Högskolan i Skövde

Introduction: Salivary mucin MUC5B has been suggested to support eubiosis in early oral biofilms by regulating the attachment of commensals, while downregulating dysbiotic activities related to dental caries development, such as microbial carbohydrate transport and metabolism.

Methods: To investigate how the metabolism of glucose, a potential driver for dental caries, in early mono- and dual-species biofilms of oral Actinomyces naeslundii and Streptococcus gordonii clinical isolates was affected by the presence of the complex salivary mucin MUC5B, this study employed nuclear magnetic resonance (NMR)-based metabolomics with the interpretation of network integration.

Results and discussion: MUC5B reduced early attachment in the presence of glucose compared with uncoated surfaces but maintained even species distribution. This suggests that MUC5B may represent an innate mechanism to regulate biofilm eubiosis by supporting early coadhesion while regulating total biomass. All annotated metabolites were intermediates in either carbohydrate metabolism, pyruvate conversion, or amino acid metabolism, which was not unexpected in biofilm glucose metabolomes from two saccharolytic species since pyruvate conversion represents a junction point between glycolysis and amino acid metabolic chains. The 10 metabolites present in all early biofilms represent a core metabolome shared by A. naeslundii and S. gordonii. Such core metabolomes can be used to detect deviations in future studies. Significant differences in metabolite abundance elicited by the presence of MUC5B were also detected. In early biofilms where they were each present, pyruvate, ethanol, and metabolite 134 were present in significantly higher abundance in the presence of 25% MUC5B with 20 mM glucose (MUC5B + G) compared with a physiologic buffer with 20 mM glucose (PBS + G), while metabolites 84, 97, and sarcosine were present at significantly lower abundance. Metabolite 72 was unique to biofilms grown in MUC5B + G, and eight unannotated metabolites were unique to biofilms grown in PBS + G. A pathway enrichment analysis of the metabolites that were differently expressed in early A. naeslundii, S. gordonii, and dual-species biofilms grown with 20 mM glucose with or without MUC5B showed that pyruvate metabolism was significantly over-represented. Studying the metabolic interactions between commensal members of oral biofilms and modulatory effects of host factors such as glycoproteins in saliva during the metabolism of substrates that are potential drivers of dysbiosis, such as glucose, is essential to understand the roles of oral microbial ecosystems in oral health and disease.

Winter mortality of honeybees (Apis mellifera) is one of the biggest challenges in beekeeping, with significant economic andecological consequences. Although most Swedish beekeepers overwinter their bees on sugar water to maximize honey harvest, there is a lack of scientific studies investigating how this practice affects bee health compared to overwintering on their own honey. Today, it remains unclear how different overwintering diets influence the gut microbiota of honeybees and their ability to survive the long Swedish winter. In general, scientific studies on winter diets are rare, especially those focusing on the microbiome and subsequent spring survival. In this study, we investigated how the overwintering diet affects the gut microbiota as well as the health and survival of the Swedish honeybees. We 1) analyzed the gut microbiome of Swedish honeybees (Apis mellifera) colonies using third-generation sequencing (Oxford Nanopore Technologies), 2) compared the bacterial composition and relative abundance across the three different diets (honey, sugar, honey-sugar mixture) over one winter season (October 2024 to March 2025) and 3) examined whether the overwintering diets affect the bees´ health condition at the beginning of the new season. To assess the bee health, we focused on visible signs of diarrhea and monitored colony development during the spring, including brood and drone development as well as their pollen collection (April to June 2025). Our first preliminary results showed that the microbiome differs depending on the food the honeybees have eaten during overwintering. In addition to characterizing data on the gut microbiome of the Swedish honeybees, this study aims to identify the optimal winter diet to support successful overwintering. Winter mortality is costly, both for the professional beekeeper and the recreational beekeeper, and even a delayed spring start can negatively impact colony productivity. That is why we also analyzed the mixed diet - consisting of honey and sugar - as an interesting alternative, which may help future beekeepers to cultivate honeybee colonies with a healthier and more diverse microbiome flora, which can support the bees’ fitness and resilience at the onset of the new season.

