Zinc is a micronutrient important in several biological processes including growth and development. We have limited knowledge on the impact of maternal zinc deficiency on zinc and zinc regulatory mechanisms in the developing embryo due to a lack of in vivo experimental models that allow us to directly study the effects of maternal zinc on embryonic development following implantation. To overcome this barrier, we have proposed to use zebrafish as a model organism to study the impact of zinc during development. The goal of the current study was to profile the mRNA expression of all the known zinc transporter genes in the zebrafish across embryonic and larval development and to quantify the embryonic zinc concentrations at these corresponding developmental time points. The SLC30A zinc transporter family (ZnT) and SCL39A family, Zir-,Irt-like protein (ZIP) zinc transporter proteins were profiled in zebrafish embryos at 0, 2, 6, 12, 24, 48 and 120 hours post fertilization to capture expression patterns from a single cell through full development. We observed consistent embryonic zinc levels, but differential expression of several zinc transporters across development. These results suggest that zebrafish is an effective model organism to study the effects of zinc deficiency and further investigation is underway to identify possible molecular pathways that are dysregulated with maternal zinc deficiency.

SummaryCell‐based biosensors have been proposed for use as function‐based detectors of toxic agents. We report the use of Betta splendens chromatophore cells, specifically erythrophore cells, for detection of food‐associated pathogenic bacteria. Evaluation of erythrophore cell response, using Bacillus spp., has revealed that this response can distinguish pathogenic Bacillus cereus from a non‐pathogenic B. cereus ΔplcR deletion mutant and a non‐pathogenic Bacillus subtilis. Erythrophore cells were exposed to Salmonella enteritidis, Clostridium perfringens and Clostridium botulinum. Each bacterial pathogen elicited a response from erythrophore cells that was distinguished from the corresponding bacterial growth medium, and this observed response was unique for each bacterial pathogen. These findings suggest that erythrophore cell response has potential for use as a biosensor in the detection and toxicity assessment for food‐associated pathogenic bacteria.

Toxicant sensing technology has evolved to include biological sensors, such as cell-based biosensors, which rely on viable cells to convey a measurable physiological signal. Chromatophores are a class of pigment cells that have been investigated as cell-based biosensors. We report the characterization of Oncorhynchus tshawytscha melanophores and describe the melanophore pigment response to neurotransmitters in terms of pigment area occupied. Compared with the previously described model, Betta splendens erythrophores, O. tshawytscha melanophores responded similarly, indicating that pigment responses are biologically conserved between these two species. Additionally, melanophores responded to mercuric chloride and sodium arsenite, similar to B. splendens erythrophores, suggesting that melanophores can be used as detectors for environmental toxicants. This report highlights the potential of O. tshawytscha melanophores to be used as cell-based biosensors to address environmental toxicity, and warrants a continued investigation to strengthen this technology and its applications.

Chromatophore cells have been investigated as potential biodetectors for function-based detection of chemically and biologically toxic substances. Oncorhynchus tshawytscha (chinook salmon) melanophores, a chromatophore cell type containing brown pigment, rapidly detect the salmonid pathogens Aeromonas salmonicida, Yersinia ruckeri, and Flavobacterium psychrophilum and the human pathogen Bacillus cereus.Chromatophores are a class of pigment cells present in amphibians, cephalopods, and fish that have been used as biodetectors to report toxicity (1,2,7,8,9,14). Upon exposure to explicit toxic stimuli, chromatophores redistribute their intracellular pigment organelles in one of two directions. Aggregation describes pigment organelle movement to the perinuclear region, and conversely, dispersion indicates the relocation of pigment organelles to the outer periphery of the intracellular space. These pigment responses are monitored optically and can vary by the degree of aggregation or dispersion as well as the rate of pigment movement for different toxic substances.We previously described the Oncorhynchus tshawytscha (chinook salmon) melanophore response and have shown that pigment dynamics of melanophores and Betta splendens (Siamese fighting fish) erythrophores are conserved in their responses to the environmental toxicants mercury and arsenic (2). Melanophores and erythrophores each belong to the chromatophore class and differ by containing brown and red pigment organelles, respectively. While erythrophores have been explored for their responsiveness to bacterial pathogens, such as Bacillus cereus and Clostridium botulinum (1,7,14), the potential for melanophores to be utilized in this capacity has not yet been investigated. This study addresses melanophores in their ability to respond to the salmonid bacterial pathogens Yersinia ruckeri, Aeromonas salmonicida, Flavobacterium psychrophilum, and Carnobacterium piscicola and the human bacterial pathogens Bacillus cereus and Clostridium botulinum.We hypothesized that melanophores would respond to B. cereus and C. botulinum through pigment aggregation, similar to observations previously reported for B. splendens erythrophores (7). The salmonid bacterial pathogens described in this study have not been analyzed with respect to B. splendens erythrophores or any other chromatophore detection system. However, a disease characteristic for both enteric red mouth disease, caused by Y. ruckeri, and bacterial cold water disease, caused by F. psychrophilum, is melanosis, or darkening of the tissues (4, 17). Therefore, we hypothesized that Y. ruckeri and F. psychrophilum would induce pigment dispersion in isolated melanophores. Ill fish, in general, have been observed to appear either pale or darker in color, and due to this dichotomy, no preconceived notions were made concerning the O. tshawytscha melanophore responses to A. salmonicida and C. piscicola.The Oregon Department of Fish and Wildlife (ODFW) provided hatchery-raised O. tshawytscha for all melanophore preparations and a...