Ultrastructure of a spirochete found in tissues of the brine shrimp, Artemia salina

MSBOTS: a multiple small biological organism tracking system robust against non-ideal detection and segmentation conditions

Accurately tracking a group of small biological organisms using algorithms to obtain their movement trajectories is essential to biomedical and pharmaceutical research. However, object mis-detection, segmentation errors and overlapped individual trajectories are particularly common issues that restrict the development of automatic multiple small organism tracking research. Extending on previous work, this paper presents an accurate and generalised Multiple Small Biological Organism Tracking System (MSBOTS), whose general feasibility is tested on three types of organisms. Evaluated on zebrafish, Artemia and Daphnia video datasets with a wide variety of imaging conditions, the proposed system exhibited decreased overall Multiple Object Tracking Precision (MOTP) errors of up to 77.59%. Moreover, MSBOTS obtained more reliable tracking trajectories with a decreased standard deviation of up to 47.68 pixels compared with the state-of-the-art idTracker system. This paper also presents a behaviour analysis module to study the locomotive characteristics of individual organisms from the obtained tracking trajectories. The developed MSBOTS with the locomotive analysis module and the tested video datasets are made freely available online for public research use.

Selected bacterial strains protect Artemia spp. from the pathogenic effects of Vibrio proteolyticus CW8T2

In this study Vibrio proteolyticus CW8T2 has been identified as a virulent pathogen for Artemia spp. Its infection route has been visualized with transmission electron microscopy. The pathogen affected microvilli and gut epithelial cells, disrupted epithelial cell junctions, and reached the body cavity, where it devastated cells and tissues. In vivo antagonism tests showed that preemptive colonization of the culture water with nine selected bacterial strains protected Artemia juveniles against the pathogenic effects. Two categories of the selected strains could be distinguished: (i) strains providing total protection, as no mortality occurred 2 days after the experimental infection with V. proteolyticus CW8T2, with strain LVS8 as a representative, and (ii) strains providing partial protection, as significant but not total mortality was observed, with strain LVS2 as a representative. The growth of V. proteolyticus CW8T2 in the culture medium was slowed down in the presence of strains LVS2 and LVS8, but growth suppression was distinctly higher with LVS8 than with LVS2. It was striking that the strains that gave only partial protection against the pathogen in the in vivo antagonism test showed also a restricted capability to colonize the Artemia compared to the strains providing total protection. The in vivo antagonism tests and the filtrate experiments showed that probably no extracellular bacterial compounds were involved in the protective action but that the living cells were required to protect Artemia against V. proteolyticus CW8T2.

Bacterial symbionts on green hydra and their effect on phosphate uptake

Gram-negative rod-shaped bacteria (1.5-2μm long and 0.5μm wide) have been found associated with green hydra. They are always present on the hydra surface delineating the ectodermal cells, on animals in culture, and also on those sampled from a natural habitat. The bacteria could be removed by a 30-min treatment with antibiotics (50μ/ml polymyxin B and 50μ/ml streptomycin). Antibiotic-treated hydra took up 55% less phosphate from the medium than control hydra. The nutritional relationship between the bacteria and green hydra and possible routes of infection of the hydra by these prokaryotic symbionts are discussed. Their importance in interpreting results of certain types of physiological experiments using aquatic organisms is emphasized.

Tubular structures associated with intracytoplasmic spirochetes

When tissues of spirochete-infected brine shrimp (Artemia salina) were examined by electron microscopy, tubular structures were often seen closely associated with intracytoplasmic spirochete profiles. These tubules were never observed in association with spirochetes found in the haemocoeal or other extracellular spaces. Since the trilaminar layer comprising the wall of the tubules was identical in ultrastructure to the outer envelope of the spirochete, these structures were interpreted to be finger-like extensions of the spirochete outer envelope.