Mycobacterium gordonae infecting redclaw crayfish Cherax quadricarinatus

Metabarcoding expands knowledge on diversity and ecology of rare actinobacteria in the Brazilian Cerrado

Rare and unknown actinobacteria from unexplored environments have the potential to produce new bioactive molecules. This study aimed to use 16 s rRNA metabarcoding to determine the composition of the actinobacterial community, particularly focusing on rare and undescribed species, in a nature reserve within the Brazilian Cerrado called Sete Cidades National Park. Since this is an inaccessible area without due legal authorization, it is understudied, and, therefore, its diversity and biotechnological potential are not yet fully understood, and it may harbor species with groundbreaking genetic potential. In total, 543 operational taxonomic units (OTUs) across 14 phyla were detected, with Actinobacteria (41.2%), Proteobacteria (26.5%), and Acidobacteria (14.3%) being the most abundant. Within Actinobacteria, 107 OTUs were found, primarily from the families Mycobacteriaceae, Pseudonocardiaceae, and Streptomycetaceae. Mycobacterium and Streptomyces were the predominant genera across all samples. Seventeen rare OTUs with relative abundance < 0.1% were identified, with 82.3% found in only one sample yet 25.5% detected in all units. Notable rare and transient genera included Salinibacterium, Nocardia, Actinomycetospora_01, Saccharopolyspora, Sporichthya, and Nonomuraea. The high diversity and distribution of Actinobacteria OTUs indicate the area's potential for discovering new rare species. Intensified prospection on underexplored environments and characterization of their actinobacterial diversity could lead to the discovery of new species capable of generating innovative natural products.

Threats to UK freshwaters under climate change: Commonly traded aquatic ornamental species and their potential pathogens and parasites

The aquatic ornamental industry, whilst providing socio-economic benefits, is a known introduction pathway for non-native species, which if invasive, can cause direct impacts to native species and ecosystems and also drive disease emergence by extending the geographic range of associated parasites and pathogens and by facilitating host-switching, spillover and spill-back. Although current UK temperatures are typically below those necessary for the survival and establishment of commonly-traded tropical, and some sub-tropical, non-native ornamental species, the higher water temperatures predicted under climate-change scenarios are likely to increase the probability of survival and establishment. Our study aimed primarily to identify which of the commonly-traded non-native ornamental aquatic species (fish and invertebrates), and their pathogens and parasites, are likely to benefit in terms of survival and establishment in UK waters under predicted future climate conditions. Out of 233 ornamental species identified as traded in the UK, 24 were screened, via literature search, for potential parasites and pathogens (PPPs) due to their increased risk of survival and establishment under climate change. We found a total of 155 PPPs, the majority of which were platyhelminths, viruses and bacteria. While many of the identified PPPs were already known to occur in UK waters, PPPs currently absent from UK waters and with zoonotic potential were also identified. Results are discussed in the context of understanding potential impact, in addition to provision of evidence to inform risk assessment and mitigation approaches.

Effects of Nano-Aerators on Microbial Communities and Functions in the Water, Sediment, and Shrimp Intestine in Litopenaeus vannamei Aquaculture Ponds

Nanobubble technology has promising development and application prospects in the fields of sewage treatment, soil and groundwater remediation, animal and plant growth, and biomedicine. However, few studies have investigated its effect on shrimp aquaculture. In this study, we investigated the effect of nano-aerators on microbial communities of the water, sediment, and shrimp gut in a Litopenaeus vannamei aquaculture pond using 16S rRNA high-throughput sequencing. The results indicated that the nano-aerator significantly increased the microbial community diversity and species abundance in the pond, and the microbial community diversity of the pond sediment increased under short-term aeration conditions. Compared to that with ordinary aerators, nano-aerators increased the proportion of beneficial bacteria, such as Exiguobacterium and Acinetobacter, in the water and sediment microbial communities. Moreover, the proportions of beneficial bacteria in the gut, including Rhodobacter, Oscillospira, and Faecalibacterium, were all increased by using the nano-aerator. Therefore, our findings suggest that nano-aerators could promote the activity of beneficial bacteria in aquaculture ecosystems, thereby regulating water quality, reducing disease incidence, and improving aquaculture efficiency and benefits. Our findings provide new insights into the effects of nano-aerators on microbes in crustacean culture ponds.

