Biology subjects

Bulzu, P.-A.

Publications and source records attributed to Bulzu, P.-A..

6 recordsLinked to original sources

bioRxiv2025

Season-specific responses of freshwater ciliate communities to top-down and bottom-up experimental manipulations

In aquatic microbial food webs, ciliates represent an important trophic link in the energy transfer from prokaryotes, algae, and heterotrophic nanoflagellates (HNF) to higher trophic levels. However, the trophic role of abundant small ciliates (< 20 {micro}m) is not clearly understood. To unveil their trophic linkages, we conducted two experiments manipulating both top-down and bottom-up controlling factors, thus modulating the trophic cascading and bacterial prey availability for protists during contrasting spring and summer seasons with samples collected from a freshwater meso-eutrophic reservoir. Water samples were size fractionated, to modify food web complexity, i.e. 10-{micro}m, 20-{micro}m and unfiltered control and amended with bacterial prey additions. The samples were analyzed by morphological and sequencing techniques. The bacterial amendments triggered strong ciliate growth following the peaks of HNF in the 10-{micro}m and 20-{micro}m treatments, reflecting a trophic cascading from HNF to raptorial prostome ciliates (Balanion planctonicum and Urotricha spp.) in spring. In summer, HNF and ciliates peaked simultaneously, suggesting the important trophic cascade from bacteria to bacterivorous scuticociliates (Cyclidium glaucoma and Cinetochilum margaritaceum) and HNF. In spring, unfiltered treatments showed stronger ciliate top-down control by zooplankton than in summer. The sequence analysis revealed season-specific manipulation-induced shifts in ciliate communities and their large cryptic diversity. However, morphological and molecular analyses also revealed considerable discrepancies in the abundance of major ciliate taxa. The ciliate communities responded to our experimental manipulations in season-specific fashion, thereby highlighting the different roles of ciliates as an intermediate trophic link between prokaryotes and higher trophic levels. IMPORTANCECiliates are an important trophic link in aquatic microbial food webs. In this study, we used the food web manipulation techniques to reveal their complex trophic interactions during seasonally different plankton scenarios occurring in spring and summer. Manipulating top-down controlling factors (grazing pressure of micro- and metazooplankton grazers) and bottom-up factors (an availability of bacterial prey) shaped distinctly the complexity and dynamics of natural plankton communities and thus yielded significant changes in ciliate community dynamics. The experimentally simplified plankton and ciliate communities responded to our manipulations in season-specific fashions, reflected in different roles of ciliates as an intermediate trophic link between prokaryotes and higher trophic levels. This study also demonstrates that the combination of morphological and molecular analyses is essential for providing robust and ecologically meaningful results due to the reliability in quantifying the major ciliate taxa and their trophic role.

ecology↗

bioRxiv2023

Rickettsiales' deep evolutionary history sheds light on the emergence of intracellular lifestyles

Ancient bacteria largely lived and flourished as free-living cells till the rise of eukaryotes triggered their adaptation to a new habitat: the intracellular milieu. Rickettsiales bacteria are the most prevalent intracellular microorganisms discovered and the culprits behind some of mankinds worst pestilential diseases. Here, we show that intracellularity is not a defining feature of the group and describe the eco-evolutionary processes that transformed harmless free-living bacteria into obligate intracellular symbionts and parasites. We found that the evolution of free-living lineages towards enhanced cross-feeding interactions with microbial eukaryotes trapped them in a nutritional bind to their trophic partners. We discovered that the oldest Rickettsiales lineages are the closest relatives to modern eukaryotes and are enriched in proteins predicted to have been present in the mitochondrial ancestor. This study not only opens avenues for the detection and surveillance of emerging diseases but also expands our understanding of the origins of complex life. One-Sentence SummaryCross-feeding interactions shaped Rickettsiales genomic architectures along the parasite/free-living spectrum

microbiology↗

bioRxiv2021

Quorum sensing signals from epibiont mediate the induction of bioactive peptides in mat-forming cyanobacteria Nostoc

The regulation of oligopeptides production is essential in understanding their ecological role in complex microbial communities including harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the microbial community harboured as epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. Herein, we present insight into the role of a bacterial epibiont in regulating production of cyanobacterial oligopeptides microviridins, well-known elastase inhibitors with presumed anti-grazing effects, in an ecologically important cyanobacterial genus Nostoc. Heterologous expression and identification of specific signal molecules from the epibiont suggest the role of a quorum sensing-based interaction. Further, physiological experiments show an increase in microviridin production without affecting cyanobacterial growth and photosynthetic activity. Simultaneously, oligopeptides presenting a selective inhibition pattern provide support for their specific function in response to the presence of cohabitant epibionts. Thus, the chemical interaction revealed in our study provides an example of an interspecies signalling pathway monitoring the bacterial flora around the cyanobacterial filaments and induction of intrinsic species-specific metabolic responses. IMPORTANCEThe regulation of cyanopeptide production beyond microcystin is essential to understand their ecological role in complex microbial communities, e.g. harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. The frequency of cyanopeptide occurrence also demonstrates the need to understand the contribution of cyanobacterial peptides to the overall biological impact of cyanopeptides on aquatic organisms and vertebrates including humans. Our results shed light on the epibiont control of cyanopeptide production via quorum sensing mechanisms and we posit that such mechanisms may be widespread in natural cyanobacterial bloom community regulation.

