[P005] Poster

12:10 PM - 1:00 PM JST(3:10 AM - 4:00 AM UTC)

[P03-405] Alcohol dehydrogenase expression enables CO₂-dependent oligotrophic growth in heterotrophic bacteria

○Yuji Nagata¹, Shouta Nonoyama², Kouhei Kishida¹, Yoshiyuki Ohtsubo¹ (1. Tohoku University (Japan), 2. Institute of Science Tokyo (Japan))

Keywords:

oligotroph,CO2-fixation,sphingomonads,γ-HCH,Tn-Seq

Sphingobium japonicum strain UT26, a well-characterized γ-hexachlorocyclohexane (γ-HCH)–degrading bacterium, is a typical aerobic heterotroph that requires organic carbon sources for growth and does not proliferate on minimal salt media lacking such substrates. Here, we report that expression of an endogenous Zn-dependent alcohol dehydrogenase gene (adhX) enables UT26 to grow to a visible level under oligotrophic conditions. This phenotype, designated high-yield growth under oligotrophic conditions (HYGO), is dependent on CO₂ and is accompanied by CO₂ incorporation. Notably, the UT26 genome lacks genes encoding key enzymes of known autotrophic CO₂ fixation pathways, such as ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) and ATP-dependent citrate lyase, suggesting the involvement of a previously uncharacterized mechanism of CO₂ assimilation. Orthologues of adhX are widely distributed among sphingomonads, often located on plasmids, indicating that this phenotype may represent an adaptive strategy for survival in carbon-limited environments. Moreover, the presence of adhX-like genes in diverse bacterial taxa suggests that this mechanism may be more broadly conserved and ecologically relevant. Given the broad substrate specificity of AdhX, we hypothesize that trace alcohols present in oligotrophic environments serve as substrates for NADH generation, thereby supporting energy metabolism. To investigate the molecular basis of the HYGO phenotype, we performed qTn-Seq analysis, which identified genes involved in the glyoxylate shunt, regulatory functions, TonB-dependent transport, glycine metabolism, NAD(P) transhydrogenase, and urea carboxylation as essential. Disruption of pyruvate dehydrogenase further enhanced the phenotype. Together with RNA-Seq data, these results suggest that the HYGO phenotype is supported by metabolic reprogramming that suppresses decarboxylation via the glyoxylate shunt, promotes anaplerotic CO₂ assimilation, and utilizes trace organic compounds as energy and carbon sources. This study provides new insights into microbial metabolic flexibility under oligotrophic conditions and highlights a potential strategy for engineering bacteria capable of efficient growth in low-nutrient environments. Furthermore, the HYGO phenotype may have practical applications in environmental biotechnology, including the selective cultivation of beneficial microorganisms under nutrient-limited conditions and the suppression of unwanted microbial contamination.