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Acinetobacter baumannii is outstanding for its ability to cope with low water activities which significantly contributes to its persistence in hospital environments. The vast majority of bacteria are able to prevent loss of cellular water by amassing osmoactive compatible solutes or their precursors into the cytoplasm. One such precursor of an osmoprotectant is choline that is taken up from the environment and oxidized to the compatible solute glycine betaine. Here, we report the identification of the osmotic stress operon betIBA in A. baumannii. This operon encodes the choline oxidation pathway important for the production of the solute glycine betaine. The salt-sensitive phenotype of a betA deletion strain could not be rescued by addition of choline, which is consistent with the role of BetA in choline oxidation. We found that BetA is a choline dehydrogenase but also mediates in vitro the oxidation of glycine betaine aldehyde to glycine betaine. BetA was found to be associated with the membrane and to contain a flavin, indicative for BetA donating electrons into the respiratory chain. The choline dehydrogenase activity was not salt dependent but was stimulated by the compatible solute glutamate.
An exploration of the relationship between recruitment communication and foraging in stingless bees
(2021)
Social information is widely used in the animal kingdom and can be highly adaptive. In social insects, foragers can use social information to find food, avoid danger, or choose a new nest site. Copying others allows individuals to obtain information without having to sample the environment. When foragers communicate information they will often only advertise high-quality food sources, thereby filtering out less adaptive information. Stingless bees, a large pantropical group of highly eusocial bees, face intense inter- and intra-specific competition for limited resources, yet display disparate foraging strategies. Within the same environment there are species that communicate the location of food resources to nest-mates and species that do not. Our current understanding of why some species communicate foraging sites while others do not is limited. Studying freely foraging colonies of several co-existing stingless bee species in Brazil, we investigated if recruitment to specific food locations is linked to 1) the sugar content of forage, 2) the duration of foraging trips, and 3) the variation in activity of a colony from 1 day to another and the variation in activity in a species over a day. We found that, contrary to our expectations, species with recruitment communication did not return with higher quality forage than species that do not recruit nestmates. Furthermore, foragers from recruiting species did not have shorter foraging trip durations than those from weakly recruiting species. Given the intense inter- and intraspecific competition for resources in these environments, it may be that recruiting species favor food resources that can be monopolized by the colony rather than food sources that offer high-quality rewards.
Obligate endoparasitic oomycetes are known to ubiquitously occur in marine and freshwater diatoms, but their diversity is still largely unexplored. Many of these parasitoids are members of the early-diverging oomycete lineages (Miracula, Diatomophthora), others are within the Leptomitales of the Saprolegniomycetes (Ectrogella, Lagenisma) and some have been described in the Peronosporomycetes (Aphanomycopsis, Lagenidium). Even though some species have been recently described and two new genera were introduced (Miracula and Diatomophthora), the phylogeny and taxonomy of most of these organisms remain unresolved. This is contrasted by the high number of sequences from unclassified species, as recently revealed from environmental sequencing, suggesting the presence of several undiscovered species. In this study, a new species of Miracula is reported from a marine centric diatom (Minidiscus sp.) isolated from Skagaströnd harbor in Northwest Iceland. The morphology and life cycle traits of this novel oomycete parasite are described herein, and its taxonomic placement within the genus Miracula is confirmed by molecular phylogeny. As it cannot be assigned to any previously described species, it is introduced as Miracula islandica in this study. The genus Miracula thus contains three described holocarpic species (M. helgolandica, M. islandica, M. moenusica) to which likely additional species will need to be added in the future, considering the presence of several lineages known only from environmental sequencing that clustered within the Miracula clade.
The stem-loop (SL1) is the 5'-terminal structural element within the single-stranded SARS-CoV-2 RNA genome. It is formed by nucleotides 7–33 and consists of two short helical segments interrupted by an asymmetric internal loop. This architecture is conserved among Betacoronaviruses. SL1 is present in genomic SARS-CoV-2 RNA as well as in all subgenomic mRNA species produced by the virus during replication, thus representing a ubiquitous cis-regulatory RNA with potential functions at all stages of the viral life cycle. We present here the 1H, 13C and 15N chemical shift assignment of the 29 nucleotides-RNA construct 5_SL1, which denotes the native 27mer SL1 stabilized by an additional terminal G-C base-pair.
Acinetobacter baumannii is an opportunistic pathogen, which has become a rising threat in healthcare facilities worldwide due to increasing antibiotic resistances and optimal adaptation to clinical environments and the human host. We reported in a former publication on the identification of three phopholipases of the phospholipase D (PLD) superfamily in A. baumannii ATCC 19606T acting in concerted manner as virulence factors in Galleria mellonella infection and lung epithelial cell invasion. This study focussed on the function of the three PLDs. A Δpld1-3 mutant was defect in biosynthesis of the phospholipids cardiolipin (CL) and monolysocardiolipin (MLCL), whereas the deletion of pld2 and pld3 abolished the production of MLCL. Complementation of the Δpld1-3 mutant with pld1 restored CL biosynthesis demonstrating that the PLD1 is implicated in CL biosynthesis. Complementation of the Δpld1-3 mutant with either pld2 or pld3 restored MLCL and CL production leading to the conclusion that PLD2 and PLD3 are implicated in CL and MLCL production. Mutant studies revealed that two catalytic motifs are essential for the PLD3-mediated biosynthesis of CL and MLCL. The Δpld1-3 mutant exhibited a decreased colistin and polymyxin B resistance indicating a role of CL in cationic antimicrobial peptides (CAMPs) resistance.
