Sporadic diurnal fluctuations of cyanobacterial populations in oligotrophic temperate systems can prevent accurate characterization of change and risk in aquatic systems.

Cyanobacteria increasingly threaten recreational water use and drinking water resources globally. They require dynamic monitoring to account for variability in their distribution arising from diel cycles associated with oscillatory vertical migration. While this has been discussed in marine and eutrophic freshwater contexts, reports of diurnal vertical migration of cyanobacteria in oligotrophic freshwater lakes are scant. Typical monitoring protocols do not reflect these dynamics and frequently focus only on surface water sampling approaches, and either ignore sampling time or recommend large midday timeframes (e.g., 10AM-3PM), thereby preventing accurate characterization of cyanobacterial community dynamics. To evaluate the impact of diurnal migrations and water column stratification on cyanobacterial abundance and composition, communities were characterized in a shallow well-mixed lake interconnected to a thermally stratified lake in the Turkey Lakes Watershed (Ontario, Canada) using amplicon sequencing of the 16S rRNA gene across a multi-time point sampling series in 2018 and 2022. This work showed that cyanobacteria are present in oligotrophic lakes and their community structure varies (i) diurnally, (ii) across the depth of the water column, (iii) interannually within the same lake and (iv) between different lakes that are closely interconnected within the same watershed. It underscored the need for integrating multi-timepoint, multi-depth discrete sampling guidance into lake and reservoir monitoring programs to describe cyanobacteria community dynamics and signal change to inform risk management associated with the potential for cyanotoxin production. Ignoring variability in cyanobacterial community dynamics (such as that reported herein) and reducing sample numbers can lead to a false sense of security and missed opportunities to identify and mitigate changes in trophic status and associated risks such as toxin or taste and odor production, especially in sensitive, oligotrophic systems.

Interspecific differences in the effects of masking and distraction on anti-predator behavior in suburban anthropogenic noise.

Predation is a common threat to animal survival. The detection of predators or anti-predator communication signals can be disrupted by anthropogenic noise; however, the mechanism by which responses are affected is unclear. Masking and distraction are the two hypotheses that have emerged as likely explanations for changes in behavior in noise. Masking occurs when the signal and noise fall within the same sensory domain; noise overlapping the energy in the signal reduces signal detection. Distraction can occur when noise in any sensory domain contributes to a greater cognitive load, thereby reducing signal detection. Here, we used a repeated measures field experiment to determine the relative contributions of masking and distraction in mediating reduced anti-predator responses in noise. We recorded the approaches and vocalizations of black-capped chickadees (Poecile atricapillus), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis) to both visual and acoustic cues of predator presence, either with or without simultaneous exposure to anthropogenic noise. Titmice increased their calling to both visual and acoustic cues of predator presence. However, there was no significant effect of noise on the calling responses of titmice regardless of stimulus modality. Noise appeared to produce a distraction effect in chickadees; however, this effect was small, suggesting that chickadees may be relatively unaffected by low levels of anthropogenic noise in suburban environments. White-breasted nuthatch calling behavior was affected by the interaction of the modality of the predator stimulus and the noise condition. Nuthatches had a delayed response to the predator presentations, with a greater calling rate following the presentation of the acoustic stimulus in quiet compared to the presentation of the acoustic stimulus in noise. However, there was no difference in calling rate between the quiet and noise conditions for the visual stimulus. Together this suggests that even moderate levels of noise have some masking effect for white-breasted nuthatches. We suggest that the mechanisms through which noise influences anti-predator behavior may depend on the social roles, foraging ecology and auditory capabilities of each species.

Cofilin-Membrane Interactions: Electrostatic Effects in Phosphoinositide Lipid Binding.

The actin cytoskeleton interacts with the cell membrane primarily through the indirect interactions of actin-binding proteins such as cofilin-1. The molecular mechanisms underlying the specific interactions of cofilin-1 with membrane lipids are still unclear. Here, we performed coarse-grain molecular dynamics simulations of cofilin-1 with complex lipid bilayers to analyze the specificity of protein-lipid interactions. We observed the maximal interactions with phosphoinositide (PIP) lipids, especially PIP2 and PIP3 lipids. A good match was observed between the residues predicted to interact and previous experimental studies. The clustering of PIP lipids around the membrane bound protein leads to an overall lipid demixing and gives rise to persistent membrane curvature. Further, through a series of control simulations, we observe that both electrostatics and geometry are critical for specificity of lipid binding. Our current study is a step towards understanding the physico-chemical basis of cofilin-PIP lipid interactions.

Caveolin induced membrane curvature and lipid clustering: two sides of the same coin?

Caveolin-1 (cav-1) is a multi-domain membrane protein that is a key player in cell signaling, endocytosis and mechanoprotection. It is the principle component of cholesterol-rich caveolar domains and has been reported to induce membrane curvature. The molecular mechanisms underlying the interactions of cav-1 with complex membranes, leading to modulation of membrane topology and the formation of cholesterol-rich domains, remain elusive. In this study, we aim to understand the effect of lipid composition by analyzing the interactions of cav-1 with complex membrane bilayers comprised of about sixty lipid types. We have performed a series of coarse-grain molecular dynamics simulations using the Martini force-field with a cav-1 protein construct (residue 82-136) that includes the membrane binding domains and a palmitoyl tail. We observe that cav-1 induces curvature in this complex membrane, though it is restricted to a nanometer length scale. Concurrently, we observe a clustering of cholesterol, sphingolipids and other lipid molecules leading to the formation of nanodomains. Direct microsecond timescale interactions are observed for specific lipids such as cholesterol, phosphatidylserine and phosphatidylethanolamine lipid types. The results indicate that there is an interplay between membrane topology and lipid species. Our work is a step toward understanding how lipid composition and organization regulate the formation of caveolae, in the context of endocytosis and cell signaling.

