Adaptation to salinity: Response of biogas production and microbial communities in anaerobic digestion of kitchen waste to salinity stress

Salinity stress during anaerobic digestion is known to cause extensive changes in biogas production and microbial community structure. Thus, our study sought to characterize the adaptation response of bacteria when challenged with increased salinity. Firstly, experiments were conducted at eight salinity levels at a constant kitchen waste/inoculum ratio (K/I = 1.0), which indicated that the effect of salinity on anaerobic digestion was strictly dosage-dependent. Then, kitchen waste anaerobic digestion was conducted for 70 days at five increasing salinity levels (1.0, 2.0, 4.0, 8.0, and 16.0 g NaCl/g). Furthermore, six samples taken at the end of each salinity level acclimation phase were analyzed by high-throughput sequencing, which illustrated that Euryarchaeota, Synergistetes, Firmicutes, and Bacteroidetes were dominance at phylum level. Moreover, the proportion of Methanosaeta as major genus among Euryarchaeota was 16.46% after being acclimated 70 days of NaCl acclimation, which was higher than its proportions at the initial sample (22.08%). Methanosarcina were also enriched after acclimation. Therefore, Methanosaeta and Methanosarcina could both potentially adapt to high- salinity environments. (C) 2019, The Society for Biotechnology, Japan. All rights reserved.