Natronocytophaga cellulosiphila, gen. nov., sp. nov., and Marinimicrobium hydrolyticum sp. nov., aerobic haloalkaliphilic bacteria of a cellulose-mineralizing consortium from soda lakes

Aerobic enrichments with three forms of insoluble cellulose at moderate salinity from soda lakes in southwestern Siberia selected a binary consortium consisting of a primary cellulolotrophic bacteroidetes and its gammaproteobacterial hemicellulolytic partner. The bacteroidetes strain ABcell3^T was separated in pure culture from colonies formed in soft agar with amorphous cellulose, while the gammaproteobacterial satellite, strain ABcell2^T, was selectively purified using glucomannan instead of cellulose. ABcell3^T was identified as a new-genus lineage in the family Cytophagaceae, and ABcell2^T formed a new species within the genus Marinimicrobium (family Cellvibrionaceae). ABcell3^T is characterized by a complex cell morphogenesis with young cells as long flexible rods with gliding motility turning into cyst-like refractive circles. It is a highly-specialized cellulotroph, growing best with various forms of native celluloses and less actively on xyloglucan and cellobiose. ABcell2^T is a motile vibrio forming yellow pigment. It has a broad-range hydrolytic potential, growing with various glucans (but not cellulose) and sugars. Its function as a saccharolytic scavenger was confirmed by a successful reconstitution of the binary consortium on cellulose. Both bacteria are aerobic, moderately salt-tolerant alkaliphiles, growing optimally at 0.4–0.8 M total Na⁺ as carbonates and pH 9.0–9.5. Functional genome analysis of strain ABcell3^T identified fourteen gene copies for potential cellulases from the GH families 5_1/5_2, 9 and 8. The genome of ABcell2^T also contains four GH9 cellulase genes but none of the others. Instead, multiple copies of different GH5 subfamilies were present with a potential hemicellulose substrate specificity. Based on phenotypic characteristics and results of phylogenomic analysis, strain ABcell3^T is proposed as a new genus and species Natronocytophaga cellulosiphila (DSM 115919 = UQM 41578), and strain ABcell2^T – as Marinimicrobium hydrolyticum sp. nov. (DSM 115774 = JCM 35976).