Phylogenetic characterization of a novel radiation-resistant bacterium from irradiated pork: description of Hymenobacter actinosclerus sp. nov

Researchers identified a novel radiation-resistant bacterium isolated from irradiated pork and characterized it using phylogenetic analysis. The red-pigmented, Gram-negative rod-shaped organism was subjected to 16S rRNA gene sequencing and comparative biochemical analysis. Results showed the bacterium belongs to the Cytophaga-Flavobacterium-Bacteroides line of descent, not to the Deinococcus genus where most radiation-resistant bacteria reside. The organism exhibited radiation resistance comparable to Deinococcus species, with D₁₀ values of 3.45 kGy in buffer and 5.05 kGy on pork mince. Its cell wall contained meso-diaminopimelic acid typical of Gram-negative bacteria, and its fatty acid and menaquinone compositions resembled Cytophaga-Flavobacterium members rather than deinococci. Phylogenetic analysis revealed closest associations with Hymenobacter roseosalivarius and provisional Taxeobacter species. Based on these findings, the authors propose classification of this bacterium as a new species within the genus Hymenobacter, named Hymenobacter actinosclerus. The discovery demonstrates that radiation resistance exists across diverse bacterial lineages and highlights implications for food irradiation treatments.

Key findings

• A novel radiation-resistant bacterium was isolated from irradiated pork and identified as a new species, Hymenobacter actinosclerus, belonging to the Cytophaga-Flavobacterium-Bacteroides phylogenetic line.
• The organism demonstrated high radiation resistance (D₁₀ = 3.45-5.05 kGy) comparable to Deinococcus species but distinct biochemical and genetic characteristics.
• 16S rRNA gene sequencing showed only ~77% similarity to known radiation-resistant bacteria, establishing it as phylogenetically distant from deinococci and other characterized radiotolerant organisms.
• The bacterium's cell wall chemistry, fatty acid composition, and menaquinone profile (MK-7) are consistent with Cytophaga-Flavobacterium members, contrasting markedly with Deinococcus properties.
• The discovery expands understanding of radiation resistance phylogenetic diversity and raises concerns about effectiveness of low-dose food irradiation against this novel resistant bacterium.