Summary auto-generated
Researchers isolated four strains of aerobic, spore-forming bacteria from the inner tissues of healthy cotton plants (Gossypium sp.) grown in Tajikistan. Using morphological, physiological, and molecular analyses including RAPD patterns, 16S–23S rRNA spacer analysis, and 16S rRNA gene sequencing, the researchers characterized these bacteria. The four strains showed nearly identical 16S rRNA sequences, differing at only two sites, and demonstrated unique characteristics distinguishing them from known plant-associated Bacillus species such as B. licheniformis, B. megaterium, B. pumilus, and B. subtilis. Phylogenetic analysis placed the new isolates closest to Bacillus sporothermodurans (94.8% 16S rRNA sequence similarity). The bacteria are Gram-positive rods occurring in short or filamentous chains, with ellipsoidal spores and optimal growth at 28°C. They lack starch and casein hydrolysis, produce acid from multiple sugars, and can survive in 10% NaCl and ampicillin. Based on molecular and phenotypic evidence, the authors propose classification as a novel species, Bacillus endophyticus, with strain 2DTT designated as the type strain.
Key findings
- Four Bacillus strains isolated from cotton plant tissues represent a novel species, Bacillus endophyticus, distinguished from common plant-associated bacilli by RAPD analysis and rRNA sequencing
- The four strains exhibited nearly identical 16S rRNA sequences (differing by only 2 bases) supporting classification as a single species
- Strain 2DTT showed 94.8% 16S rRNA sequence similarity to B. sporothermodurans, establishing it as sufficiently distinct to warrant new species status
- The organisms display characteristics consistent with endophytic habitat preference, including microaerophilic metabolism, lack of extracellular protease and amylase, and optimal growth temperature of 28°C
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Abstract
Four strains of aerobic, endospore-forming bacteria were isolated from the inner tissues of healthy cotton plants (Gossypium sp., Dushanbe, Tajikistan). The organisms had identical randomly amplified polymorphic DNA patterns that distinguished them from other bacilli that are commonly isolated from plant tissues, e.g. Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus pumilus and Bacillus subtilis. PCR amplification of 16S--23S rRNA spacer regions suggested that the four strains could be assigned to two highly related taxa, which correlated with differences in cell morphology. However, the cloned spacer region provided a simple and specific hybridization probe for all four strains. The virtually complete 16S rDNA sequences were prepared for representatives of the two groups (strains 2DT(T) and 12DX) and differed by only two bases, thus supporting classification of the four strains in a single taxon at the species level. Phylogenetic analyses indicated that strain 2DT(T) belonged to the genus Bacillus and was most closely related to Bacillus sporothermodurans DSM 10599(T) with a sequence similarity of 94.8%. It is concluded that the four strains belong to a novel species of Bacillus for which the name Bacillus endophyticus sp. nov. is proposed. The type strain is 2DT(T) (=UCM B-5715(T)=CIP 106778(T)).