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Published on: February 11, 2010
Properties of bacteria that trigger hemocytopenia in the Atlantic blue crab, Callinectes sapidus
Nathaniel G Johnson1, Louis E Burnett, Karen G Burnett
1Grice Marine Laboratory, College of Charleston, 205 Fort Johnson Rd., Charleston, South Carolina 29412, USA. ngjohnson52@gmail.com
Insights
Bacterial infections in blue crabs cause respiratory problems by reducing circulating hemocytes. Gram-negative bacteria, particularly their lipopolysaccharide (LPS), are key drivers of this response, though other bacteria can also induce it.
Area of Science:
- Marine biology
- Crustacean immunology
- Pathogen-host interactions
Background:
- Bacterial infections in blue crabs (Callinectes sapidus) lead to decreased oxygen consumption.
- This impaired respiration is linked to bacterial and hemocyte aggregation obstructing gill vasculature.
- Hemocytopenia, a decrease in circulating hemocytes, is an indicator of this aggregation process.
Purpose of the Study:
- To identify bacterial properties that trigger hemocytopenia in blue crabs.
- To understand the role of lipopolysaccharide (LPS) in initiating hemocyte aggregation and respiratory impairment.
- To determine the range of bacterial species capable of inducing hemocytopenia and potentially affecting crab metabolism.
Main Methods:
- Injection of blue crabs with purified lipopolysaccharide (LPS) bound to beads.
- Injection of blue crabs with various gram-negative and gram-positive bacterial species.
- Assessment of circulating hemocyte counts following bacterial or bead injections.
Main Results:
- LPS-coated beads induced hemocytopenia comparable to Vibrio campbellii infection.
- Most gram-negative bacterial strains tested caused significant decreases in circulating hemocytes.
- A gram-positive bacterium (Bacillus coral), lacking LPS, also induced hemocytopenia, indicating LPS is not universally required.
Conclusions:
- Lipopolysaccharide (LPS) on gram-negative bacteria is a significant factor in inducing hemocytopenia in blue crabs.
- A diverse range of bacterial species, beyond just LPS-containing ones, can trigger hemocytopenia.
- These findings suggest that various bacterial infections can impair blue crab metabolism through hemocyte-mediated responses.
Abstract:
In the blue crab Callinectes sapidus, injection with the bacterial pathogen Vibrio campbellii causes a decrease in oxygen consumption. Histological and physiological evidence suggests that the physical obstruction of hemolymph flow through the gill vasculature, caused by aggregations of bacteria and hemocytes, underlies the decrease in aerobic function associated with bacterial infection. We sought to elucidate the bacterial properties sufficient to induce a decrease in circulating hemocytes (hemocytopenia) as an indicator for the initiation of hemocyte aggregation and subsequent impairment of respiration. Lipopolysaccharide (LPS), the primary component of the gram-negative bacterial cell wall, is known to interact with crustacean hemocytes. Purified LPS was covalently bound to the surfaces of polystyrene beads resembling bacteria in size. Injection of these "LPS beads" caused a decrease in circulating hemocytes comparable to that seen with V. campbellii injection, while beads alone failed to do so. These data suggest that in general, gram-negative bacteria could stimulate hemocytopenia. To test this hypothesis, crabs were injected with different bacteria--seven gram-negative and one gram-positive species--and their effects on circulating hemocytes were assessed. With one exception, all gram-negative strains caused decreases in circulating hemocytes, suggesting an important role for LPS in the induction of this response. However, LPS is not necessary to provoke the immune response given that Bacillus coral, a gram-positive species that lacks LPS, caused a decrease in circulating hemocytes. These results suggest that a wide range of bacteria could impair metabolism in C. sapidus.
