Described herein are Schizosaccharomyces pombe yeast strains genetically engineered to produce lactic acid, wherein the best performing strains have two copies of a heterologous lactate dehydrogenase gene codon optimized for expression in S. pombe in combination with inactivation of specific alleles encoding pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) and glycerol 3 phosphate dehydrogenase (GDP). The specific alleles that are deleted are PDC201, ADH1 ADH4, and/or GDP1. The exogenous LDH genes are expressed by the S. pombe actin promoter discovered to be a constitutive high activity promoter, which may be operably linked to any gene of interest for expression in S. pombe. Also disclosed are several variant LDH genes from a variety of species that produce high levels of lactic acid when expressed in S. pombe cells.