Abstract: Mutant photosynthetic organisms having reduced chlorophyll and increased photosynthetic efficiency are provided. The mutant strains have mutated or attenuated: chloroplastic SRP54 gene and SGI1 gene; chloroplastic SRP54 gene and SGI2 gene; chloroplastic SRP54 gene, SGI1, and SGI2 genes are disclosed. The mutant photosynthetic organisms exhibit increased productivity with respect to wild-type strains. Also provided are mutant photosynthetic organisms having mutated or attenuated cytosolic SRP54 genes. Provided herein are methods of producing biomass and other products such as lipids using strains having mutations in an SRP54 gene, SGI1, SGI2 genes, a combination of SGI1/SRP54, and a combination of SGI2 and SRP54 genes. Also included are constructs and methods for attenuating or disrupting SRP54, SGI1, and SGI2 genes.