Expression and Characterization of a β-Galactosidase from the Pacific Oyster, Crassostrea gigas, and Evaluation of Strategies for Testing Substrate Specificity

β-Galactosidases (EC 3.2.1.23) are exoglycosidases that catalyze the cleavage of glycoconjugates with terminal β-D-galactose residues in β1,3-, β1,4- or β1,6-linkage. Although this family of exoglycosidases has been extensively studied in vertebrates, plants, yeast, and bacteria, little information is available for mollusks. Mollusks are a diverse and highly successful group of animals that play many different roles in their ecosystems, including filter feeders and detritivores. Here, the first β-galactosidase from the Pacific oyster, Crassostrea gigas was discovered, biochemically characterized, and compared to our previously characterized slug enzyme from Arion vulgaris (UniProt Ref. Nr.: A0A0B7AQJ9). Overall, the mussel enzyme showed similar biochemical parameters to the snail enzyme. The enzyme from C. gigas was most active in an acidic environment (pH 3.5) and at a reaction temperature of 50 °C. Optimal storage conditions were up to 37 °C. In contrast to the enzyme from A. vulgaris, the supplementation of cations (Ni2+, Co2+, Mn2+, Mg2+, Ca2+, Cu2+, Ba2+) increased the activity of the enzyme from C. gigas. Substrate specificity studies of the β-galactosidases from the mussel, C. gigas, and the slug, A. vulgaris, revealed activity towards terminal β1,3- and β1,4-linked galactose residues for both enzymes. Using the same substrates in labeled and unlabeled form, we were able to detect the effect of labeling on the β-galactosidase activity using MALDI-TOF MS, HPTLC, and HPLC. While lactose was cleaved by the enzymes in an unlabeled or labeled state, galacto-N-biose was not cleaved as soon as a 2-amino benzoic acid label was added. In this study we present the biochemical characterization of the first recombinantly expressed β-galactosidase from the Pacific oyster, C. gigas, and we compare different analytical methods for the determination of β-galactosidase activity using the enzyme from C. gigas and A. vulgaris.

Identification, Characterization, and Expression of a β-Galactosidase from Arion Species (Mollusca)

β-Galactosidases (β-Gal, EC 3.2.1.23) catalyze the cleavage of terminal non-reducing β-D-galactose residues or transglycosylation reactions yielding galacto-oligosaccharides. In this study, we present the isolation and characterization of a β-galactosidase from Arion lusitanicus, and based on this, the cloning and expression of a putative β-galactosidase from Arion vulgaris (A0A0B7AQJ9) in Sf9 cells. The entire gene codes for a protein consisting of 661 amino acids, comprising a putative signal peptide and an active domain. Specificity studies show exo- and endo-cleavage activity for galactose β1,4-linkages. Both enzymes, the recombinant from A. vulgaris and the native from A. lusitanicus, display similar biochemical parameters. Both β-galactosidases are most active in acidic environments ranging from pH 3.5 to 4.5, and do not depend on metal ions. The ideal reaction temperature is 50 °C. Long-term storage is possible up to +4 °C for the A. vulgaris enzyme, and up to +20 °C for the A. lusitanicus enzyme. This is the first report of the expression and characterization of a mollusk exoglycosidase.

A discovery of two new Tetrahymena species parasitizing slugs and mussels: morphology and multi-gene phylogeny of T. foissneri sp. n. and T. unionis sp. n

The presence of parasitic ciliates of the hymenostome genus Tetrahymena was examined in 150 mollusks belonging to six bivalve and 13 gastropod species in Slovakia, Central Europe. Tetrahymenids were detected only in two species, viz., in the invasive Lusitanian slug (Arion vulgaris) and in the native swollen river mussel (Unio tumidus). Although only 10.52% of the examined mollusk taxa were positive, their Tetrahymena infections were very intensive accounting for several hundreds of ciliates per host. Phylogenetic analyses of the 16S and 18S rRNA genes as well as of the barcoding region of the gene encoding for cytochrome c oxidase subunit I revealed that both isolates represent new taxa, T. foissneri sp. n. and T. unionis sp. n. The former species belongs to the 'borealis' clade and its nearest relative is T. limacis, a well-known parasite of slugs and snails. Besides molecular data, T. foissneri can be distinguished from T. limacis also morphologically by the body shape of the parasitic-phase form, dimensions of micronuclei, and the silverline system. On the other hand, T. unionis was classified within the 'paravorax' clade along with T. pennsylvaniensis, T. glochidiophila, and T. nigricans. Although these four species are genetically distinct, T. unionis could be morphologically separated only from T. nigricans by body shape and size. The present study suggests that both aquatic and terrestrial mollusks represent interesting hosts for the discovery of novel Tetrahymena lineages.

