The role of PTP-like phytases in ruminal phytate digestion

植酸盐是储存在谷物中的磷的主要形式，因此也是集约化畜牧业生产中以谷物为基础的日粮中磷的主要来源。植酸-磷对非反刍动物(如猪、家禽)是不能消化的，并从粪便中排出。在耕地上施用粪肥后，植酸磷的释放是一个重要的污染源，并导致世界上非反刍动物密度高的地区的地表水富营养化。全球非反刍动物每年排出的磷超过8亿公斤，给生产者带来了每年超过10亿美元的损失。解决非反刍动物无法使用日粮植酸盐的一种方法是用植酸酶修改日粮。植酸酶释放植酸-磷，从而使非反刍动物可以利用植酸-磷。有趣的是，瘤胃中的微生物活动使反刍动物(如牛、羊)能够利用植酸-磷。我研究的总体目标是确定瘤胃厌氧细菌如何降解植酸盐。我们已经在瘤胃中鉴定出一些高产植酸酶的厌氧菌，包括第IX簇中的Selenomonads及其近亲。我建议利用生物化学和分子生物学的技术来研究单胞菌及其相关厌氧细菌降解植酸的遗传学和生化。我的研究小组最近描述了由这些瘤胃细菌产生的一个新的植酸酶家族。我们已经鉴定了6种与蛋白酪氨酸磷酸酶有远缘关系的酶，蛋白酪氨酸磷酸酶是一类重要的参与调节基本细胞过程的酶。我们目前正在确定这一新的植酸酶家族的结构、作用模式和分布，试图深入了解植酸降解及其在瘤胃磷循环中的作用。这项研究将为有效应对日益严重的污染问题提供新的解决方案和工具。

Phytate is the principal form of phosphorus stored in grains and, as such is the major source of phosphorus in grain-based diets used in intensive livestock production. Phytate-phosphorus is indigestible to non-ruminant livestock (e.g., swine, poultry) and excreted in the feces. Release of phytate-phosphorus following application of manure to arable lands is a significant source of pollution and has contributed to eutrophication of surface waters in areas of the world with high densities of non-ruminant livestock. The annual amount of phosphorus excreted globally by non-ruminants exceeds 800,000,000 kg and represents to producers an annual worldwide loss of greater than $1 billion dollars. One solution to the inability of non-ruminants to use dietary phytate is the amendment of diets with phytases. Phytases release phytate-phosphorus, thereby making it available to non-ruminant animals. Interestingly, microbial activities in the rumen enable ruminant animals (e.g., cattle, sheep) to use phytate-phosphorus. The overall objective of my research is to determine how ruminal anaerobic bacteria degrade phytate. We have identified a number of high phytase producing anaerobic bacteria in the rumen, including Selenomonads and relatives in cluster IX. I propose to use techniques in biochemistry and molecular biology to study the genetics and biochemistry of phytate degradation by Selenomonads and related anaerobic bacteria. My research group has recently described a novel family of phytases produced by these rumen bacteria. We have characterized 6 enzymes that are distantly related to Protein Tyrosine Phosphatases, an important class of enzymes involved in regulating fundamental cellular processes. We are currently determining the structure, mode of action and distribution of this new family of phytase in an attempt to gain insights into phytate degradation and its role in phosphorus cycling in the rumen. This research will provide new solutions and tools to deal effectively with a growing pollution problem.