Collaborative Research: Activity and abundance of photoheterotrophs fueled by photochemically-produced substrates

合作研究：光化学产生的底物驱动的光异养生物的活性和丰度

• 批准号: 1029569
• 负责人: David Kieber
• 金额: $ 38.95万
• 依托单位: SUNY College of Environmental Science and Forestry
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1029569&HistoricalAwards=false
• 关键词: Collaborative; Research; Activity; abundance; photoheterotrophs

Intellectual Merit: Bacteria that use both dissolved organic material (DOM) and light, i.e. photoheterotrophs, would fundamentally change views of how energy and material are processed in the oceans. However, it is still not clear if these microbes have unique roles in the oceans because standard experiments have not been successful in consistently demonstrating positive effects of light on growth and respiration of presumed photoheterotrophs. It is known that these microbes are abundant, with one type (those containing proteorhodopsin) alone constituting 50% or more of all microbes in the oceans. But why these microbes are so abundant is unknown as the ecological advantages of photoheterotrophy remain obscure.The PIs will use a new approach and novel experiments to examine how light affects photoheterotrophs and to explore the contribution of these microbes to DOM fluxes. Their work is testing the following hypothesis: The biogeochemical role of photoheterotrophs is to use low energy-yielding DOM components such as products of photochemical reactions. The reactions involve chromophoric DOM (CDOM) which is a large and dynamic part of the carbon cycle especially in coastal oceans. They have hypothesized that the light energy gained by photoheterotrophs would enable these microbes to benefit from using photochemically-produced compounds which alone do not yield much energy. This hypothesis is supported by lab experiments showing that proteorhodopsin-generated energy becomes important only when respiration is inhibited and cells are limited by energy. Other lab experiments demonstrated that anaplerotic fixation of CO2 by PR-containing bacteria is stimulated by light. This fixation is needed for growth on C1-C4 compounds, including many produced by photochemical reactions.The PIs are testing this hypothesis with experiments in the Delaware estuary where CDOM varies greatly spatially and seasonally. They are examining the effect of light (PAR) on the uptake and respiration of photochemically-produced low molecular weight (LMW) organic compounds and on gene expression (mRNA) of photoheterotrophs. The focus is on CO, pyruvate, acetaldehyde, and glyoxal; together these compounds constitute a large fraction of the photochemical-byproducts in seawater. Glycolate is also being examined because of its importance in phytoplankton excretion and because of its similarity to organic acids produced by photochemical reactions. Uptake of these compounds is estimated with 14C- tracers and HPLC measurements of concentrations. Rates are then compared with the abundance and mRNA levels of proteorhodopsin and pufM found in aerobic anoxygenic phototrophic bacteria as measured by QPCR assays. The PIs are also examining how light and the photochemically-produced LMW organic compounds affect bacterial respiration and growth efficiency. They are examining the relationships among anaplerotic CO2 fixation, uptake of photochemical byproducts, and photoheterotroph abundance and activity along transects of the Delaware estuary and during diel studies.The proposed work is being conducted by a team consisting of microbial oceanographers (Kirchman and Cottrell) and a marine biogeochemist (Kieber) with expertise in photoheterotrophs and photochemical reactions, respectively.Broader Impacts: This interdisciplinary project is supporting graduate students and also involves undergraduates in summer research projects. Results will be incorporated into web sites and used in courses taught by Kirchman and Kieber. The Kirchman lab is featured in lab tours open to the public and in Coast Day, an annual open house that attracts about 10,000 visitors. Kieber mentors undergraduates and coordinated a program for economically disadvantaged high school students.

智力优点：同时利用溶解有机物质（DOM）和光的细菌（即光异养生物）将从根本上改变人们对海洋中能量和物质处理方式的看法。然而，目前尚不清楚这些微生物在海洋中是否具有独特的作用，因为标准实验未能成功地一致证明光对假定的光异养生物的生长和呼吸的积极影响。众所周知，这些微生物非常丰富，仅其中一种（含有变形视紫红质的微生物）就占海洋中所有微生物的 50% 或更多。但为什么这些微生物如此丰富尚不清楚，因为光异养生物的生态优势仍然不清楚。PI 将使用一种新方法和新颖的实验来研究光如何影响光异养生物，并探索这些微生物对 DOM 通量的贡献。他们的工作正在测试以下假设：光异养生物的生物地球化学作用是利用低能量产的 DOM 成分，例如光化学反应的产物。这些反应涉及发色 DOM (CDOM)，它是碳循环的一个重要且动态的部分，尤其是在沿海海洋中。他们假设，光异养生物获得的光能将使这些微生物受益于使用光化学产生的化合物，而光化学产生的化合物本身并不能产生太多能量。这一假设得到了实验室实验的支持，实验表明，只有当呼吸受到抑制并且细胞受到能量限制时，蛋白视紫红质产生的能量才变得重要。其他实验室实验表明，光会刺激含 PR 的细菌对 CO2 的回补固定。这种固定对于 C1-C4 化合物（包括许多由光化学反应产生的化合物）的生长是必需的。PI 正在特拉华州河口进行实验来检验这一假设，那里的 CDOM 在空间和季节上变化很大。他们正在研究光（PAR）对光化学产生的低分子量（LMW）有机化合物的吸收和呼吸以及光合异养生物的基因表达（mRNA）的影响。重点是二氧化碳、丙酮酸盐、乙醛和乙二醛；这些化合物共同构成了海水中光化学副产物的很大一部分。由于其在浮游植物排泄中的重要性以及与光化学反应产生的有机酸的相似性，乙醇酸盐也受到了研究。通过 14C-示踪剂和 HPLC 浓度测量来估计这些化合物的吸收。然后将比率与通过 QPCR 测定测量的需氧无氧光养细菌中发现的蛋白视紫红质和 pufM 的丰度和 mRNA 水平进行比较。 PI 还在研究光和光化学产生的 LMW 有机化合物如何影响细菌呼吸和生长效率。他们正在研究回补二氧化碳固定、光化学副产物的吸收以及特拉华河口横断面和昼夜研究期间的光合异养生物丰度和活性之间的关系。这项拟议的工作是由微生物海洋学家（Kirchman 和 Cottrell）和一位在光合异养生物和光合生物地球化学家（Kieber）组成的团队进行的。 更广泛的影响：这个跨学科项目为研究生提供支持，也让本科生参与夏季研究项目。结果将被纳入网站并用于基希曼和基伯教授的课程。基希曼实验室在向公众开放的实验室参观活动以及每年吸引约 10,000 名参观者的海岸日开放日中得到展示。基伯指导本科生并协调针对经济困难高中生的计划。