Detection of Crenosoma spp., Angiostrongylus vasorum and Aelurostrongylus abstrusus in Gastropods in Eastern Austria

Canine and feline cardiorespiratory parasites are of utmost relevance in veterinary medicine. Key epizootiological information on major pet metastrongyloids, i.e., Angiostrongylus vasorum and Crenosoma vulpis infecting dogs, and Aelurostrongylus abstrusus and Troglostrongylus brevior infecting cats, is missing from Austria. This study investigated their occurrence in 1320 gastropods collected in the Austrian provinces of Styria, Burgenland, Lower Austria, and in metropolitan Vienna. Metastrongyloid larvae were microscopically detected in 25 samples, and sequence analysis confirmed the presence of metastrongyloids in nine samples, i.e., A. vasorum in one slug (Arion vulgaris) (0.07%), C. vulpis in five slugs (one Limax maximus and four A. vulgaris) (0.4%), A. abstrusus in two A. vulgaris (0.17%), and the hedgehog lungworm Crenosoma striatum was detected in one A. vulgaris. The present study confirms the enzooticity of major cardiorespiratory nematodes in Austria and that canine and feline populations are at risk of infection.

Occurrence of canine and feline lungworms in Arion vulgaris in a park of Vienna: First report of autochthonous Angiostrongylus vasorum, Aelurostrongylus abstrusus and Troglostrongylus brevior in Austria

So far, neither the feline lungworms Aelurostrongylus abstrusus and Troglostrongylus brevior nor the canine lungworm Angiostrongylus vasorum was reported in wildlife or intermediate hosts from Austria. The slug Arion vulgaris represents an invasive species in Europe and serves as intermediate host for several lungworm species. This study aimed to analyse the occurrence of metastrongyloid lungworm larvae in slugs in Vienna, Austria. Therefore, 193 A. vulgaris were collected in the central Prater park in summer 2016. Specimens were artificially digested, analysed microscopically for lungworm larvae, and species were confirmed via PCR and sequencing. Out of 193, five slugs were positive to lungworms (2.6%), one for A. vasorum, two for A. abstrusus (genotypes A and B) and one for T. brevior, and one slug had a mixed infection of A. abstrusus and T. brevior larvae. The current study is the first evidence on the endemicity of these metastrongyloid lungworm species in Austria.

Occurrence of the invasive Spanish slug in gardens: can a citizen science approach help deciphering underlying factors?

BACKGROUND

The Spanish slug (Arion vulgaris, also known as A. lusitanicus) is considered one of the most invasive species in agriculture, horticulture and private gardens all over Europe. Although this slug has been problematic for decades, there is still not much known about its occurrence across private gardens and the underlying meteorological and ecological factors. One reason for this knowledge gap is the limited access of researchers to private gardens. Here we used a citizen science approach to overcome this obstacle and examined whether the occurrence of Arionidae in Austrian gardens was associated with meteorological (air temperature, precipitation, global solar radiation, relative humidity) or ecological factors (plant diversity, earthworm activity). Occurrence of the invasive A. vulgaris versus the similar-looking native A. rufus was compared using a DNA-barcoding approach.

RESULTS

Slugs were collected from 1061 gardens from the dry Pannonian lowland to the wet alpine climate (altitudinal range 742 m). Slug abundance in gardens was best explained and negatively associated with the parameters "sum of the mean air temperature in spring", "number of frost days in the previous winter" and "mean daily global solar radiation on the day of data collection". Precipitation, plant diversity and earthworm activity were also related to slug abundance, but positively. Out of our genetic sampling of collected slugs, 92% belonged to A. vulgaris.

