Biology subjects

Pontes, M. H.

Publications and source records attributed to Pontes, M. H..

4 recordsLinked to original sources

bioRxiv2026

Genomic and biochemical contexts determine the physiological role of a horizontally acquired gene

The horizontally acquired mgtC gene from Salmonella enterica confers this bacterium the abilities to survive episodes of magnesium (Mg2+) starvation, and to replicate in mammalian macrophages. The former property allows bacteria to persist in the environment through periods of Mg2+ depletion, whereas the latter allows S. enterica to overcome self-limiting intestinal colonization and cause an invasive systemic infection in susceptible mammalian hosts. Even though the biochemical function of MgtC is not completely understood, this protein is thought to function primarily by preventing the production of toxic levels of Mg2+-chelating adenosine triphosphate (ATP). In the current work, we investigated the physiological roles of mgtC homologs from an array of bacterial species, by probing the processes controlled by this gene during replication in low Mg2+ medium and in macrophages. We determined that MgtC homologs that do not participate in Pi homeostasis during Mg2+ starvation and do not promote intramacrophage replication in their resident species can partake in these processes when expressed in S. enterica. This indicates that the function of this protein is context dependent. Accordingly, we show that the physiological processes affected by S. enterica MgtC vary, depending on whether the bacteria replicate in low Mg2+ medium or inside macrophages. While these results suggest that MgtC is a regulator, they also demonstrate that horizontally acquired genes can assume different roles, depending on the genome and the biochemical context into which they are inserted. ImportanceThe mgtC gene encodes an inner membrane protein that has been horizontally acquired by multiple bacterial species, including several mammalian pathogens. In Salmonella enterica, MgtC promotes replication in mammalian macrophages and allows this bacterium to survive cytoplasmic magnesium (Mg2+) starvation. These phenotypes are thought to result from MgtCs inhibition of Pi metabolism and ATP production, which prevents the accumulation of toxic levels of Mg2+-chelating ATP and disrupts other physiological processes that are strictly dependent on Mg2+, such as ribosome assembly and translation. In the current study, we show that processes that are controlled by MgtC vary with the genetic and biochemical contexts in which this protein is expressed. While establishing a broader role for MgtC as a regulator, our findings illustrate how horizontally acquired regulatory genes can potentiate regulatory interactions, facilitating the evolution of new traits.

microbiology↗

bioRxiv2023

An intracellular phosphorus-starvation signal activates the PhoB/PhoR two-component system in Salmonella enterica

Bacteria acquire P primarily as inorganic orthophosphate (Pi, PO43-). Once internalized, Pi is rapidly assimilated into biomass during the synthesis of ATP. Because Pi is essential, but excessive ATP is toxic, the acquisition of environmental Pi is tightly regulated. In the bacterium Salmonella enterica (Salmonella), growth in Pi-limiting environments activates the membrane sensor histidine kinase PhoR, leading to the phosphorylation of its cognate transcriptional regulator PhoB and subsequent transcription of genes involved in adaptations to low Pi. Pi limitation is thought to promote PhoR kinase activity by altering the conformation of a membrane signaling complex comprised by PhoR, the multicomponent Pi transporter system PstSACB and the regulatory protein PhoU. However, the identity of the low Pi signal and how it controls PhoR activity remain unknown. Here we characterize the PhoB-dependent and independent transcriptional changes elicited by Salmonella in response to P starvation, and identify PhoB-independent genes that are required for the utilization of several organic-P sources. We use this knowledge to identify the cellular compartment where the PhoR signaling complex senses the Pi-limiting signal. We demonstrate that the PhoB and PhoR signal transduction proteins can be maintained in an inactive state even when Salmonella is grown in media lacking Pi. Our results establish that PhoR activity is controlled by an intracellular signal resulting from P insufficiency.

