Clostridiisalibacter paucivorans gen. nov., sp. nov., a novel moderately halophilic bacterium isolated from olive mill wastewater

Researchers isolated a novel bacterium, designated strain 37HS60T, from olive mill wastewater in Morocco. This strictly anaerobic, moderately halophilic bacterium exhibits unique characteristics including a Gram-positive cell wall with an atypical thick, multilayered structure. The strain grows optimally at 42°C and requires NaCl (optimum 50 g/L) for growth. Phylogenetic analysis based on 16S rRNA gene sequences places it within cluster XII of the Clostridium subphylum, with highest similarity (92.0%) to Caloranaerobacter azorensis. The organism is heterotrophic, utilizing only three organic acids (pyruvate, fumarate, and succinate) and four amino acids as energy sources, but cannot grow on sugars. Based on phenotypic and genotypic differences from related species, the authors propose strain 37HS60T as a novel genus and species: Clostridiisalibacter paucivorans (DNA G+C content 33.0 mol%). The distinctive fatty acid profile, inability to utilize common carbohydrates, and requirement for salt differentiate this organism from closely related species in the Clostridiales order.

Key findings

• A novel moderately halophilic, strictly anaerobic bacterium (Clostridiisalibacter paucivorans) was isolated from olive mill wastewater evaporation ponds in Morocco.
• The organism exhibits an atypical Gram-positive cell wall with thick, stratified multilayers and grows optimally at 42°C with 50 g/L NaCl, distinguishing it from phylogenetically related species.
• 16S rRNA gene analysis shows 92.0% similarity to Caloranaerobacter azorensis but differs significantly in cell wall structure (Gram-positive versus Gram-negative), temperature tolerance, and substrate utilization.
• The bacterium utilizes only three organic acids (pyruvate, fumarate, succinate) and four amino acids as substrates, making it oligotrophic despite being heterotrophic.
• Based on genetic (33.0 mol% G+C content) and phenotypic characteristics, strain 37HS60T represents a novel genus and species within cluster XII of the order Clostridiales.