Assoc. Prof. Marco Polin
University of Warwick, UK

Phototaxis of microalgae: lessons from Chlamydomonas an Micromonas

　Microbial motility is often characterised by complex responses to environmental physico-chemical stimuli. Here I will focus on phototaxis, the ability of many microorganisms to move towards or away from light. I will discuss two important examples within the realm of microalgae, those of Chlamydomonas reinhardtii, an important biological model system, and of Micromonas, a pico-eukaryote globally dominant in marine ecosystems.
　In the former case, we will leverage Chlamydomonas’ phototactic ability to precisely control the timing and position of localised cell photo-accumulation, leading to the controlled development of isolated bioconvective plumes. This type of photo-bio-convection allows a precise, fast and reconfigurable control of the spatio-temporal dynamics of the instability and the ensuing global recirculation, which can be activated and stopped in real time. We will then discuss briefly our current attempts at understanding the role that cell photosynthesis is playing in its phototactic response.
　In the latter, we will report on the first quantitative characterisation Micromonas’ phototaxis. Starting at the population scale, we show that this organism actively responds to a wide range of light wavelengths and intensities. These population responses follow a simple drift-diffusion framework displaying a all-or-none-type response to light. Single-cell tracking experiments allow us to first detail thoroughly the way Micromonas explore its environment and then highlight the microscopic changes in motility that allow this microalga to drift towards light despite the absence of a dedicated light-sensitive organelle.

Prof. Sanjay P. Sane
Tata Institute of Fundamental Research, India

Flying in sync: how flight reflexes are coordinated in insects

　A remarkable aspect of insect flight is that their wing movements are both extremely fast and very precisely coordinated. The wingbeat frequencies of insects ranges from 10-1000 Hz. In most insects, flight onset is characterized by several stereotypic reflexes, including the forward positioning of their antennae to obtain vestibular and olfactory inputs, the head stabilization reflex to reduce motion blur, the abdominal flexion reflex which is used for aerial balance, leg extension to push the ground, and wing flapping for flight. At high wingbeat frequencies, the mutual coordination of these diverse reflexes is absolutely crucial, because the slightest errors can cause loss of control. How are these reflexes coordinated in insects? We have recently been exploring this question in depth in the hawkmoth Daphnis nerii. Our initial investigation involved a detailed characterization of the antennal positioning response, for which we developed diverse neuroanatomical and neurophysiological tools. More recently, we have used these tools in the investigation of other reflexes, and also explored how coordination occurs in the context of airflow-mediated flight initiation. In Diptera, we additionally explored how wings and halteres (the gyro-sensory hindwings) are coordinated. In my seminar, I will describe our diverse findings on this topic.

Prof. Eleonora Secchi
ETH Zurich, Switzerland

"What shapes bacterial biofilms? A Physics perspective"

　Biofilms are aggregates of microorganisms in which cells are embedded in a self-secreted matrix of extracellular polymeric substances (EPS) and are adherent to each other and/or to a surface. The composition of the matrix can vary greatly depending on the microorganisms present and the environmental conditions. However, its functions are universal: the matrix forms the scaffold of the biofilm structure, is responsible for adhesion to surfaces and internal cohesion, keeps the cells in close proximity, thus favoring interactions, and protects the microbial community from chemical and mechanical insults. Despite its importance, the matrix – "the dark matter of biofilms"– remains the least understood component of biofilms.
　Our work aims to understand how the material properties of the biofilm matrix determine biofilm morphology and mechanical properties. We present examples of biofilms grown in different environmental conditions, ranging from the air-solid interface of agar plates [3,4] to surfaces exposed to fluid flow and porous media, and by different bacterial species. In each case, we show that the interplay between biology-driven forces, i.e., growth, and physics-driven ones, i.e., surface adhesion, osmotic pressure, and shear stress, controls biofilm morphology, rheology, and, ultimately, affects the physiological protective function of biofilms. By shedding light on this interplay, we can control biofilm development, showing the prominent role physics can play in developing novel antimicrobial and antifouling strategies.

Dr. Koraon Wongkamhaeng
Kasetsart University, Thailand

Mating behaviour of Cerapus sp. (Amphipoda: Ischyroceridae), a tube builder amphipod in Amphawa Estuary, the inner Gulf of Thailand

　The tube-builder amphipods genus Cerapus have been reported as circumtropical worldwide. During the survey on amphipod diversity in Amphawa Estuary, several Cerapus sp. were found attached to the settlement pad. In the laboratory, the large males rove about the other tube investigating other individuals. During the observation, one male started by searching for the female in her tube using their second antenna. After that, the mating was made by the male entering in and out into the female tube several times and putting the posterior body halfway into the female tube. The female carried the fertilized eggs in their brood pouch until hatched, and the juvenile created their tube attached to the mother tube. Further study on the factors of mating stimulation and the behaviour inside the tube is needed.