The potential of three indigenous bacterial strains (Lactobacillus delbrueckiiN2,Lactobacillus cellobiosusTM1, andLactobacillus plantarumG88) for the production of biosurfactants using sugar cane molasses or glycerol as substrates was investigated through emulsifying, surface tension, and antimicrobial activities. The different biosurfactants produced with molasses as substrate exhibited high surface tension reduction from 72 mN/m to values ranged from 47.50 ± 1.78 to 41.90 ± 0.79 mN/m and high emulsification index ranging from 49.89 ± 5.28 to 81.00 ± 1.14%. Whatever theLactobacillusstrain or the substrate used, the biosurfactants produced showed antimicrobial activities againstCandida albicansLV1, some pathogenic and/or spoilage Gram-positive and Gram-negative bacteria. The yields of biosurfactants with molasses (2.43 ± 0.09 to 3.03 ± 0.09 g/L) or glycerol (2.32 ± 0.19 to 2.82 ± 0.05 g/L) were significantly (p<0.05) high compared to those obtained with MRS broth as substrate (0.30 ± 0.02 to 0.51 ± 0.09 g/L). Preliminary characterization of crude biosurfactants reveals that they are mainly glycoproteins and glycolipids with molasses and glycerol as substrate, respectively. Therefore, sugar cane molasses or glycerol can effectively be used byLactobacillusstrains as low-cost substrates to increase their biosurfactants production.

Biosurfactants are natural surface-active compounds produced by a variety of microorganisms. The high cost of culture media limits the large-scale production and use of biosurfactants. It is therefore necessary to develop an efficient and cost-effective bioprocess to improve the yield of biosurfactants from microorganisms. In this study, the response surface method was used to optimize the production of biosurfactants by a Lactobacillus strain and the antimicrobial activity of the biosurfactants was assessed. The biosurfactant-producing strain was identified as Lactobacillus paracasei subsp. tolerans N2 after 16S rRNA gene analysis. Among the different variables studied using a Plackett–Burman statistical design, temperature and peptone and sugar cane molasses concentrations were found to be the main factors that had significant (p < 0.05) influence on biosurfactant production. The results of this study showed that molasses concentration at 59.5 g/L, peptone at 6.20 g/L and temperature of 33 °C were optimal conditions for biosurfactant production, with a maximum yield of 2.70 g/L. The biosurfactant exhibited surface tension reduction of 37.85 mN/m and antimicrobial activity expressed as inhibition diameter of 63 mm. Partial characterizations by elemental, biochemical and Fourier transmission infrared spectroscopy analysis of the biosurfactant produced revealed that it was glycolipoprotein in nature. The biosurfactant exhibited bactericidal activity against Pseudomonas aeruginosa PSB2, Pseudomonas putida PSJ1, Salmonella sp. SL2, Escherichia coli MTCC 118, Bacillus sp. BC1 and Staphylococcus aureus STP1 at concentrations ranging from 6.4 to 50 mg/mL. The yield of biosurfactant was four-fold higher after optimization of media components and culture conditions using response surface methodology. The results of this study suggested that sugar cane molasses can be used as a low-cost substrate to enhance the yield of biosurfactants with antimicrobial activity.

This study aimed to assess the antibiotic susceptibility and biofilm formation ability of pathogens isolated from braised fish as well as characterize and evaluate the antibacterial, antiadhesive, and antibiofilm activities of the biosurfactant from Lactobacillus paracasei subsp. tolerans N2 against these pathogens. The susceptibility of six pathogens isolated from braised fish (Escherichia coli EM2, Staphylococcus aureus SA1, Salmonella enteritidis PE1, Pseudomonas aeruginosa CT3, Yersinia enterolitica MH5, Proteus mirabilis MR2, and Klebsiella pneumoniae AG5) to 16 antibiotics revealed multiple resistances with an MAR index greater than 0.3. These pathogens were able to form biofilms with S. aureus SA1, which showed the highest ability. Using biochemical and elemental analyses, FTIR, GC-MS, ¹H NMR and high-resolution mass spectrometry, the biosurfactant was characterized as a novel glycolipoprotein made of two congeners of mass 482.28 and 507.27 m/z, respectively. They showed bactericidal and antiadhesive activities against all pathogens. The biosurfactant inhibited biofilm formation by these pathogens and eradicated mature biofilms.