Sphingomyelin Effects in Caveolin-1 Mediated Membrane Curvature.

The caveolin-1 (cav-1) protein is an integral component of caveolae and has been reported to colocalize with cholesterol and sphingomyelin-rich curved membrane domains. Here, we analyze the molecular interactions between cav-1 and sphingomyelin containing bilayers using a series of coarse-grain simulations, focusing on lipid clustering and membrane curvature. We considered a palmitoylated-cav-1 construct interacting with phospholipid/cholesterol membranes with asymmetrically distributed sphingomyelin, varying between 5 and 15% in total. We observe that cav-1 binds to the intracellular leaflet and induces a small positive curvature in the leaflet to which it is bound and an opposing negative curvature in the extracellular leaflet. Both cholesterol and sphingomyelin are observed to cluster in cav-1 bound membranes, mainly in the extracellular leaflet. Due to their negative spontaneous curvature, clustering of cholesterol and sphingomyelin facilitates membrane curvature such that the extent of either cholesterol or sphingomyelin clustering is dependent on the curvature induced. Our results suggest that cav-1 binding induces concentration-dependent curvature effects in sphingomyelin-rich membranes. Overall, our work is an important step in understanding the molecular basis of curvature and lipid clustering in cav-1 bound cellular membranes.

Interplay between Membrane Curvature and Cholesterol: Role of Palmitoylated Caveolin-1.

Caveolin-1 (cav-1) is an important player in cell signaling and endocytosis that has been shown to colocalize with cholesterol-rich membrane domains. Experimental studies with varying cav-1 constructs have suggested that it can induce both cholesterol clustering and membrane curvature. Here, we probe the molecular origin of membrane curvature and cholesterol clustering by cav-1 by using coarse-grain molecular dynamics simulations. We have performed a series of simulations of a functionally important cav-1 construct, comprising the membrane-interacting domains and a C-terminal palmitoyl tail. Our results suggest that cav-1 is able to induce cholesterol clustering in the membrane leaflet to which it is bound as well as the opposing leaflet. A positive membrane curvature is observed upon cav-1 binding in cholesterol-containing bilayers. Interestingly, we observe an interplay between cholesterol clustering and membrane curvature such that cav-1 is able to induce higher membrane curvature in cholesterol-rich membranes. The role of the cav-1 palmitoyl tail is less clear and appears to increase the membrane contacts. Further, we address the importance of the secondary structure of cav-1 domains and show that it could play an important role in membrane curvature and cholesterol clustering. Our work is an important step toward a molecular picture of caveolae and vesicular endocytosis.

Gustatory function in chronic otitis media (mucosal type) before and after tympanoplasty.

Chronic inflammation in the middle ear may result in functional impairment of the chorda tympani nerve, which carries taste from the anterior two-thirds of the tongue. This may lead to impaired taste sensation. Timely intervention and adequate disease clearance may help the chorda tympani nerve to recover. Gustatory function of 107 patients who underwent Tympanoplasty for Chronic otitis media (mucosal type) was evaluated in a cohort of Indian patients. To compare the preoperative and postoperative gustatory function in these patients taste scores were documented preoperatively, and at 6 weeks and 3 months postoperatively, in an effort to document taste function improvement after disease clearance. The taste scores thus obtained were recorded and analyzed. A significant improvement in taste threshold postoperatively in comparison to the preoperative taste scores (p = 0.001) was found. It was observed that age of the patient and duration of illness have a significant impact on the recovery of taste function. Our study suggests that taste perception improves over a period of time after successful tympanoplasty in patients with chronic otitis media (mucosal type).

Posterior arm compartment syndrome after a combined supracondylar humeral and capitellar fractures in an adolescent: a case report.

BACKGROUND: Supracondylar humeral fractures in children are common, with associated bony injuries typically being fractures of the forearm or distal radius. To our knowledge, a combined supracondylar humeral fracture associated with a Hahn-Steinthal capitellar fracture has not been reported earlier. Similarly, posterior arm compartment syndrome is extremely rare, with most instances having occurred after chronic compression and bleeding into the compartments from anticoagulation, direct trauma including crush, or tendon ruptures. Only 2 cases have been reported after a fracture of the humerus. One of these described fractures was localized to a distal shaft and the other involved the surgical neck. No cases have been reported in children, nor have any been reported after a supracondylar humeral fracture. METHODS: In this case report, we describe a patient who presented with an ipsilateral Wilkins type-3A supracondylar humeral fracture, Hahn-Steinthal capitellar fracture, Salter-Harris II distal radius fracture, and posterior arm compartment syndrome. RESULTS: The patient was taken to the operative room for closed reduction and percutaneous pinning of the radius fracture with open reduction, internal fixation of the distal humeral fractures. Elevated compartment pressure measurements were anticipated because of the nature of the injuries. After fixation of the fractures, the mobile wad, volar, and dorsal compartments measured 9, 9, and 8 mm Hg, respectively. The absolute pressure in the posterior arm compartment was measured multiple times in different locations ranging from 34 to 39 mm Hg. The patient's blood pressure throughout the case averaged 115/65 mm Hg. A diagnosis of posterior arm compartment syndrome was confirmed and the fascia was released. CONCLUSIONS: Our patient ultimately suffered 2 uncommon injuries involving the arm. She sustained a complex fracture of the distal humerus with an extension type supracondylar fracture, a separate Hahn-Steinthal capitellar fracture, and isolated posterior arm compartment syndrome. This is an unusual case that required specialized care and follow-up. LEVEL OF EVIDENCE: Level IV.