Azotobacter Cysts

Abstract

Azotobacter is a genus of Gram‐negative, organotrophic, nitrogen‐fixing soil bacteria. These bacteria undergo a differentiation process to form cysts, which are dormant cells resistant to deleterious conditions. A cyst consists of a contracted oval cell, called central body, covered with a two‐layer capsule. Although the process of encystment has been known for many years and many physiological and morphological studies were published decades ago, the biosynthetic pathways of the major components of the cyst and how they are regulated remained largely unknown. More recent work has elucidated the biosynthesis and genetics of some of these components, like alginate, polyhydroxybutyrate and the phenolic lipids alkylresorcinols and alkylpyrones and also the regulators controlling their biosynthesis and the changes occurring during encystment, such as the loss of flagella. Among these regulators are the alternative sigma factors AlgU and RpoS, the global regulatory systems Gac/Rsm and the transcriptional regulators AlgR, ArpR and CydR. Key Concepts: The encysting process results in a dormant cell more resistant to adverse conditions than the vegetative cell. During the encysting process, a coordinated array of metabolic and morphological changes take place to produce a dormant cell. The central body of the cyst is surrounded by a protective two‐layered capsule, which is composed of carbohydrates, proteins and lipids. The exopolysaccharide alginate constitutes a structural part of the cyst envelope and is essential for desiccation resistance. Several regulators of gene expression control the differentiation process, leading to production of cyst.

Glucose uptake in Azotobacter vinelandii occurs through a GluP transporter that is under the control of the CbrA/CbrB and Hfq-Crc systems

“…Although A . vinelandii is phylogenetically related to Pseudomonas species, it possesses distinctive features that clearly separates it from the genus Pseudomonas , such as its capacity to differentiate and form dormant cysts that are resistant to drought, its strict aerobic metabolism and its capacity to fix nitrogen under aerobic conditions 2, 3 . A .…”

The Regulatory Hierarchy Following Signal Integration by the CbrAB Two-Component System: Diversity of Responses and Functions

“…During this transition, GacSA intervenes through the Rsm proteins in the switching between type-3 and type-6 secretion system (T3SS, T6SS) [ 160 ], biofilm formation, polysaccharide synthesis, iron uptake [ 161 ] as well as synthesis of quorum-sensing signals [ 158 , 162 , 163 ]. Moreover, in A. vinelandii , it participates in the synthesis of alkylresorcinols that are related to the encystment process [ 164 ], two polymers of biotechnological interest, poly-β-hydroxybutyrate and alginate [ 165 , 166 ], and also activates motility and flagella synthesis [ 167 ].…”

A Methodology for Identifying Phenomenological‐Based Models using a Parameter Hierarchy

“…PHAs possess similar qualities to the plastics produced from petrochemical derivatives such as hard plastics, brittle plastics or even rubber. Due to their biological nature and their production from renewable resources, PHAs have been the object of numerous studies in the last years . There are two prevalent methods for the production of PHAs depending on the microorganism used.…”