Enhanced biomimetic algal lipid enrichment for improved biofuel production driven by non-stress viral lysis.

Algae are promising renewable energy sources for biofuel production but remain cost-bottlenecked by lipid extraction. A low-energy solution could be provided by viral lysis by PBCV-1, a Chlorella-specific lytic virus that occurs widely in the natural environment. PBCV-1 can lyse host cells and release the intracellular lipids without using expensive sonication or chemicals. Although its capacity for disruption is documented, limited information is available on how it might rewire the host's lipidome before lysis. The objective of this study was to investigate triacylglycerol (TAG) accumulation profiles in Chlorella infected with PBCV-1. A high-resolution epifluorescence microscopy approach was employed to analyze over 4,000 cells across a full PBCV-1 lytic cycle to monitor TAG accumulation, chlorophyll fluorescence, and nuclear morphology. A multivariate unsupervised machine learning analysis revealed infection-driven asynchronous phenotypic trajectories with a 165.2 % relative increase in TAG fluorescence, contrasting with a negligible lipid gain of 5.1 % in uninfected cells. This virus-induced lipid enrichment approach has generated TAGs at levels typically achieved through nutrient deprivation, salt stress, or other synthetic or cultivation stress induction techniques. Extracellular nitrate and phosphate were further analyzed with ion chromatography under nutrient-replete conditions (NO3--N > 50 mg L-1, PO43--P > 65 mg L-1) to exclude the confounding factors of nutrient stress on lipid accumulation. The results demonstrated that PBCV-1 is a metabolic modulator and enhances TAG reserves intracellularly before facilitating their release. This study provides a novel biomimetic approach to accumulate and extract algal lipids for cost-effective biofuel production.