Cobalamin cbiP mutant shows decreased tolerance to low temperature and copper stress in Listeria monocytogenes

Transcriptome Analysis Reveals the Important Role of Vitamin B12 in the Response of Natronorubrum daqingense to Salt Stress

Natronorubrum daqingense JX313T 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 JX313T, 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.

Vitamin B12 conveys a protective advantage to phycosphere-associated bacteria at high temperatures

Many marine microbes require vitamin B12 (cobalamin) but are unable to synthesize it, necessitating reliance on other B12-producing microbes. Thus, phytoplankton and bacterioplankton community dynamics can partially depend on the production and release of a limiting resource by members of the same community. We tested the impact of temperature and B12 availability on the growth of two bacterial taxa commonly associated with phytoplankton: Ruegeria pomeroyi, which produces B12 and fulfills the B12 requirements of some phytoplankton, and Alteromonas macleodii, which does not produce B12 but also does not strictly require it for growth. For B12-producing R. pomeroyi, we further tested how temperature influences B12 production and release. Access to B12 significantly increased growth rates of both species at the highest temperatures tested (38 °C for R. pomeroyi, 40 °C for A. macleodii) and A. macleodii biomass was significantly reduced when grown at high temperatures without B12, indicating that B12 is protective at high temperatures. Moreover, R. pomeroyi produced more B12 at warmer temperatures but did not release detectable amounts of B12 at any temperature tested. Results imply that increasing temperatures and more frequent marine heatwaves with climate change will influence microbial B12 dynamics and could interrupt symbiotic resource sharing.

Genome mining reveals abiotic stress resistance genes in plant genomes acquired from microbes via HGT

Colonization by beneficial microbes can enhance plant tolerance to abiotic stresses. However, there are still many unknown fields regarding the beneficial plant-microbe interactions. In this study, we have assessed the amount or impact of horizontal gene transfer (HGT)-derived genes in plants that have potentials to confer abiotic stress resistance. We have identified a total of 235 gene entries in fourteen high-quality plant genomes belonging to phyla Chlorophyta and Streptophyta that confer resistance against a wide range of abiotic pressures acquired from microbes through independent HGTs. These genes encode proteins contributed to toxic metal resistance (e.g., ChrA, CopA, CorA), osmotic and drought stress resistance (e.g., Na⁺/proline symporter, potassium/proton antiporter), acid resistance (e.g., PcxA, ArcA, YhdG), heat and cold stress resistance (e.g., DnaJ, Hsp20, CspA), oxidative stress resistance (e.g., GST, PoxA, glutaredoxin), DNA damage resistance (e.g., Rad25, Rad51, UvrD), and organic pollutant resistance (e.g., CytP450, laccase, CbbY). Phylogenetic analyses have supported the HGT inferences as the plant lineages are all clustering closely with distant microbial lineages. Deep-learning-based protein structure prediction and analyses, in combination with expression assessment based on codon adaption index (CAI) further corroborated the functionality and expressivity of the HGT genes in plant genomes. A case-study applying fold comparison and molecular dynamics (MD) of the HGT-driven CytP450 gave a more detailed illustration on the resemblance and evolutionary linkage between the plant recipient and microbial donor sequences. Together, the microbe-originated HGT genes identified in plant genomes and their participation in abiotic pressures resistance indicate a more profound impact of HGT on the adaptive evolution of plants.