Research
Obligatory blood feeder arthropods like ticks rely on endosymbiotic bacteria to supplement their diet with B-vitamins not found in blood. Other metabolites, as l-proline, were suggested to be involved in this nutritional symbiosis but were not tested. Here we studied the metabolite-based interaction in the brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae) and its Coxiella like endosymbionts (CLE) system. We measured amino acid titers and tested the effect of B-vitamins and l-proline supplementation on the fitness of CLE deprived (low titers of CLE) female ticks. We found higher titers of l-proline in symbiont hosting organs of unfed ticks, and in engorged (blood fed) whole ticks. Supplementation of B-vitamins increased the hatching rate of ticks deprived of CLE, and this effect seems stronger when l-proline was also added. Our results indicate that l-proline is produced by CLE, and suggest that CLE are essential under high metabolic demand such as oogenesis and embryonic development, which further affect tick reproductive fitness. These findings demonstrate the broader effect nutritional symbionts have on their host and can serve as a potential target for controlling ticks and tick-borne diseases.
Maternally transmitted obligatory endosymbionts, found in female gonads and somatic tissues, are expected to supply missing metabolites to their hosts. These deficiencies are presumably addressed by specific symbiotic microorganisms, such as Coxiella-like endosymbionts (CLEs) of Rhipicephalus ticks. CLEs localize in specialized host tissue cells within the Malpighian tubules (Mt) and the ovaries (Ov), from which they are maternally transmitted to developing oocytes. The differing functions and cell types of these two organs suggest varied roles for CLEs, which remain unknown. To investigate CLE functions, a comparative proteomics study was conducted between Mt and Ov of R. sanguineus ticks. This study identified several CLE proteins that were more abundant in each organ. Gene Ontology analysis indicated that most proteins enriched in Mt are related to cellular metabolic functions and stress responses, while those in Ov are predominantly linked to cell proliferation. This suggests tat CLEs function differentially and interdependently with host requirements specific to each organ. Our findings propose that Mt CLEs provide essential nutrients to the host, while Ov CLEs promote proliferation and vertical transmission to tick progeny. The different functional specificity of CLEs in these organs implies that their metabolic capabilities evolved according to the constraints imposed by specific organ functions and requirements. These insights offer targeted CLE proteins for future studies focusing on CLE biology and tick population control.
Acquired tick resistance (ATR) occurs when ticks can no longer feed on host and prevents pathogen transmission. Tick vaccines offers a promising solution to ATR, but their efficacy is limited to specific tick species. Here we tested the effectiveness of 19ISP mRNA LNPs, Ixodes scapularis salivary proteins against the feeding behavior of Amblyomma americanum ticks. We immunized guinea pigs with 19ISP mRNA LNPs and for control we used luciferase and they were exposed to A. americanum ticks. The vaccinated guinea pigs did not developed erythema, which is the first sign of ATR. However, we observed delay in feeding and found marginal discrepancies in the cohorts of tick engorgement weight. During temporal analysis, we also found that alpha gal expression is higher during 48 h and 72 h of feeding than at other time points in salivary glands of A. americanum ticks. Slower than anticipated, rather than tick rejection, we found delay in feeding. Based on our preliminary insights we aim to leverage this knowledge in vaccine development by salivary proteins that are common between these tick species might serve as a vaccine antigen targets.