Michael Eisenbach

Michael Eisenbach is an Israeli biochemist who specializes in the navigation mechanisms of bacterial and sperm cells. He is a professor emeritus at the Weizmann Institute of Science, Department of Biomolecular Sciences, Rehovot, Israel. He discovered that sperm cells of mammals are actively guided to the egg. This opened the research field of mammalian sperm navigation.

Early life

Eisenbach was born in Tel Aviv, Israel on 10 April 1945. His parents, Menachem and Haya Eisenbach, were born in Poland and immigrated to Israel at the end of 1934. Most of their family members remained in Poland and were exterminated in the Holocaust.
Michael Eisenbach grew up in Tel Aviv and studied in an evening high school while working during the daytime as a messenger boy. He served his compulsory military term in the Israel Defense Forces in 1963–1966.

Education

Eisenbach attended Tel Aviv University. He received his B.Sc. in chemistry, M.Sc. and Ph.D. in biochemistry. For his M.Sc., he studied, under the supervision of Chanoch Carmeli, the photosynthetic electron transport chain in chloroplasts. For his Ph.D., he studied, under the supervision of Menachem Gutman, the respiratory electron transport chain in mitochondria.
He then moved to the Weizmann Institute of Science for postdoctoral study under the supervision of S. Roy Caplan, where he investigated the proton pump activity of bacteriorhodopsin in the purple membrane of archaea.
He did a second postdoctoral fellowship in Madison, Wisconsin, USA where he studied bacterial chemotaxis under the supervision of Julius Adler.

Academic career

In 1980, Eisenbach returned to the Weizmann Institute as a senior scientist and established his own research group as an independent investigator. Four years later he was promoted to associate professor with tenure, and in 1995 to professor. In 2015, he became a professor emeritus.
Eisenbach has held academic and leadership positions throughout his career, particularly within the Weizmann Institute of Science and in various national and international scientific organizations.

Research

Research on Sperm Navigation in Mammals

In the early 1990s, Eisenbach pioneered the study of mammalian sperm navigation, challenging the prevailing belief that such navigation was unnecessary due to the high number of spermatozoa in the female reproductive tract.
Eisenbach's group first showed that human spermatozoa accumulate in diluted follicular fluid, correlating with the fertilization potential of the corresponding egg.
They identified this accumulation as chemotaxis, defined criteria to distinguish it from other processes, and found that only capacitated spermatozoa are chemotactically responsive.
They discovered that the capacitated state in human spermatozoa is transient, lasting between 50 and 240 minutes in vitro. They found that within the sperm population, capacitated cells are continuously replaced, and that spermatozoa which are no longer capacitated are subsequently phagocytized by macrophages.
His team provided evidence that chemoattractants are secreted by the egg and surrounding cumulus cells post-ovulation.
Recognizing the short-range nature of chemotaxis, Eisenbach's research team discovered sperm thermotaxis as an additional, long-range navigation mechanism. They demonstrated that capacitated spermatozoa in humans, rabbits, and mice are capable of detecting and responding to temperature gradients comparable to, and even shallower than, those present in the oviduct during ovulation.
They identified opsins as thermosensors for sperm thermotaxis and elucidated two signaling pathways: one via rhodopsin and cyclic nucleotides, and another via melanopsin and phospholipase C.
Eisenbach linked hyperactivation to both sperm chemotaxis and thermotaxis. His research demonstrated that sperm cells adjust their turning frequency and hyperactivation events in response to chemical and thermal gradients, thereby elucidating the behavioral mechanisms underlying human sperm chemotaxis and thermotaxis.
Eisenbach proposed that sperm navigation not only guides sperm cells to the egg but also serves as a selection mechanism for capacitated spermatozoa, with potential implications for assisted reproduction.
In 2004, a startup company named Repromed was established to explore the use of thermotaxis to improve the success rate of artificial insemination. Although the company closed due to lack of funding before reaching the clinical trial stage, subsequent studies by other research groups later validated the concept.

Research on Bacterial Chemotaxis

Prior to and alongside his work on sperm navigation, Eisenbach conducted extensive research into the molecular mechanisms of chemotaxis in bacteria, particularly Escherichia coli and Salmonella. These organisms served as model systems for studying behavior at the molecular level. His group made significant contributions to understanding how bacteria regulate flagellar rotation in response to chemical gradients.
Key findings include:

The bacterial flagellar motor has a default rotation direction, which is reversed upon binding of the signal protein CheY to the switch complex.
CheY primarily binds to the N-terminus of the switch protein FliM. Phosphorylation of CheY enhances the interaction and promotes reversal of motor rotation.
CheY's activity is also modulated by acetylation, which plays a critical role in motor switching. In addition, Eisenbach's group elucidated the molecular mechanism underlying CheY acetylation.
The team also revealed the molecular events that occur at the switch complex following CheY–FliM binding.
Additionally, they identified fumarate as a switching factor, demonstrating its interaction with fumarate reductase and the switch protein FliG to induce directional changes in flagellar rotation.

Personal life

Eisenbach married Lea Eisenbach in 1967, divorced in 1985, and married Michal Schwartz in 1991. He has three sons.
Eisenbach started learning to play the clarinet at the age of 70. In 2021, he became a member of the Maskit Clarinet Choir and in 2023 a clarinet player in the Orchestra of the Weizmann Institute of Science.