The Discovery of Vitreoscilla Hemoglobin and Early Studies on Its Biochemical Functions, the Control of Its Expression, and Its Use in Practical Applications

In 1986, the surprising identification of a hemoglobin (VHb) in the bacterium Vitreoscilla greatly extended the range of taxa in which this oxygen binding protein functions. Elucidation of many of its biochemical properties and relation to overall cell physiology, as well as the sequence of the gene encoding it and aspects of control of its expression were determined in the following years. In addition, during the early years following its discovery, strategies were developed to use its expression in heterologous microbial hosts to enhance processes of practical usefulness. The VHb discovery also served as the foundation for what has become the fascinatingly rich field of bacterial hemoglobins. VHb’s position as the first known bacterial hemoglobin and its extensive use in biotechnological applications, which continue today, make a review of the early studies of its properties and uses an appropriate and interesting topic thirty-five years after its discovery.

Heterologous overexpression of bacterial hemoglobin VHb improves erythritol biosynthesis by yeast Yarrowia lipolytica

Background Yarrowia lipolytica is an unconventional yeast with a huge industrial potential. Despite many advantages for biotechnological applications, it possesses enormous demand for oxygen, which is a bottleneck in large scale production. In this study a codon optimized bacterial hemoglobin from Vitreoscilla stercoraria (VHb) was overexpressed in Y. lipolytica for efficient growth and erythritol synthesis from glycerol in low-oxygen conditions. Erythritol is a natural sweetener produced by Y. lipolytica under high osmotic pressure and at low pH, and this process requires high oxygen demand. Results Under these conditions the VHb overexpressing strain showed mostly yeast-type cells resulting in 83% higher erythritol titer in shake-flask experiments. During a bioreactor study the engineered strain showed higher erythritol productivity (QERY = 0.38 g/l h) and yield (YERY = 0.37 g/g) in comparison to the control strain (QERY = 0.30 g/l h, YERY = 0.29 g/g). Moreover, low stirring during the fermentation process resulted in modest foam formation. Conclusions This study showed that overexpression of VHb in Y. lipolytica allows for dynamic growth and efficient production of a value-added product from a low-value substrate.

Molecular Basis for the Evolution of Species-Specific Hemoglobin Capture by Staphylococcus aureus

ABSTRACT Metals are a limiting resource for pathogenic bacteria and must be scavenged from host proteins. Hemoglobin provides the most abundant source of iron in the human body and is required by several pathogens to cause invasive disease. However, the consequences of hemoglobin evolution for bacterial nutrient acquisition remain unclear. Here we show that the α- and β-globin genes exhibit strikingly parallel signatures of adaptive evolution across simian primates. Rapidly evolving sites in hemoglobin correspond to binding interfaces of IsdB, a bacterial hemoglobin receptor harbored by pathogenic Staphylococcus aureus. Using an evolution-guided experimental approach, we demonstrate that the divergence between primates and staphylococcal isolates governs hemoglobin recognition and bacterial growth. The reintroduction of putative adaptive mutations in α- or β-globin proteins was sufficient to impair S. aureus binding, providing a mechanism for the evolution of disease resistance. These findings suggest that bacterial hemoprotein capture has driven repeated evolutionary conflicts with hemoglobin during primate descent. IMPORTANCE During infection, bacteria must steal metals, including iron, from the host tissue. Therefore, pathogenic bacteria have evolved metal acquisition systems to overcome the elaborate processes mammals use to withhold metal from pathogens. Staphylococcus aureus uses IsdB, a hemoglobin receptor, to thieve iron-containing heme from hemoglobin within human blood. We find evidence that primate hemoglobin has undergone rapid evolution at protein surfaces contacted by IsdB. Additionally, variation in the hemoglobin sequences among primates, or variation in IsdB of related staphylococci, reduces bacterial hemoglobin capture. Together, these data suggest that S. aureus has evolved to recognize human hemoglobin in the face of rapid evolution at the IsdB binding interface, consistent with repeated evolutionary conflicts in the battle for iron during host-pathogen interactions.

Complete Genome Sequence of Vitreoscilla sp. Strain C1, Source of the First Bacterial Hemoglobin

Vitreoscilla sp. strain C1 is of historical importance as the source of the first prokaryotic hemoglobin identified.