Growth of Rhizobium japonicum Strains at Temperatures Above 27°C

Abstract

A study was conducted to examine the growth responses of different Rhizobium japonicum strains to increasing temperatures, determine the degree of variability among strains in those responses, and identify temperature-related growth characteristics that could be used to select temperature-tolerant strains. Each of 42 strains was grown in liquid culture for 96 h at 19 incubation temperatures ranging from 27.4 to 54.1°C in a temperature gradient apparatus. Growth was estimated by measuring the change in optical density over time. Strains differed in their responses to increasing temperatures. Three characteristic temperatures were determined for each strain: the temperature giving the maximum optical density at 96 h (optimum temperature), the maximum temperature allowing a continuous increase in optical density during the 96-h period (maximum permissive temperature), and the maximum temperature allowing growth of the cultures after they were transferred to a uniform incubation temperature of 28°C (maximum survival temperature). The three characteristic temperatures varied among strains and had the following ranges: optimum temperature, from 27.4 to 35.2°C; maximum permissive temperature, from 29.8 to 38.0°C; and maximum survival temperature, from 33.7 to 48.7°C. Significant positive correlations were found between maximum permissive temperature and optimum temperature and between maximum permissive temperature and maximum survival temperature. Eight strains which had the highest maximum permissive temperature, optimum temperature, and maximum survival temperature were considered tolerant of high temperatures and were able to grow at temperatures higher than those previously reported for the most tolerant R. japonicum strains. The strains were of diverse geographical origin, but the response to high temperatures was not related to their origin. Evaluation of the temperature responses in pure culture may be useful in the search for R. japonicum strains better suited to environments in which high soil temperature is a limiting factor.

Most heat-tolerant rhizobia show high induction of major chaperone genes upon stress

“…Taking into account several studies showing that strains' endurance to high temperatures in a culture medium correlates with their symbiotic performance under heat stress (Munevar & Wollum, 1981b; Rahmani et al ., 2009), the thermotolerant chickpea rhizobia identified in the present work could have potential agronomical importance. For example, isolate PMI‐1‐Portimão has a high symbiotic effectiveness (>75%) and is among the isolates with higher tolerance to all the tested conditions; hence, it represents a good candidate for field inoculation.…”

“…The optimum temperature range for most rhizobia is 25–31 °C (Somasegaran & Hoben, 1994) and the upper temperature limits are between 32 and 47 °C (Munevar & Wollum, 1981a; Karanja & Wood, 1988). However, these limits vary among species and strains.…”

Relationship of the Presence and Copy Number of Plasmids to Exopolysaccharide Production and Symbiotic Effectiveness in Rhizobium fredii USDA 206

“…EPS analysis. Culture supernatants from YEM-grown, stationary-phase cells were concentrated by lyophilization (30). The optimum growth temperature was the temperature at which the highest growth rate (as measured by a change in the optical density) was obtained.…”

Preservation of Rhizobium viability and symbiotic infectivity by suspension in water

“…Temperature affected the viability of water-stored rhizobia in generally the same manner as found for rhizobia stored in other ways. Earlier studies showed that most R. japonicum strains do not survive temperatures of 40°C either in peatbased inocula (5) or in liquid culture (20).…”