10 - The Role of Heterotrophy in Algae

Abstract

This chapter explores the role of heterotrophy in algae. Benthic algae and phytoplankton have largely been considered strictly photoautotrophic in terms of their energy and carbon requirements. In periphyton assemblages, it has been generally recognized that algae comprise of the autotrophic component, and the heterotrophic members include bacteria, fungi, protists, and other meiofauna. This categorization is not fully accurate, as some bacteria and protists have autotrophic capabilities, and a large number of algae can metabolize heterotrophically. Autotrophy is generally defined as a mode of nutrition whereby solar radiation serves as the source of energy for generating ATP, and inorganic carbon (e.g., CO2 or HCO3) is assimilated by the organism to produce organic carbon, the latter being necessary for the synthesis of cellular components and energy production. In contrast, heterotrophic nutrition does not require light, and utilizes preformed organic compounds from the environment to serve as both an energy source and as a source of carbon-containing building blocks for the organism. Most algae are physiologically equipped to metabolize both autotrophically and heterotrophically. Though autotrophic metabolism is employed most frequently and most efficiently by algae, facultative heterotrophy can be a crucial survival mechanism for light-limited algae.