Genomic structure, expression, and functional characterization of the Fem-1 gene family in the redclaw crayfish, Cherax quadricarinatus

The Fem-1 (Feminization-1) gene, encoding an intracellular protein with conserved ankyrin repeat motifs, has been proven to play a key role in sex differentiation in Caenorhabditis elegans. In the present study, three members of the Fem-1 gene family (designating Fem-1A, Fem-1B, and Fem-1C, respectively) were cloned and characterized in the redclaw crayfish, Cherax quadricarinatus. Sequence analysis showed that all three Fem-1 genes contained the highly conserved ankyrin repeat motifs with variant repeat numbers, which shared similarity with other reported crustaceans. In addition, a phylogenetic tree revealed that the Fem-1 proteins from C. quadricarinatus were clustered with the crustacean Fem-1 homologs, and had the closest evolutionary relationship with Eriocheir sinensis. Quantitative real-time PCR (qRT-PCR) results demonstrated that Fem-1B exhibited a significant higher expression abundance in the ovary than in other tissues. In addition, a regular mRNA expression pattern of the Fem-1B gene appeared in the reproductive cycle of ovarian development. Furthermore, RNA interference experiments were employed to investigate the role of Fem-1B in ovarian development. Moreover, knockdown of Fem-1B by RNAi decreased the expression of VTG in the ovaries and hepatopancreas. In summary, this study pointed out that Fem-1B was involved in the sex differentiation process through regulating VTG expression in C. quadricarinatus, and provided new insights into the role of Fem-1B in ovary development.

An outbreak of crayfish rickettsiosis caused by Coxiella cheraxi in redclaw crayfish (Cherax quadricarinatus) imported to Israel from Australia

The redclaw crayfish (Cherax quadricarinatus) is a freshwater decapod crustacean, cultured in numerous countries worldwide for both food and ornamental purposes. Redclaw crayfish has become an important aquaculture species due to its physical and biological traits, relatively easy breeding, and a short growing-out period to reach commercial size. Bacterial infections are the second-most studied pathogens of freshwater crayfish. However, redclaw crayfish rickettsiosis, caused by Coxiella cheraxi, was reported in only a few scientific papers in the early 2000s, in Australia and Ecuador. Coxiella cheraxi is a rod-shaped intracellular bacterium that can cause mortality of 22%-80% in naturally infected crayfish. In experimental infections, mortality rates may be even higher (40%-90%). Coxiella cheraxi is closely related to Coxiella burnetii, the agent of Q-fever, which affects ruminants (goats, sheep, and cattle) and occasionally may cause zoonotic infections. According to the scientific knowledge available, C. cheraxi is a species-specific pathogen because it has been only detected in Cherax quadricarinatus and thus far, there is no evidence of a zoonotic potential. In this study, we describe an outbreak of rickettsiosis in a batch of redclaw crayfish imported to Israel from an Australian hatchery, observed 2 months after introduction in a quarantine facility. Initial mortality was evaluated through histopathology, revealing infection by rickettsia-like organisms (RLO) that were subsequently investigated by molecular analysis and transmission electron microscopy examination. Phylogenetic analysis revealed that the detected RLO were closely related to C. cheraxi from a single source (Australian strain TO98), available in free publicly accessible databases. After 5 months in quarantine, almost 99% of the crayfish population had died. Our findings raise valuable questions related to aquatic animal trade and the importance of mitigation measures, such as quarantine and routine diagnostic procedures, to limit the spread of infectious diseases.

