Isolation and Characterisation of the Agarolytic Bacterium Pseudoalteromonas Ruthenica

Abstract

Agar is a polysaccharide that primarily constitutes the cell wall of red algae. It is a good source of carbon and energy for many microbes. In the present study, an agarolytic bacterium, UQAD-3, was obtained from the waters of Al-Uqair, the Arabian Gulf, Al-Ahsaa, Saudi Arabia. UQAD-3 exhibited agarolytic activity when grown on agar as the sole source of carbon and energy. The strain was identified as Pseudoalteromonas ruthenica based on comparative analysis of the 16S rRNA, with 99.6% similarity. This finding was further confirmed by phylogenetic analyses based on 16S rRNA gene sequences, which highlighted that UQAD-3 was assembled within the Pseudoalteromonas clade and constituted a monophyletic subcluster with P. ruthenica, KMM 300^T. The strain was further characterised biochemically using the Biolog Gen III microtest system. UQAD-3 showed positive reactions to 16 (17%) of the 94 diverse traits assessed. Good growth was reported in 10% NaCl indicating its moderate halophilic nature. These observations indicate the agarolytic potential of the strain and opens new horizons for industrial applications in the future.

Keywords: Agarolytic bacteria; BIOLOG; Halophilic bacteria; Pseudoalteromonas.

Figure 1

Scanning electron micrographs showing the cell shape and arrangement of the strain UQAD-3. Magnification and scale bar are shown at the bottom of the image.

Figure 2

Agar degradation of the strain UQAD-3. A clear halo zone was formed around the colony upon addition of drops of iodine solution.

Figure 3

SDS-PAGE analysis of agarase. Lane M PageRuler™ Prestained Protein Ladder; lanes 1, 2 and 3 agarase.

Figure 4

Evolutionary relationships of the strain UQAD-3 and closely related reference species. The evolutionary history was inferred using the neighbour-joining method [32]. The optimal tree with branch length sum = 0.14946950 is shown. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Maximum Composite Likelihood method [34] and are in the units of the number of base substitutions per site. The analysis involved 17 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated. There were a total of 1352 positions in the final dataset. Evolutionary analyses were conducted in MEGA7 [22].