Role of homo-and heterofermentative lactic acid bacteria on hydrogen-producing reactors operated with cheese whey wastewater

•LAB survived and influenced H2 production in AFBRs fed with cheese whey.•Lactococcus spp. was the prevalent LAB in both AFBRs.•H2 yields of 1.9–2.3 mol/mol lactose were obtained in the absence of lactobacilli.•Bacteriocinogenic LAB strains were mainly found in phases with low H2 yield.

The prevalence of lactic acid bacteria (LAB) and the effects of their antimicrobial peptides on H2 production in anaerobic fluidized bed reactors (AFBRs) operated with cheese whey (AFBR1 and AFBR2) were verified in this study. The AFBR1 received 5 g COD L−1 of cheese whey with decreasing hydraulic retention times (HRT) of 14 to 8 h. The AFBR2 was operated with 3–10 g COD L−1 of cheese whey with an HRT of 6 h. Next, 152 colonies were selected from de Man, Rogosa and Sharpe MRS agar plates, and 45 strains were classified as LAB. The counts oscillated between 6.6 and 8.1 log CFU mL−1, indicating that the LAB survived and persisted in the AFBRs. Pure cultures were identified using 16S rRNA gene sequencing, and Lactococcus lactis was the prevalent LAB (70%) in both reactors. The highest H2 yields (1.9 and 2.3 mol H2 mol lactose−1) were obtained during the first operational phase in both reactors when a low organic loading rate (OLR) was applied, and when the growth of Lactococcus spp. was associated with Leuconostoc pseudomesenteroides. The bacteriocin-producing LAB (mostly Lactobacillus spp.) found on the specific phases of reactors AFBR1 and AFBR2 exerted a remarkable influence on H2 yield.