Host range expansion of Acinetobacter phage vB_Ab4_Hep4 driven by a spontaneous tail tubular mutation

Bacteriophages (phages) represent promising alternative treatments against multidrug-resistant Acinetobacter baumannii (MDRAB) infections. The application of phages as antibacterial agents is limited by their generally narrow host ranges, so changing or expanding the host ranges of phages is beneficial for phage therapy. Multiple studies have identified that phage tail fiber protein mediates the recognition and binding to the host as receptor binding protein in phage infection. However, the tail tubular-dependent host specificity of phages has not been studied well. In this study, we isolated and characterized a novel lytic phage, vB_Ab4_Hep4, specifically infecting MDRAB strains. Meanwhile, we identified a spontaneous mutant of the phage, vB_Ab4_Hep4-M, which revealed an expanded host range compared to the wild-type phage. A single mutation of G to C was detected in the gene encoding the phage tail tubular protein B and thus resulted in an aspartate to histidine change. We further demonstrated that the host range expansion of the phage mutant is driven by the spontaneous mutation of guanine to cytosine using expressed tail tubular protein B. Moreover, we established that the bacterial capsule is the receptor for phage Abp4 and Abp4-M by identifying mutant genes in phage-resistant strains. In conclusion, our study provided a detailed description of phage vB_Ab4_Hep4 and revealed the tail tubular-dependent host specificity in A. baumannii phages, which may provide new insights into extending the host ranges of phages by gene-modifying tail tubular proteins

Changes in the Anatomic and Microscopic Structure and the Expression of HIF-1α and VEGF of the Yak Heart with Aging and Hypoxia - Fig 3

<p>A: The diameter of collagen fiber. B: The optical density of collagen fiber.</p

Comparison of histological characteristics and expression of CD3 and CD79a among the hemal nodes, lymph nodes and spleens of yaks (Bos grunniens)

This experiment compared the histological characteristics and distribution of CD3 and CD79a among yak lymph nodes, hemal nodes and spleen. The three organs from ten clinically healthy newborn and adult yaks were studied using histology and immunohistochemistry. The yak hemal nodes, which consisted of blood sinuses, lymphoid follicles, diffuse lymphoid tissue and lymphoid cords, appeared to share the histological characteristics of the spleen and lymph nodes: the lymphoid follicles of the hemal nodes were much like those of the lymph nodes, which were not surrounded by the central artery and periarteriolar lymphoid sheath. The lymphoid cords of the hemal node, which contained many erythrocytes, were much like the splenic cords. The sinuses of the hemal nodes had a similar structure to the lymph sinuses of the lymph nodes but were engorged with erythrocytes rather than lymph as in the lymph nodes. Interestingly, the splenic sinuses of yak were of two different types: the sinuses with obvious endothelial cells or those consisting of reticular cells. The CD3+ cells were mainly located in the paracortex area and medulla of the lymph nodes, the diffuse lymphoid tissues of the hemal nodes, and the periarteriolar lymphoid sheaths and red pulp of the spleen. Most CD79a+ cells were mainly detected in the lymphoid follicles of all examined lymphoid organs. The results suggested that although the three organs had specific characteristics, in some respects, they had similar organizational structural characteristics and immune functions. These may be useful to better understand the relationship between the morphology and function of these organs and provide useful references for normal yak lymphoid organs

The weight of heart and yak, and the length of heart perimeter.

<p>The weight of heart and yak, and the length of heart perimeter.</p

HIF-1α and VEGF protein expression in the yak heart were measured by ELISA.

<p>A: HIF-1α expression. B: VEGF expression.</p

Thickness of vascular intima and tunicae media vasorum inrami anterior descendens, left and right circumflex of coronary artery.

<p>Unit: μm.</p

Immunogold labeling of HIF-1α and VEGF protein in the yak heart.

<p>A: Electron microscope images showing HIF-1α immunopositive silver grains in endothelial cells (arrowheads). B: HIF-1α immunopositive silver grains in cardiac muscle cells. C: No HIF-1α immunopositive silver grains in smooth muscle cells. D: Electron microscope images showing VEGF immunopositive silver grains in smooth muscle cells. E: VEGF immunopositive silver grains in endothelial cells (arrowheads). F: High magnification of VEGF immunopositive silver grains in endothelial cells (arrowheads). G: Some fine filaments were found in smooth muscle cells (boxed area). H: Smooth muscle cell has a higher electron density than endothelial cells. I, J: No gold particles were found in control sections. SMC: smooth muscle cell, EC: endothelial cell, EF: elastic fiber, SEF: secondary elastic fiber.</p

Thickness of the ventricular wall of heart in yak.

<p>Unit: cm.</p

The microscope structures of coronary artery.

<p>A: A monolayer of endothelial cell adhered to internal elastic membrane in 1-day old yak (arrowheads) (Massion trichrome). B: An integral structure of the left circumflex of coronary artery in 1-day old yak (Massion trichrome). C: Internal elastic membrane was disrupted in heart of 6-month old yak (arrowheads) (VVG). D: The internal elastic membrane was divided into two layers in 1-year old yak (arrowheads) (VVG). E: Those internal elastic membrane and smooth muscle cells together form Muscle elastic zone in 2-year old yak (arrowheads) (VVG). F: Secondary internal elastic membrane ruptured, or even fall off, and smooth muscle membrane exposed in old yak (arrowheads) (VVG).</p

The ultra-structural changes of mitochondria in the yak heart with aging.

<p>A: Mitochondria aggregated around the nucleus in 1-day-old yak (arrowheads); B: Mitochondria ridge was uniform and well distributed (arrowheads) in 6-month-old yak. C: Giant mitochondria and the irregular ridge in 5-year-old yak (arrowheads). D, E, F: Collagen fibers in the 1-day-old, 6-month-old, and 2-year-old yak heart.</p