Mine Aric H, Coleman Maureen L, Colman Albert S
Department of Earth and Environmental Sciences, California State University, Fresno, CA, United States.
Department of the Geophysical Sciences, University of Chicago, Chicago, IL, United States.
Front Microbiol. 2021 Apr 8;12:641700. doi: 10.3389/fmicb.2021.641700. eCollection 2021.
The availability of phosphorus limits primary production in large regions of the oceans, and marine microbes use a variety of strategies to overcome this limitation. One strategy is the production of alkaline phosphatase (APase), which allows hydrolysis of larger dissolved organic phosphorus (DOP) compounds in the periplasm or at the cell surface for transport of orthophosphate into the cell. Cell lysis, driven by grazing and viral infection, releases phosphorus-containing cell components, along with active enzymes that could persist after lysis. The importance of this continued enzymatic activity for orthophosphate regeneration is unknown. We used three model bacteria - K-12 MG1655, sp. WH7803, and sp. MED4 - to assess the impact of continued APase activity after cell lysis, via lysozyme treatment, on orthophosphate regeneration. Direct release of orthophosphate scaled with cell size and was reduced under phosphate-starved conditions where APase activity continued for days after lysis. All lysate incubations showed post-lysis orthophosphate generation suggesting phosphatases other than APase maintain activity. Rates of DOP hydrolysis and orthophosphate remineralization varied post-lysis among strains. K-12 MG1655 rates of remineralization were 0.6 and 1.2 amol cellhr under deplete and replete conditions; WH7803 lysates ranged from 0.04 up to 0.3 amol cellhr during phosphorus deplete and replete conditions, respectively, while in MED4 lysates, rates were stable at 0.001 amol cellhr in both conditions. The range of rates of hydrolysis and regeneration underscores the taxonomic and biochemical variability in the process of nutrient regeneration and further highlights the complexity of quantitatively resolving the major fluxes within the microbial loop.
磷的可利用性限制了海洋大片区域的初级生产，海洋微生物采用多种策略来克服这一限制。一种策略是产生碱性磷酸酶（APase），它能使周质或细胞表面较大的溶解有机磷（DOP）化合物水解，以便将正磷酸盐转运到细胞内。由捕食和病毒感染驱动的细胞裂解会释放含磷的细胞成分，以及裂解后仍能持续存在的活性酶。这种持续的酶活性对正磷酸盐再生的重要性尚不清楚。我们使用了三种模式细菌——K-12 MG1655、WH7803菌和MED4菌，通过溶菌酶处理来评估细胞裂解后APase活性的持续存在对正磷酸盐再生的影响。正磷酸盐的直接释放与细胞大小成比例，并且在磷酸盐饥饿条件下会减少，在这种条件下，APase活性在裂解后会持续数天。所有裂解物孵育都显示出裂解后正磷酸盐的生成，这表明除APase外的磷酸酶仍保持活性。裂解后不同菌株的DOP水解速率和正磷酸盐再矿化速率各不相同。在耗尽和充足条件下，K-12 MG1655的再矿化速率分别为0.6和1.2 amol/细胞·小时；WH7803裂解物在磷耗尽和充足条件下分别为0.04至0.3 amol/细胞·小时，而在MED4裂解物中，两种条件下的速率均稳定在0.001 amol/细胞·小时。水解和再生速率的范围突出了营养物再生过程中的分类学和生化变异性，并进一步凸显了定量解析微生物环内主要通量的复杂性。
