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Phycobilisomes (PBS) are antenna megacomplexes that transfer energy to photosystems II and I in thylakoids. PBS likely evolved from a basic, inefficient form into the predominant hemidiscoidal shape with radiating peripheral rods. However, it has been challenging to test this hypothesis because ancestral species are generally inaccessible. Here we use spectroscopy and cryo-electron microscopy to reveal a structure of a “paddle-shaped” PBS from a thylakoid-free cyanobacterium that likely retains ancestral traits. This PBS lacks rods and specialized ApcD and ApcF subunits, indicating relict characteristics. Other features include linkers connecting two chains of five phycocyanin hexamers (CpcN) and two core subdomains (ApcH), resulting in a paddle-shaped configuration. Energy transfer calculations demonstrate that chains are less efficient than rods. These features may nevertheless have increased light absorption by elongating PBS before multilayered thylakoids with hemidiscoidal PBS evolved. Our results provide insights into the evolution and diversification of light-harvesting strategies before the origin of thylakoids. 

Manganese dioxide (MnO 2 ) with a conversion mechanism is regarded as a promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity (∼1223 mA h g −1 ) and environmental benignity as well as low cost. However, it suffers from insufficient rate capability and poor cyclic stability. To circumvent this obstacle, semiconducting polypyrrole coated-δ-MnO 2 nanosheet arrays on nickel foam (denoted as MnO 2 @PPy/NF) are prepared via hydrothermal growth of MnO 2 followed by the electrodeposition of PPy on the anode in LIBs. The electrode with ∼50 nm thick PPy coating exhibits an outstanding overall electrochemical performance. Specifically, a high rate capability is obtained with ∼430 mA h g −1 of discharge capacity at a high current density of 2.67 A g −1 and more than 95% capacity is retained after over 120 cycles at a current rate of 0.86 A g −1 . These high electrochemical performances are attributed to the special structure which shortens the ion diffusion pathway, accelerates charge transfer, and alleviates volume change in the charging/discharging process, suggesting a promising route for designing a conversion-type anode material for LIBs.