Psychrophilic properties and the temperature characteristic of growth of bacteria

Machine learning-assisted discovery of growth decision elements by relating bacterial population dynamics to environmental diversity

Microorganisms growing in their habitat constitute a complex system. How the individual constituents of the environment contribute to microbial growth remains largely unknown. The present study focused on the contribution of environmental constituents to population dynamics via a high-throughput assay and data-driven analysis of a wild-type Escherichia coli strain. A large dataset constituting a total of 12,828 bacterial growth curves with 966 medium combinations, which were composed of 44 pure chemical compounds, was acquired. Machine learning analysis of the big data relating the growth parameters to the medium combinations revealed that the decision-making components for bacterial growth were distinct among various growth phases, e.g., glucose, sulfate, and serine for maximum growth, growth rate, and growth delay, respectively. Further analyses and simulations indicated that branched-chain amino acids functioned as global coordinators for population dynamics, as well as a survival strategy of risk diversification to prevent the bacterial population from undergoing extinction.

Relationship between temperature and growth rate of bacterial cultures

The Arrhenius Law, which was originally proposed to describe the temperature dependence of the specific reaction rate constant in chemical reactions, does not adequately describe the effect of temperature on bacterial growth. Microbiologists have attempted to apply a modified version of this law to bacterial growth by replacing the reaction rate constant by the growth rate constant, but the modified law relationship fits data poorly, as graphs of the logarithm of the growth rate constant against reciprocal absolute temperature result in curves rather than straight lines. Instead, a linear relationship between in square root of growth rate constant (r) and temperature (T), namely, square root = b (T - T0), where b is the regression coefficient and T0 is a hypothetical temperature which is an intrinsic property of the organism, is proposed and found to apply to the growth of a wide range of bacteria. The relationship is also applicable to nucleotide breakdown and to the growth of yeast and molds.

Effects of sudden temperature shifts on pure cultures of four strains of freshwater bacteria

Three psychrotrophic and one mesophilic strains were isolated from winter water samples of different freshwater biotopes and identified asCytophaga johnsonae (C-21),Cytophaga sp. (M-17),Pseudomonas fluorescens (KD), andEnterobacter cloacae (BS-2). Temperature shift-up experiments with emphasis on low temperatures were carried out with aerated pure batch cultures in glucose mineral medium. The effects of sudden temperature increases on growth rates and substrate conversion were investigated. All three psychrotrophic strains in the temperature increase experiments at low temperatures showed differing reactions within the linear zone of the Arrhenius plot. TheC. johnsonae (C-21) shift-up cultures adjusted the growth rate immediately to the rate of the temperature adapted cultures, whereasCytophaga sp. (M-17) shift-up cultures showed a lower andP. fluorescens (KD) a higher growth rate. The mesophilicE. cloacae (BS-2), likeC. johnsonae (C-21), adjusted immediately to the new growth rate. Substrate conversion increased in all experiments immediately after the shift-up. The extracellular substrate conversion byP. fluorescens (KD) of glucose to gluconate and 2-ketogluconate was particularly affected by the sudden temperature increase.

Psychrophilic bacteria

Images