CONCLUSIONS

Our study showed that citizen science (i) is a feasible approach to record species occurrence in restricted areas across a wide geographical range and (ii) could be more widely employed in order to identify underlying environmental factors of species occurrence.

Mechanisms driving diversity-productivity relationships differ between exotic and native communities and are affected by gastropod herbivory

Biodiversity experiments have shown that productivity usually increases with plant species richness. However, most of those studies disregarded the importance of trophic interactions to the diversity-productivity relationship, and focused on the loss of native species while ignoring invasions by exotic species. Yet, as functional complementarity and the impact of plant antagonists are likely to differ between native and exotic communities, the diversity-productivity relationship may change when native communities are invaded by exotic species. We conducted a mesocosm experiment to test how diversity effects, evenness, and productivity differed between exotic and native assemblages of grassland plants, and how these communities were influenced by slug herbivory. In line with other experiments, we found higher productivity in exotic than in native communities. However, different mechanisms (complementarity vs. selection effect) contributed to the positive diversity-productivity relationships in exotic vs. native communities. Against expectations, native communities showed much lower evenness and a greater selection effect, suggesting that competitive dominance among native species may be even stronger than among exotic species. Slug herbivory decreased productivity independently of species origin and species diversity. However, exotic communities showed a threefold higher complementarity effect than native communities in the absence of slugs, which was mainly driven by differences in the responses of native and exotic legumes and nonleguminous herbs. Our results imply that underlying mechanisms for the positive diversity-productivity relationship differ between native and exotic communities in the early stages of community development, and that differential responses of plant functional groups to generalist herbivory can contribute to this pattern.

Invading slugs (Arion vulgaris) can be vectors for Listeria monocytogenes

AIMS

Listeriosis is a frequent silage-associated disease in ruminants. The slugs Arion vulgaris are invaders in gardens, vegetable crops and meadows for silage production. Field and laboratory studies were conducted to clarify whether slugs could host Listeria monocytogenes and thereby constitute a threat to animal feed safety.

METHODS AND RESULTS

Selective culture of L. monocytogenes from 79 pooled slug samples (710 slugs) resulted in 43% positive, 16% with mean L. monocytogenes values of 405 CFU g(-1) slug tissues. Of 62 individual slugs cultured, 11% also tested positive from surface/mucus. Multilocus sequence typing analysis of 36 isolates from different slug pools identified 20 sequence types belonging to L. monocytogenes lineages I and II. Slugs fed ≅4·0 × 10(5)  CFUL. monocytogenes, excreted viable L. monocytogenes in faeces for up to 22 days. Excretion of L. monocytogenes decreased with time, although there were indications of a short enrichment period during the first 24 h.

CONCLUSIONS

Arion vulgaris may act as a vector for L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Highly slug-contaminated grass silage may pose a potential threat to animal feed safety.

Diversity of enterobacteria including β-lactamase producing isolates associated with the Spanish slug (Arion vulgaris)

The aim of this study was to determine diversity in members of the family Enterobacteriaceae including the beta-lactamase producing isolates associated with the Spanish slug (Arion vulgaris). 81 isolates, each representing a distinct colonial morphotype, were obtained from fecal samples of Spanish slugs and analyzed. Genetically heterogeneous or similar groups were assessed among the isolates by enterobacterial repetitive intergenic consensus (ERIC)-PCR and further characterized by 16S rDNA sequence analysis. Representative strains were allocated to the genera Citrobacter, Raoultella, Escherichia, Klebsiella, Kluyvera, and Buttiauxella. Fifteen isolates, most closely related to Citrobacter freundii and Escherichia coli, displayed an AmpC phenotype, one E. coli isolate showed an ESBL phenotype. These isolates were phenotypically and genotypically characterized by their antimicrobial resistance pattern. Phylogenetic background and multi-locus sequence typing (MLST) of the E. coli isolates were determined. The multi-drug resistant TEM-1 E. coli positive isolate belongs to the phylogenetic group A and ST10. The CMY-2 positive E. coli isolate belongs to the phylogenetic group D and ST117. Our results show that the common garden slug represents an important potential vector of β-lactamase producing Enterobacteriaceae.