Solid-state fermentation of pristinamycin by Streptomyces pristinaespiralis NRRL ISP-5338 using D-optimal design.

Pristinamycin (PST), produced by Streptomyces pristinaespiralis NRRL ISP-5338, is a streptogramin antibiotic with remarkably broad-spectrum bactericidal activity. The production of PST from its natural producer remains challenging. In the literature, a few reports examined PST production using submerged liquid fermentation (SLF). However, the literature survey revealed no reports that studied its production using solid-state fermentation (SSF). To our knowledge, this is the first report about the production optimization of PST using SSF. Therefore, in this study, we aimed to optimize various nutritional and environmental factors influencing its production as one-factor-at-a-time (OFAT) or as a multifactorial response surface method (RSM) using SSF. Three factors, including types of solid substrates, composition of the moistening broth, and incubation time, were optimized as OFAT. The OFAT optimal conditions were wheat bran as a solid substrate, IPS5 as a moistening broth, and 9 days as incubation time. These conditions increased PST production from 0.395 to 0.467 mg/g initial dry substrate (IDS). Using RSM, three factors--the initial pH of the moistening broth, the incubation temperature, and the inoculum size (v/w)--were statistically optimized, and the model was statistically significant with a p-value < 0.05. It resulted in a 2.3-fold increase in PST production (0.910 mg/g IDS) compared to the unoptimized SSF conditions (0.395 mg/g IDS) and a 5.35-fold increase from that obtained by the SLF (0.170 mg /mL). In conclusion, the SSF is an efficient and simple method for PST production, and the optimized conditions are highly recommended for scaling up.