physiology in the Context of Algal Partners

Marine bacteria display diverse lifestyles, many of which are shaped by close associations with microalgal partners. In the photic zone, where microalgae fix carbon through photosynthesis, bacteria consume algal-derived organic matter and often exhibit growth patterns that mirror algal activity and abundance. These interactions expose bacteria to strong fluctuations, with bursts of algal exudates during high productivity alternating with periods of scarcity. To cope, algal-associated bacteria have evolved strategies that balance rapid growth with the ability to endure starvation. This review highlights current knowledge and open questions in the physiology of algal-associated bacteria across three stages: the growth phase, supported by algal resources; the starvation phase, marked by storage strategies and a regulated decrease in cellular functions; and the transitions between these states, shaped by algal cues and corresponding bacterial responses. I hope this synthesis of our current understanding and the challenges ahead will inspire broader recognition of the importance and excitement of studying bacterial physiology in an environmental context.