Etiological characteristics of "tail blister disease" of Australian redclaw crayfish (Cherax quadricarinatus)

In November 2019, an acute disease outbreak in Australian redclaw crayfish (Cherax quadricarinatus) occurred in a farm in Hubei, China, with a cumulative mortality rate of over 80%. One of the characteristic symptoms of the disease was blisters on the tail. This symptom is also common in diseased Procambarus clarkii every year in this country, but the causative agent has not been determined. This study analyzed the etiological characteristics of this disease. Bacterial isolation and identification combined with high-throughput sequencing analysis were conducted to obtain the microbiota characteristics in the hemolymph, hepatopancreas, and intestines. Results showed that this outbreak was caused by infection from Aeromonas hydrophila and Aeromonas veronii. The underlying cause was stress imposed on crayfish during transferring from outdoor pond to indoor pond because of temperature drops. Aeromonas infection caused remarkable changes in the structure of the microbial composition in the hemolymph, hepatopancreas, and intestines of the crayfish. The abundance of Aeromonas in the hemolymph of the sick crayfish was as high as 99.33%. In particular, KEGG metabolic pathway analysis showed that some antibiotic synthesis, enterobactin biosynthesis, and myo-inositol degradation pathways were abundant in healthy crayfish hemolymphs, which may be the mechanism of maintaining crayfish health. Conversely, inhibition of these pathways led to the disorder of microbiota structure, finally leading to the occurrence of diseases. To the knowledge of the authors, this study was the first to use high-throughput amplicon sequencing targeting the 16S rRNA gene to find the causative bacteria in aquatic animals. This protocol can provide more comprehensive and reliable evidence for pathogen identification, even if the pathogenic bacteria are anaerobes or other hard-to-culture bacteria.

Microbial pathogens of freshwater crayfish: A critical review and systematization of the existing data with directions for future research

Despite important ecological role and growing commercial value of freshwater crayfish, their diseases are underresearched and many studies examining potential crayfish pathogens do not thoroughly address their epizootiology, pathology or biology. This study reviews over 100 publications on potentially pathogenic viruses, bacteria, fungi and fungal-like microorganisms reported in crayfish and systematizes them based on whether pathogenicity has been observed in an analysed species. Conclusions on pathogenicity were based on successful execution of infectivity trials. For 40.6% of examined studies, microbes were successfully systematized, while for more than a half (59.4%) no conclusion on pathogenicity could be made. Fungi and fungal-like microorganisms were the most studied group of microbes with the highest number of analysed hosts, followed by bacteria and viruses. Our analysis demonstrated the need for: (a) inclusion of higher number of potential host species in the case of viruses, (b) research of bacterial effects in tissues other than haemolymph, and (c) more research into potential fungal and fungal-like pathogens other than Aphanomyces astaci. We highlight the encountered methodological challenges and biases and call for a broad but standardized framework for execution of infectivity trials that would enable systematic data acquisition on interactions between microbes and the host.

Mycobacteriosis in Aquatic Invertebrates: A Review of Its Emergence

Mycobacteriosis is a chronic bacterial disease reported in aquatic and terrestrial animals, including humans. The disease affects a wide range of cultured and wild organisms worldwide. Mycobacteriosis is well-known in aquatic vertebrates (e.g., finfish, marine mammals), while in the last few years, reports of its presence in aquatic invertebrates have been on the rise, for both freshwater and marine species. The number of cases is likely to increase as a result of increased awareness, surveillance and availability of diagnostic methods. Domestication of wild aquatic species and the intensification of modern aquaculture are also leading to an increase in the number of reported cases. Moreover, climate changes are affecting fresh and marine aquatic ecosystems. The increasing reports of mycobacteriosis in aquatic invertebrates may also be influenced by global climate warming, which could contribute to the microbes' development and survival rates, pathogen transmission and host susceptibility. Several species of the genus Mycobacterium have been diagnosed in aquatic invertebrates; a few of them are significant due to their wide host spectrum, economic impact in aquaculture, and zoonotic potential. The impact of mycobacteriosis in aquatic invertebrates is probably underestimated, and there is currently no effective treatment other than facility disinfection. In this review, we provide an overview of the diversity of mycobacterial infections reported in molluscs, crustaceans, cnidarians, echinoderms and sponges. We highlight important issues relating to its pathological manifestation, diagnosis and zoonotic considerations.