The Superiority of

(1) Background: Hyaluronic acid (HA) is a polyanionic mucopolysaccharide extensively used in biomedical and cosmetic industries due to its unique rheological properties. Recombinant HA production using other microbial platforms has received increasing interest to avoid potential toxin contamination associated with its production by streptococcal fermentation. In this study, the Gram-negative strains Escherichia coli (pLysY/Iq), E. coli Rosetta2, E. coli Rosetta (DE3) pLysS, E. coli Rosetta2 (DE3), E. coli Rosetta gammiB(DE3)pLysS, and the Gram-positive Bacillus megaterium (MS941) were investigated as new platforms for the heterologous production of HA. (2) Results: The HA biosynthesis gene hasA, cloned from Streptococcus equi subsp. zoopedemicus, was ligated into plasmid pMM1522 (MoBiTec), resulting in pMM1522 hasA, which was introduced into E. coli Rosetta-2(DE3) and B. megaterium (MS941). The initial HA titer by the two hosts in the LB medium was 5 mg/L and 50 mg/L, respectively. Streptococcal hasABC and hasABCDE genes were ligated into plasmid pPT7 (MoBiTec) and different E. coli host strains were then transformed with the resulting plasmids pPT7hasABC and pPT7hasABCDE. For E. coli Rosetta-gamiB(DE3)pLysS transformed with pPT7hasABC, HA production was 500 ± 11.4 mg/L in terrific broth (TB) medium. Productivity was slightly higher (585 ± 2.9 mg/L) when the same host was transformed with pPT7 carrying the entire HA operon. We also transformed B. megaterium (MS941) protoplasts carrying T7-RNAP with pPT7hasABC and pPT7hasABCDE. In comparison, the former plasmid resulted in HA titers of 2116.7 ± 44 and 1988.3 ± 19.6 mg/L in LB media supplemented with 5% sucrose and A5 medium + MOPSO, respectively; the latter plasmid boosted the titer final concentration further to reach 2476.7 ± 14.5 mg/L and 2350 ± 28.8 mg/L in the two media, respectively. The molecular mass of representative HA samples ranged from 105 − 106 Daltons (Da), and the polydispersity index (PDI) was <2. Fourier transform infrared spectroscopy (FTIR) spectra of the HA product were identical to those obtained for commercially available standard polymers. Finally, scanning electron microscopic examination revealed the presence of extensive HA capsules in E. coli Rosetta-gamiB(DE3)pLysS, while no HA capsules were produced by B. megaterium. (3) Conclusions: Our results suggested that Gram-positive bacteria are probably superior host strains for recombinant HA production over their Gram-negative counters. The titers and the molecular weight (MW) of HA produced by B. megaterium were significantly higher than those obtained by different E. coli host strains used in this study.