CCMAR/University of Algarve, Faro, Portugal.
Arch Environ Contam Toxicol. 2010 Oct;59(3):433-43. doi: 10.1007/s00244-010-9490-9. Epub 2010 Mar 16.
A series of artificial microcosms was used to test the effect of clam density on benthic iron biogeochemistry and, subsequently, if the response of clam Ruditapes decussatus to infection with Perkinsus olseni, a common opportunistic parasite known to be iron dependent, was correlated with the dynamics of iron sediment pore waters within the chambers. Three series of benthic microcosms were used in the experiment, comparing similar densities of clams (none, one, two, three, or four individuals/chamber) between a control set (no deliberate infection) and two parallel sets of clams that were deliberately infected with the parasite after 10 days of incubation. Fifteen chambers were used simultaneously and the experiment was conducted for 35 days. In order to avoid spurious effects of differential organic loading and clam feeding efficiency on the oxidative state of the sediment, the iron balance was tentatively shifted during incubation toward decreased dissolved iron in pore water. This was done by applying a constant flow of air to all chambers and refraining from supplying extra organic matter during the experimental run, which led to the reduction of benthic oxygen demand as the experiment progressed. Results showed that microcosms bearing both higher clam densities and lower infection levels were able to exert a quantitative influence in iron biogeochemistry through bioturbation activity. This effect was significantly depressed in chambers hosting clams with high infection levels. In addition, analysis of molecular markers responsive to iron and parasite stress revealed an upper regulation of HSP70 and ferritin in infected clams, thus suggesting a role of those molecules on both host protection and response to parasite presence by limiting iron availability. Together, these findings suggest a correlation between the expression of clam molecular iron/stress markers and iron bioavailability, which can be modified by the presence or absence of Perkinsus infection. In turn, we propose that clam lethargy in response to parasite invasion might help to combat infection by reducing iron mobilization in the surrounding sediment through a decrease in bioturbation activity, thus reducing its availability to the parasite.
使用一系列人工微宇宙来测试蛤密度对底栖铁生物地球化学的影响，随后，如果蛤（Ruditapes decussatus）对寄生虫（一种常见的机会性寄生虫，已知其铁依赖性）感染的反应与腔室内铁沉积物孔隙水的动态相关，那么这种反应是否与腔室内铁沉积物孔隙水的动态相关。实验中使用了三组底栖微宇宙，在对照组（无故意感染）和两组平行组的蛤中比较了类似密度的蛤（无、一个、两个、三个或四个个体/腔室），这两组平行组的蛤在孵育 10 天后被故意感染寄生虫。同时使用了 15 个腔室，实验进行了 35 天。为了避免有机负荷和蛤摄食效率的差异对沉积物氧化状态产生虚假影响，在孵育过程中暂时将铁平衡向孔隙水中溶解铁减少的方向转移。这是通过向所有腔室持续供应空气并在实验过程中不提供额外的有机物来实现的，这导致随着实验的进行，底栖需氧量减少。结果表明，通过生物扰动活动，承载较高蛤密度和较低感染水平的微宇宙能够对铁生物地球化学产生定量影响。在承载高感染水平蛤的腔室中，这种作用显著受到抑制。此外，对响应铁和寄生虫应激的分子标记物的分析表明，感染蛤中的 HSP70 和铁蛋白受到上调，因此表明这些分子在宿主保护和对寄生虫存在的反应中发挥作用，通过限制铁的可用性来实现。总之，这些发现表明蛤分子铁/应激标记物的表达与铁生物可利用性之间存在相关性，这种相关性可以通过 Perkinsus 感染的存在与否来改变。反过来，我们提出，蛤对寄生虫入侵的反应迟钝可能有助于通过减少生物扰动活动来减少周围沉积物中铁的动员，从而减少寄生虫对铁的可用性，从而抵抗感染。