Honeybee drones’ only known task is to mate with a virgin queen. Apart from their mating behaviour, their ecology has been little studied, especially in comparison to honeybee females. Previous knowledge is primarily based on short-term direct observations at single experimental hives, rarely, if ever, addressing the effect of drones’ genetic origin. Here, Radio Frequency Identification Technology was utilised to gather drone and worker bee lifetime data of Apis mellifera mellifera and Apis mellifera x (hybrid Buckfast) colonies over one mating season (spring and summer) with the ultimate goal to investigate differences at subspecies level. This technique enabled continuous monitoring of tagged bees at the hive entrance and recording of individuals’ movement directions. The results confirmed that spring-born drones survive longer than summer-born drones and that they generally live longer than worker bees. Drones’ peak activity occurred in the afternoon while worker bees showed more even activity levels throughout the day. Earlier orientation flights than usually reported for drones were observed. In summer, mating flights were practiced before reaching sexual maturity (at 12 days of age). Differences were found between Apis m. mellifera and Buckfast drones, where Apis m. mellifera showed later drone production in spring, but significantly earlier first activities outside the hive in summer and a later peak in diurnal activity. Additionally, Apis m. mellifera flew more in higher light intensities and windy conditions and performed significantly longer flights than Buckfast drones. The observed differences in drone ecology indicate the existence of a local adaptation of the native subspecies Apis m. mellifera to environmental conditions in southwestern Sweden.

Honungsbiets naturliga hemvist är framförallt det ihåliga trädet, det känner nog nästan alla till, kanske också av egen erfarenhet.

Little information exists on the history and ecology of free-living colonies of European honey bees (Apis mellifera L.) in Europe, including its dark north-western subspecies (Apis mellifera mellifera). Our aim was to investigate the presence of colonies of free-living, native honey bees (A. m. mellifera) during the last two centuries in Sweden. For this we examined systematic interviews of beekeepers (176 answers from 158 questionnaires) performed in the years 1928–1981, with information dating back to the early 1800s. An overwhelming majority of answers (96%) confirmed the past presence of free-living colonies of honey bees in Sweden. While some stated that free-living colonies were simply absconded swarms from managed hives, the majority of interviewees (69%) believed that free-living colonies were of a truly wild origin. A decreasing trend in first-hand accounts of free-living colonies suggests that free-living populations underwent a dramatic decline at the end of the 19th century. This was also expressed in words by many interviewees, who in 14 cases stated that the loss of old forests and tree-cavity nest sites at the end of the 1800s was the primary cause of the decline. Direct accounts of perennial, free-living colonies, combined with detailed descriptions of the collection of large free-living colonies and/or wild honey, is strong evidence of free-living honey bees being well adapted to winter survival. These accounts contradict the officially supported view that the honey bee is a recently imported, domesticated, non-native species in Sweden. The results give a scientific underpinning and provide inspiration for the restoration of native forests which could facilitate populations of free-living colonies of A. m. mellifera exposed to natural selection. This could potentially lead to its return as a fully wild species. In an uncertain future, allowing for a natural lifestyle could increase resilience and reinstate characteristics that are otherwise lost in honey bees due to the increasing effects of artificial trait selection.

Video recording is a common method to study animal behaviour. In honey bee studies, short video-recordings are often used to learn more about a behaviour, but rarely used for their quantification. Standard methods for observing bee behaviour involve behavioural assays or direct observation of a limited subset of marked bees within an observation hive. This means that behaviour at the hive entrance may be overlooked. Here we describe a 4-camera set up for the study of behaviour at hive entrances. With minimal disturbance, we were able to record and quantify all previously described behaviours (9 in total - including self-grooming in drones) on and around the hive entrance. We briefly discuss the general feasibility of video footage and the relative frequency of each observed behaviour. Our conclusion is that video footage is a useful and perhaps overlooked method for unbiased quantification and comparisons of bee behaviour at the hive entrance. With this paper we are publishing some example short video-recordings as online supplementary material for educational purposes.

Honey bees are currently facing mounting pressures that have resulted in population declines in many parts of the world. In northern climates winter is a bottleneck for honey bees and a thorough understanding of the colonies’ ability to withstand the winter is needed in order to protect the bees from further decline. In this study the influence of weather variables on colony weight loss was studied over one winter (2019–2020) in two apiaries (32 colonies in total) in southwestern Sweden with weather stations recording wind and temperature at 5-min intervals. Three subspecies of honey bees and one hybrid were studied: the native Apis mellifera mellifera, the Italian A. m. ligustica, the Carniolan A. m. carnica and the hybrid Buckfast. Additionally, we recorded Varroa mite infestation. To analyze factors involved in resource consumption, three modelling approaches using weather and weight data were developed: the first links daily consumption rates with environmental variables, the second modelled the cumulative weight change over time, and the third estimated weight change over time taking light intensity and temperature into account. Weight losses were in general low (0.039 ± 0.013kg/day and colony) and comparable to southern locations, likely due to an exceptionally warm winter (average temperature 3.5°C). Weight losses differed only marginally between subspecies with indications that A. m. mellifera was having a more conservative resource consumption, but more studies are needed to confirm this. We did not find any effect of Varroa mite numbers on weight loss. Increased light intensity and temperature both triggered the resource consumption in honey bees. The temperature effect on resource consumption is in accordance with the metabolic theory of ecology. The consequences of these findings on honey bee survival under predicted climate changes, is still an open question that needs further analysis.