microbiology↗

bioRxiv2020

Limitation of phosphate assimilation maintains cytoplasmic magnesium homeostasis

Phosphorus (P) is an essential component of several core biological molecules. In bacteria, P is mainly acquired as inorganic orthophosphate (Pi). Once in the cytoplasm, Pi is incorporated into adenosine triphosphate (ATP), which exists primarily as a Mg2+ salt. Notably, whereas P is essential, excess of cytosolic Pi hinders growth. Here we demonstrate that cytotoxic effects of excessive Pi uptake result from its assimilation into ATP and subsequent disruption of Mg2+ dependent processes. We show that Salmonella enterica cells experiencing cytoplasmic Mg2+ starvation restrict Pi uptake, thereby limiting the availability of an ATP precursor. This response prevents excessive ATP synthesis, overproduction of ribosomal RNA, chelation of free cytoplasmic Mg2+ and the destabilization of Mg2+-dependent core processes that ultimately hinder bacterial growth and leads to loss of cellular viability. We demonstrate that, even when cytoplasmic Mg2+ is not limiting, excessive Pi uptake leads to increased ATP synthesis, depletion of free cytoplasmic Mg2+, inhibition of translation and growth. Our results establish that bacteria must restrict Pi uptake to prevent the depletion of cytoplasmic Mg2+. Furthermore, they provide a framework to understand the molecular basis of Pi cytotoxicity and reveal a regulatory logic employed by bacterial cells to control P assimilation. ImportancePhosphorus (P) is essential for life. As the fifth most abundant element in living cells, P is required for the synthesis of an array of biological molecules including (d)NTPs, nucleic acids and membranes. Organisms typically acquire environmental P as inorganic phosphate. While essential for growth and viability, excessive intracellular Pi is toxic for both bacteria and eukaryotes. Using the bacterium Salmonella enterica as a model, we demonstrate that Pi cytotoxicity is manifested following its assimilation into ATP, which acts as a chelating agent for intracellular cations, most notably, Mg2+. These results identify physiological processes disrupted by excessive Pi and elucidate a regulatory logic employed by bacteria to prevent uncontrollable P assimilation.

microbiology↗

bioRxiv2020

Conjugal DNA transfer in the maternally inherited symbiont of tsetse flies Sodalis glossinidius

Stable associations between insects and bacterial species are widespread in nature. This is the case for many economically important insects, such as tsetse flies. Tsetse flies are the vectors of Trypanosoma brucei, the etiological agent of African trypanosomiasis--a zoonotic disease that incurs a high socioeconomic cost in endemic regions. Populations of tsetse flies are often infected with the bacterium Sodalis glossinidius. Following infection, S. glossinidius establishes a chronic, stable association characterized by vertical (maternal) and horizontal (paternal) modes of transmission. Due to the stable nature of this association, S. glossinidius has been long sought as a means for the implementation of anti-Trypanosoma paratransgenesis in tsetse flies. However, the lack of tools for the genetic modification of S. glossinidius has hindered progress in this area. Here we establish that S. glossinidius is amenable to DNA uptake by conjugation. We show that conjugation can be used as a DNA delivery method to conduct forward and reverse genetic experiments in this bacterium. This study serves as an important step in the development of genetic tools for S. glossinidius. The methods highlighted here should guide the implementation of genetics for the study of the tsetse-Sodalis association and the evaluation of S. glossinidius-based tsetse fly paratransgenesis strategies. ImportanceTsetse flies are the insect vectors of T. brucei, the causative agent of African sleeping sickness--a zoonotic disease that inflicts a substantial economic cost to a broad region of sub-Saharan Africa. Notably, tsetse flies can be infected with the bacterium S. glossinidius to establish an asymptomatic chronic infection. This infection can be inherited by future generations of tsetse flies allowing S. glossinidius to spread and persist within populations. To this effect, S. glossinidius has been considered as a potential expression platform to create flies which reduce T. brucei stasis and lower overall parasite transmission to humans and animals. However, the efficient genetic manipulation of S. glossinidius has remained a technical challenge due to its complex growth requirements and uncharacterized physiology. Here we exploit a natural mechanism of DNA transfer among bacteria and develop an efficient technique to genetically manipulate S. glossinidius for future studies in reducing trypanosome transmission.

microbiology↗