Symbiotic chitin degradation by a novel anaerobic thermophilic bacterium Hydrogenispora sp. UUS1-1 and the bacterium Tepidanaerobacter sp. GT38

Abstract

Chitin is the second most abundant organic compound in nature. Although mesophilic bacteria degrade insoluble chitin, there is a paucity of data describing degradation of insoluble chitin by anaerobic thermophilic bacteria. In this report, we screened cow manure compost for new chitin degradation systems, and identified a chitinolytic bacterial community (CBC) that showed high chitin degradation activity under thermophilic conditions, i.e., 1% (w/v) chitin powder degraded completely within 7 days at 60 °C. Metagenomic analysis revealed that the CBC was dominated by two bacterial genera from Hydrogenispora, an uncultured taxonomic group, and Tepidanaerobacter. Hydrogenispora were abundant in the early-to-mid stages of culturing with chitin, whereas the population of Tepidanaerobacter increased during the later stages of culturing. Strains UUS1-1 and GT38, which were isolated as pure cultures using the roll-tube method with colloidal chitin, N-acetyl-d-glucosamine, and glucose as carbon sources, were found to be closely related to H. ethanolica and T. acetatoxydans, respectively. Strain UUS1−1 readily degraded chitin and is the first anaerobic thermophilic chitinolytic bacterium reported, whereas strain GT38 showed no chitinolytic activity. Based on phylogenetic analysis, UUS1−1 and GT38 should be classified as novel genera and species. Zymogram analysis revealed that UUS1−1 produces at least two chitinases with molecular weights of 150 and 40 kDa. A coculture of UUS1−1 and GT38 degraded crystalline chitin faster with lower accumulation of lactate compared with UUS1−1 alone, indicating that the strains maintained a symbiotic association through assimilation of organic acids in chitin degradation and that strain GT38 consumed end-products to reduce end-product inhibition and enhance the degradation of crystalline chitin.