The genome of the halophilic archaeon Haloferax volcanii encodes more than 40 one-domain zinc finger µ-proteins. Only one of these, HVO_2753, contains four C(P)XCG motifs, suggesting the presence of two zinc binding pockets (ZBPs). Homologs of HVO_2753 are widespread in many euryarchaeota. An in frame deletion mutant of HVO_2753 grew indistinguishably from the wild-type in several media, but had a severe defect in swarming and in biofilm formation. For further analyses, the protein was produced homologously as well as heterologously in Escherichia coli. HVO_2753 was stable and folded in low salt, in contrast to many other haloarchaeal proteins. Only haloarchaeal HVO_2753 homologs carry a very hydrophilic N terminus, and NMR analysis showed that this region is very flexible and not part of the core structure. Surprisingly, both NMR analysis and a fluorimetric assay revealed that HVO_2753 binds only one zinc ion, despite the presence of two ZBPs. Notably, the analysis of cysteine to alanine mutant proteins by NMR as well by in vivo complementation revealed that all four C(P)XCG motifs are essential for folding and function. The NMR solution structure of the major conformation of HVO_2753 was solved. Unexpectedly, it was revealed that ZBP1 was comprised of C(P)XCG motifs 1 and 3, and ZBP2 was comprised of C(P)XCG motifs 2 and 4. There are several indications that ZBP2 is occupied by zinc, in contrast to ZBP1. To our knowledge, this study represents the first in-depth analysis of a zinc finger µ-protein in all three domains of life.
The extraordinary desiccation resistance of the opportunistic human pathogen Acinetobacter baumannii is a key to its survival and spread in medical care units. The accumulation of compatible solute such as glutamate, mannitol and trehalose contributes to the desiccation resistance. Here, we have used osmolarity as a tool to study the response of cells to low water activities and studied the role of a potential inorganic osmolyte, K+, in osmostress response. Growth of A. baumannii was K+-dependent and the K+-dependence increased with the osmolarity of the medium. After an osmotic upshock, cells accumulated K+ and K+ accumulation increased with the salinity of the medium. K+ uptake was reduced in the presence of glycine betaine. The intracellular pools of compatible solutes were dependent on the K+ concentration: mannitol and glutamate concentrations increased with increasing K+ concentrations whereas trehalose was highest at low K+. After osmotic upshock, cells first accumulated K+ followed by synthesis of glutamate; later, mannitol and trehalose synthesis started, accompanied with a decrease of intracellular K+ and glutamate. These experiments demonstrate K+ uptake as a first response to osmostress in A. baumannii and demonstrate a hierarchy in the time-dependent accumulation of K+ and different organic solutes.
Acinetobacter baumannii is outstanding for its ability to cope with low water activities and therefore its adaptation mechanism to osmotic stress. Here we report on the identification and characterization of five different secondary active compatible solute transporters, belonging to the betaine-choline-carnitine transporter (BCCT) family. Our studies revealed two choline-specific and three glycine betaine-specific BCCTs. Activity of the BCCTs was differentially dependent to the osmolality: one choline and one betaine transporter were osmostress-independent. Addition of choline to resting cells of Acinetobacter grown in the presence of the co-substrate choline or with phosphatidylcholine as sole carbon source led to ATP synthesis in the wild type but not in the BCCT quadruple mutant. This indicates that the BCCTs are essential to transport the energy substrate choline. The role of the different BCCTs in osmostress resistance and in metabolic adaptation of A. baumannii to the human host is discussed.
A1AO ATP synthases with a V-type c subunit have only been found in hyperthermophilic archaea which makes bioenergetic analyses impossible due to the instability of liposomes at high temperatures. A search for a potential archaeal A1AO ATP synthase with a V-type c subunit in a mesophilic organism revealed an A1AO ATP synthase cluster in the anaerobic, acetogenic bacterium Eubacterium limosum KIST612. The enzyme was purified to apparent homogeneity from cells grown on methanol to a specific activity of 1.2 U·mg−1 with a yield of 12%. The enzyme contained subunits A, B, C, D, E, F, H, a, and c. Subunit c is predicted to be a typical V-type c subunit with only one ion (Na+)-binding site. Indeed, ATP hydrolysis was strictly Na+-dependent. N,N′-dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis, but inhibition was relieved by addition of Na+. Na+ was shown directly to abolish binding of the fluorescence DCCD derivative, NCD-4, to subunit c, demonstrating a competition of Na+ and DCCD/NCD-4 for a common binding site. After incorporation of the A1AO ATP synthase into liposomes, ATP-dependent primary transport of 22Na+ as well as ΔµNa+-driven ATP synthesis could be demonstrated. The Na+ A1AO ATP synthase from E. limosum is the first ATP synthase with a V-type c subunit from a mesophilic organism. This will enable future bioenergetic analysis of these unique ATP synthases.
Understanding hominin expansions requires the comprehension of movement processes at different scales. In many models of hominin expansion these processes are viewed as being determined by large-scale effects, such as changes in climate and vegetation spanning continents and thousands or even millions of years. However, these large-scale patterns of expansions also need to be considered as possibly resulting from the accumulation of small-scale decisions of individual hominins. Moving on a continental scale may for instance involve crossing a water barrier. We present a generalized agent-based model for simulating the crossing of a water barrier where the agents represent the hominin individuals. The model can be configured to represent a variety of movement modes across water. Here, we compare four different behavioral scenarios in conjunction with a set of water barrier configurations, in which agents move in water by either paddling, drifting, swimming or rafting. We introduce the crossing-success-rate (CSR) to quantify the performance in water crossing. Our study suggests that more focus should be directed towards the exploration of behavioral models for hominins, as directionality may be a more powerful factor for crossing a barrier than environmental opportunities alone. A prerequisite for this is to perceive the opposite shore. Furthermore, to provide a comprehensive understanding of hominin expansions, the CSR allows for the integration of results obtained from small-scale simulations into large-scale models for hominin expansion.