THE AARON KAPLAN LAB
Lab members
Aaron Kaplan, full professor
Principal investigator
​
​
​
​
​
Judy Lieman-Hurwitz, Ph.D.
Lab manager
After many years of studying changes in gene expression of cyanobacterial genes under growth conditions of high and low CO2 through the use of various mutants plus a study of the expression of one of these genes in higher plants, I have more recently turned my attention to the study of promoters themselves to further understand the role of the DNA sequences recognized by RNA polymerase and various transcription factors. This study was initiated in E. coli because of its ability to grow faster than cyanobacterial cultures and because of the larger amount of information about E. coli promoters readily available in the literature.
Since the important -35 and -10 regions of the bacterial promoter were already identified in E. coli years ago, my study has focused on the sequences of the lesser known spacer region and the areas surrounding the -35 and -10 sequences which play a role in the "fine-tuning" of gene expression. In order to further understand how the bacteria "read" the fine-tuning sequences, I have isolated many mutants in these regions showing varying levels of gene expression using the Venus yellow fluorescent protein reporter gene. In addition, I have created my own promoter sequences and site-specific mutations which show variations in gene expression as determined by both fluorescence measurements and qPCR. Experiments are in progress to verify the gene expression results using a different reporter gene. In parallel, work is progressing on the second part of the project which will examine how the bacteria read these sequences in order to differentiate between stronger and weaker promoters.
Omer Murik, Ph.D.
Postdoc
I study the various factors allowing photosynthetic microbes to survive one of the harshest ecosystems on Earth – the desert. Our two cases of study are a cyanobacterium (Leptolyngbya ohadii) and a eukaryotic green algae (Chlorella ohadii), inhabiting biological soil crusts near Nitzana, Israel. These organisms can tolerate extreme light intensities, extreme high day temperatures and frequent desiccation/hydration cycles. I focus on the genomics aspect related to the question of “how do they do it?”. We sequenced, assembled and annotated the genomes and transcriptomes of the 2 organisms. For the cyanobacterium I used the comparative genomic approach to identify genes found only in desiccation tolerant cyanobacteria but not in sensitive species (for details, see: Murik, Omer, et al. (2017) "What distinguishes cyanobacteria able to revive after desiccation from those that cannot: the genome aspect." Environmental Microbiology 19: 535-550). For the green algae, we are combining the transciptome analyses of cells exposed to stress with comparative genomics of closely related algae in order to find genes related to its unusual physiology under stress. These analyses may contribute to the identification of novel stress tolerance pathways, making them potential targets for basic research on the evolution processes of adaptation of microbes to their environment as well as targets for genetically improved crop plants.
Haim Treves, Ph.D.
Postdoc
In the last few years I've been exploring the properties of a unique green desert alga, Chlorella ohadii, which does not conform to some of the basic dogmas in microbial ecology and photosynthesis:
-
Acquiring ability to acclimate to extreme environments is usually accompanied by reduced performance under optimal conditions. We showed that C. ohadii does not obey this rule; when grown under optimal laboratory conditions it exhibits the fastest growth rates ever reported for an alga.
-
Many years of intensive research provided us with basic understanding of the functioning of algal growth and the photosynthetic machinery. However, the unparalleled fast growth, extremely high photosynthetic rates and resistance to photodamage, suggest that we may still lack essential knowledge. We showed that C. ohadii is completely resistant to photoinhibition, does not suffer from photodamage and its productivity is unaffected by irradiances as high as twice full sun light.
I think that C. ohadii is an example for two main points we should consider. First, as we expected when we focused on the BSC's, unique capabilities can be found in microorganisms facing extremely harsh conditions, and there's no better example for that than this "super-bug". And second, one should be familiar with the relevant literature but always bear in mind that not all organisms have read and comply with it.
​
Presently a post doc with Mark Stitt at the Max Planck , Golm, Germany
Nadav Oren
Ph.D. student
Sands in hot and cold deserts are often covered by biological soil crusts (BSC). The BSC stabilizes the sand, and its destruction by anthropogenic and global change is a major cause of desertification. The BSCs are formed by the adhesion of soil particles to extracellular polysaccharides excreted mainly by filamentous cyanobacteria, the pioneers and main primary producers in the BSC. The organisms inhabiting the BSCs are exposed to one of the most extreme and fluctuating environmental regimes in nature including frequent hydration/ dehydration cycles, extreme irradiance, temperature amplitudes ranging from subfreezing during winter nights to over 60°C in midsummer days and vast osmotic potential changes. To study the abilities of filamentous cyanobacteria to cope with this environment, we isolated an axenic culture of Leptolyngbya sp. named Leptolyngbya ohadii from BSC samples withdrawn from the Nizzana field station of the Hebrew University. To mimic the environmental conditions prevailing in the crust, we constructed a fully automated environmental chamber capable of accurately simulating the dynamic abiotic conditions in the field. Global RNA profiling, RT qPCR, mutants and physiological methodologies are used to study the mechanisms whereby these filamentous cyanobacteria senses and responds to environmental signals, enabling it to survive frequent hydration/dehydration cycles. We use both isolated Leptolyngbya ohadii and whole desert biological soil crusts as models systems.