microbiology↗

bioRxiv2021

Heliorhodopsin evolution is driven by photosensory promiscuity in monoderms

The ability to harness Suns electromagnetic radiation by channeling it into high-energy phosphate bonds empowered microorganisms to tap into a cheap and inexhaustible source of energy. Lifes billion-years history of metabolic innovations led to the emergence of only two biological complexes capable of harvesting light: one based on rhodopsins and the other on (bacterio)chlorophyll. Rhodopsins encompass the most diverse and abundant photoactive proteins on Earth and were until recently canonically split between type-1 (microbial rhodopsins) and type-2 (animal rhodopsins) families. Unexpectedly, the long-lived type-1/type-2 dichotomy was recently amended through the discovery of heliorhodopsins (HeRs) (Pushkarev et al. 2018), a novel and exotic family of rhodopsins (i.e. type-3) that evaded recognition in our current homology-driven scrutiny of lifes genomic milieu. Here, we bring to resolution the debated monoderm/diderm occurrence patterns by conclusively showing that HeR distribution is restricted to monoderms. Furthermore, through investigating protein domain fusions, contextual genomic information, and gene co-expression data we show that HeRs likely function as generalised light-dependent switches involved in the mitigation of light-induced oxidative stress and metabolic circuitry regulation. We reason that HeRs ability to function as sensory rhodopsins is corroborated by their photocycle dynamics (Pushkarev et al. 2018) and that their presence and function in monoderms is likely connected to the increased sensitivity to light-induced damage of these organisms (Maclean et al. 2009).

microbiology↗

bioRxiv2019

Visualization of Loki- and Heimdallarchaeia (Asgardarchaeota) by fluorescence in situ hybridization and catalyzed reporter deposition (CARD-FISH)

Metagenome-assembled genomes (MAGs) of Asgardarchaeota are starting to be recovered from a variety of habitats, broadening their environmental distribution and providing access to the genetic makeup of this archaeal lineage. Despite their singular phylogenetic position at the base of the eukaryotic tree of life, the morphology of these bewildering organisms remains a mystery. In order to visualize this elusive group, we applied a combination of CARD-FISH and epifluorescence microscopy on coastal hypersaline sediment samples, using specifically designed CARD-FISH probes for Heimdallarchaeia and Lokiarchaeia lineages and provide the first visual evidence for both these groups. Here, we show that while Heimdallarchaeia are characterized by a uniform cellular morphology typified by central DNA localization, Lokiarchaeia display a plethora of shapes and sizes that likely reflect their broad phylogenetic diversity and ecological distribution.

microbiology↗

bioRxiv2018

The sunlit microoxic niche of the archaeal eukaryotic ancestor comes to light

Recent advances in phylogenomic analyses and increased genomic sampling of uncultured prokaryotic lineages brought compelling evidence in support of the emergence of eukaryotes from within the Archaea domain of life. The discovery of Asgardaeota archaea and their recognition as the closest extant relative of eukaryotes fuelled the revival of a decades-old debate regarding the topology of the tree of life. While it is apparent that Asgardaeota encode a plethora of eukaryotic-specific proteins (the highest number identified to date in prokaryotes), the lack of genomic information and metabolic characterization has precluded inferences about their lifestyles and the metabolic landscape that may have favoured the emergence of the hallmark eukaryotic subcellular architecture. Here, we use advanced phylogenetic analyses to infer the deep ancestry of eukaryotes and genome-scale metabolic reconstructions to shed light on the metabolic milieu of the closest archaeal eukaryotic ancestors discovered till date. In doing so, we: i) generate the largest Asgardaeota genomic dataset available so far, ii) describe a new clade of rhodopsins encoded within the recovered genomes, iii) provide unprecedented evidence for mixotrophy within Asgardaeota, iv) present first-ever proofs that the closest extant archaeal relatives to all eukaryotes (Heimdallarchaeia) have microoxic lifestyles with aerobic metabolic pathways unique among Archaea (i.e. kynurenine pathway) and v) generate the first images of Asgardaeota.

microbiology↗