Characterization and antimicrobial activity of lactic acid bacteria from fermentative bioreactors during hydrogen production using cassava processing wastewater

• Hydrogen production anaerobic fluidized bed reactors from cassava wastewater.
• 2.0 mmol H2 g−1 COD and 2.1 L H2 d−1 L−1 were produced.
• Elevated counts of LAB were found in the effluent samples.
• The LAB community were similar to Lactobacillus sp. and Lactococcus lactis.

Fermentative hydrogen production was evaluated using two anaerobic fluidized bed reactors (AFBRs). The reactors were fed cassava processing wastewater and operated with varying organic loading rates (OLR: 4–30 kg COD m−3 d−1) for up to 160 d under mesophilic conditions. The effects and roles of lactic acid bacteria (LAB) and their antimicrobial peptides in hydrogen-producing bioreactors and on hydrogen producers were evaluated. A maximum hydrogen yield of 2.0 mmol g−1 COD and a maximum hydrogen production rate of 2.1 L H2 d−1 L−1 were achieved with OLRs of 10 kg COD m−3 d−1 and 14 kg COD m−3 d−1, respectively, which coincided with the absence of bacteriocin-producing lactic acid bacteria. The major metabolites were lactic acid, ethanol, methanol, acetic acid and butyric acid. After growth on MRS agar, gram-staining and catalase tests, 47 strains were classified as presumptive lactic acid bacteria, with counts ranging from <10 to 1.5 × 109 CFU mL−1 for both reactors, providing evidence that lactic acid bacteria are able to survive and persist in the reactors. Thirty-nine pure cultures of the LAB community were successfully identified by 16S rRNA sequencing. For AFBR1 (4–12 kg COD m−3 d−1), there was a prevalence of Lactobacillus sp. (45.4%), followed by Lactococcus lactis (31.8%). Lactobacillus sp. (78.6%) was the prevalent genus for AFBR2 (14–30 kg COD m−3 d−1).