Gad Weiss
Ph.D. student
I am interested in the interactions between cyanobacteria and other organisms in their surroundings. Such interactions determine, to a large extent, which organisms will live long and prosper in the water body, and if cyanobacteria blooms will form.
In many fresh water bodies around the world, formation of large toxic cyanobacteria populations, a phenomenon known as blooms, especially of Microcystis aeruginosa has increased in the last 15 years. During these blooms, a variety of harmful secondary metabolites are produced and released in to the water, up to the level that poses a danger to people, livestock, fish and even crops.
During my research, I recently found that the bacteria Aeromonas veronii, isolated from scum samples of a Microcystis sp bloom in Lake Kinneret, can inhibit the growth of Microcystis. I have isolated an active material from the Aeromonas veronii culture that affects Microcystis at ppb levels. A mutant in which the biosynthetic pathway of this material is impaired was created to further study the dialog between Microcystis and Aeromonas veronii. This dialog is mediated by infochemicals, which are a form of language the organisms use in the water body. The effect of this dialog on different organisms may help answer the question – what/who determines who is there?
Isaac Kedem
Ph.D. student
Extreme environments often give rise to organisms with extreme capabilities. When studying organisms from desert Biological Sand Crusts (BSCs) – among the harshest habitats on earth – we are accustomed to find organisms with good tolerance to high light intensities. Chlorella ohadii, a recently discovered BSC-inhabiting green alga, stands out even in this context. C. ohadii’s tolerance to high light extends to intensities higher than can be naturally experienced on Earth (a truly unprecedented capability), while maintaining an exceptionally high growth rate. My interest is largely in the energetics of these cells, and in deciphering the mechanisms used to disperse excess photochemical energy under high light conditions; I also hope to better elucidate the regulation of different energetic pathways under changing conditions. In support of this research, I am working on optimizing a transformation protocol which will allow genetic manipulation in C. ohadii. Besides opening up many options in basic research of this organism, such a protocol could enable the use of C. ohadii for biotechnological pursuits. With its unique combination of fast growth and light tolerance, this alga could well become a powerhouse in biotechnological algal systems.
Shany Gefen-Treves
Ph.D. student
My favorite local landscapes are the Vermetid-built abrasion platforms of the Israeli rocky shore. Vermetid-reefs in the Mediterranean Sea and the rocky shore are hot-spots of biodiversity with economic and cultural importance for Israel national resources, setting them as the subtropical equivalent of coral reefs. The reefs depend for their existence on the actively-built rims constructed by several reef builders; among them are two species of intertidal Vermetid gastropods and the red Crustose Coralline alga (CCA), Neogoniolithon brassica-florida, yet their biogenic role is threatened by a rapidly changing environment. We managed, for the first time, to grow N. brassica-florida on glass slides dissecting it from the reef consortium and allowing characterization of its photosynthetic performance and response to various illumination levels. Surprisingly, N. brassica-florida was found to be far more sensitive to illumination than expected and reported when analyzed within a rock sample.
Calcification by red algae creates an altered microenvironment potentially distinct in its microbial inhabitants. In addition, coralline-algae-associated-bacteria have been demonstrated to effect macro-scale processes extending beyond the limited magnitude of their niche. The potential role played by CCA-associated microbial community will be examined with respect to its survival in its natural habitat. In addition to 16S analyses of direct fresh algal samples from the reefs, we constructed an array of >200 identified isolates associated with this alga and are prioritizing them for a more detailed functional and metabolic profiling, towards clarification of their roles and importance for N. brassica-florida succession.
On the personal level, this project combines two of my most favorite things - the ocean and microbes.
Alumni
Post Docs
David Bonfil
Eduardo Marco
Flor Martinez
Judy Lieman-Hurwitz
Ilana Berman-Frank
Omer Murik
PhD Students
Drora Zenvirth
Micha Volokita
Yehouda Marcus
Rakefet Schwarz
Michal Ronen-Tarazi
Assaf Vardi
Elza Hallak-Herr
Yael Helman
Dan Tchernov
Daniella Schatz
Gali Shalev-Alon-Malul
Shira Kahlon
Doron Eisenstadt
Yehonatan Bar-Yosef
Moshe Harel
Omer Murik
Maya Heimovich-Dayan
Hagai Raanan
Haim Treves
MSc Students
Rina Ariel
Yossi Rozemberg
Kinneret Pitz-Hermlin
Tammy Bar
Zeev Maor
Shai Kirzner
Rachel Eshkol
Tally Rozenberg
Noa Veinberg
Yariv Harel
Tom Tzur
Yael Keren
Meirav Hadari
Nitzan Garfinkel
Omer Murik
Moshe Harel
Einat Daniel
Maya Haimovitch
Ahinoam Albocher
Gad Weiss
Haim Treves
Nadav Oren
Isaac Kedem