Natronorubrum daqingense JX313^T is an extremely halophilic archaea that can grow in a NaCl-saturated environment. The excellent salt tolerance of N. daqingense makes it a high-potential candidate for researching the salt stress mechanisms of halophilic microorganisms from Natronorubrum. In this study, transcriptome analysis revealed that three genes related to the biosynthesis of vitamin B₁₂ were upregulated in response to salt stress. For the wild-type (WT) strain JX313^T, the low-salt adaptive mutant LND5, and the vitamin B₁₂ synthesis-deficient strain ΔcobC, the exogenous addition of 10 mg/L of vitamin B₁₂ could maximize their cell survival and biomass in both optimal and salt stress environments. Knockout of cobC resulted in changes in the growth boundary of the strain, as well as a significant decrease in cell survival and biomass, and the inability to synthesize vitamin B₁₂. According to the HPLC analysis, when the external NaCl concentration (w/v) increased from 17.5% (optimal) to 22.5% (5% salt stress), the intracellular accumulation of vitamin B₁₂ in WT increased significantly from (11.54 ± 0.44) mg/L to (15.23 ± 0.20) mg/L. In summary, N. daqingense is capable of absorbing or synthesizing vitamin B₁₂ in response to salt stress, suggesting that vitamin B₁₂ serves as a specific compatible solute effector for N. daqingense during salt stress.

The development of robust and efficient β-mannanases is key to advancing environmentally friendly industrial processes, such as guar gum fracturing fluid gel-breaking. Here, we report the identification and characterization of MG4, a novel thermotolerant and alkaliphilic β-mannanase mined from the Earth’s Microbiome database. The recombinant enzyme has a molecular weight of 63 kDa. MG4 displayed maximum activity at 65 °C and pH 9.0, and exhibited remarkable stability across a broad pH range (7.0–10.0). It retained over 80% of its activity after incubation at 50 °C for 1 h, and its activity was enhanced more than 40% by Mg²⁺ or Ca²⁺. Moreover, MG4 (20 mg/L) reduced the viscosity of guar gum fracturing fluid to <5 m·PaS within 30 min, outperforming ammonium persulfate (APS, 500 mg/L) which required 1 h, and produced 64.5% less insoluble residue. TEM imaging directly visualized the disruption of the guar gum polymer network by MG4, explaining its efficacy and suggesting reduced formation damage risk compared to chemical breakers. This work characterizes a highly promising biocatalyst whose thermostability, alkaliphily, efficient gel-breaking, low residue yield, and minimal formation damage potential position it as a superior, eco-friendly alternative for petroleum industry applications.