Dr. Ying Huang has come quite a way from her early beginnings in marine biology – from a curious child in Xiamen, China to a Ph.D. graduate of the University of Hawai'i.
"I grew up right near the coast in southeastern China and was always fascinated by the different creatures in the ocean", recounts Dr. Huang. "It was because of this curiosity that I chose to study marine biology as my major in college."
After moving to Hawai'i to attend graduate school, Dr. Huang had to learn English through intensive study in order to take upper level classes at UH, serve as a teaching assistant in undergraduate biology classes, and read the primary literature in her field. She also had to learn cell and molecular biology and bacterial genetics and acquire advanced skills in molecular biology in order to successfully complete her dissertation research, a project that looked at the interaction between bacteria and invertebrates and the signal transduction between these two groups.
"For my dissertation research, I used the serpulid worm, Hydroides elegans, as a model organism to study the nature of the bacterial cues that bring about settlement and metamorphosis in invertebrate larvae," explains Dr. Huang.
Communities of benthic marine animals are established and maintained by recruitment of larvae of their member species. Where the larvae choose to settle among a diverse benthic community involves chemical cues that guide them towards conspecific individuals or other associated species. With the appropriate cues, the larvae will contact the substrate and begin the process of metamorphosing into the adult form. Many of the chemical cues come from bacteria that make up marine biofilms. The invertebrate larvae are able to differentiate between characteristics of a biofilm such as age, bacterial density, biochemical signals, and the overall community composition.
Exactly what the molecular cues are, and how they are interpreted by the larvae, is an important question for both ecological and economic reasons. In the case of the marine worm Hydroides, the calcareous tube the adult secretes after metamorphosis becomes firmly cemented to the substrate and can impact the local community structure through modification of the habitats where they settle. These types of biofouling organisms can also have a large economic impact due to the costs associated with removal of the worms from ship hulls and other submerged structures where they may settle.
"It is hoped that understanding the cues that induce larvae to settle can provide information that can be used to prevent their unwanted settlement on marine structures," says Dr. Huang.
As part of her research, Dr. Huang looked at the relationship between bacteria in the biofilm and the induction of settlement in Hydroides to determine the nature of the bacterial cues that bring about settlement and metamorphosis in marine invertebrate larvae.
"Competent larvae of Hydroides are induced to settle and rapidly metamorphose by the presence of a well developed biofilm, such as biofilm of the bacterium Pseudoalteromonas luteoviolacea (HI1)," explains Dr. Huang. "Although the relationship between bacteria and induction of settlement in Hydroides has been the subject of many investigations, the particular molecular cues and molecular mechanisms by which P. luteoviolacea (HI1) induces metamorphosis of Hydroides remain unknown."
Dr. Huang applied a molecular approach to identify the genes from P. luteoviolacea (HI1) whose products are necessary to induce settlement and metamorphosis in Hydroides. To do this, she employed a strongly inductive bacterial strain (previously isolated and identified in the Hadfield lab) to create transposon mutants, screen them for loss of inductive capacity, and then extensively analyze the parts of the bacterial genome that were altered.
Using these gene-knockout mutants or gene-deletion mutants, Dr. Huang has been successful in identifying the first putative bacterial operon required for the induction of settlement and metamorphosis of Hydroides larvae, a process that is critical to the establishment and maintenance of benthic marine communities.
An operon is a stretch of DNA containing several genes whose products are co-involved in a shared pathway, and whose expression is under the control of a single regulatory sequence. The operon Dr. Huang identified in P. luteoviolacea (HI1) consists of seven genes, four of which whose products are necessary for the induction process.
"What was even more surprising is that this operon may be unique to the inductive strain of P. luteoviolacea," adds Dr. Huang. "When I compared the DNA sequences of my inductive strain, P. luteoviolacea (HI1), to that of a non-inductive strain, P. luteoviolacea ATCC3349, I was not able to find the operon gene sequences in the non-inductive strain, which is 99.9% identical in 16s rDNA gene sequences with P. luteoviolacea (HI1)."
Dr. Huang also analyzed the organization and potential functions of these genes by bioinformatics and by examining the expression of these genes. Dr. Huang hopes that by establishing genetic markers that can be used to evaluate the inductive capacity of a wide spectrum of bacteria we will be able to better understand the role of biofilms in larval settlement and metamorphosis for many species that in turn may aid antifouling strategies.
Hydroides larvae are present on wild type P. luteoviolacea (HI1) biofilm. They slow down and crawl on the bottom as they sense the settlement cues and try to settle. (Video by Ying Huang).
Hydroides larvae on biofilms of a transposon mutant of P. luteoviolaeca (HI1). They swim fast and do not crawl indicating the settlement cues on the surface are absent because transposons have disrupted the genes involved in producing settlement cues in the mutant Plm9. (Video by Ying Huang).