Growth phases and kinetic equations of Lysinubacillus sphaericus under different culture conditions and its importance for biocementation.

MANRRIQUE HUGHES, IVÁN JEREMÍAS; MALDONADO TORALES, MANUELA; MARZARI, MARÍA JOSEFINA; GUILARDUCCI, ANABELA; CRESPO, KARINA; PARAJE, MARÍA GABRIELA

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General.; 2023

Biocementation is an innovative and eco-friendly technique used for crack repair basedon the microbial-induced carbonate precipitation (MICP). The results are the biogenic ofcalcium carbonate (CaCO3) as well as forming bridges that can fill cracks, bond loosematerials, and strengthen surfaces that result in biocementation of fragmented andexfoliated surfaces. The development and application of mathematical models, particularlykinetic models, can play a significant role in predicting product formation and providingstrategies for solving various challenges encountered in biocementation processes.The objective of this work was to study the growth curve phases and mathematicalkinetics equations of Lysinibacillus sphaericus under different culture conditions todetermine the optimal nutrient concentrations, temperature, and pH were registered.Growth curves were performed in a semi-logarithmic plot of Optical Density versus Time(6, 12, 24, 48 hours) at two temperatures (24 and 37 °C) in Tryptic Soy Broth (TSB) andLuria-Bertani (LB) medium. The change in pH was recorded using a pH meter. Finally, usingmathematical equations we calculated the number of generations (n= (log(N final)-log(Ninitial))/log(2)), the generation time (τ= Time Elapsed/Number of Generations), and thespecific growth rate (µ = 0.693/Generation Time).In both culture mediums, a similar profile in the growth curve was observed with threephases, Lag, Exponential, and Stationary, and better results were found in LB at 37 ºC. Forbiocementation, this culture medium is the best alternative due to its composition beingcompatible with concrete standards. The number of generations (n) represents how manytimes a microbial population doubles during a given time period, and was n=1 for TSB at37°C, n=3 for TSB at 24°C, n=1 for LB at 37°C and n=2 for LB at 24°C. Generation time (τ)is an important parameter that characterizes the rate of growth and for TSB at 37°C was254 min and 925 min at 24°C. Besides, for LB at 37 °C and 24°C was 219 and 1000 min,respectively. The specific growth rate (µ) represents the rate at which a microbial populationgrows per unit of time and it's a key parameter for understanding the growth dynamics of amicrobial culture. We found that µ was 0.0027 min-1 and 0.0008 min-1 for TBS at 37°C, and24 °C, respectively. For LB was 0.0030 min-1 at 37°C and for 0.0007 min-1 at 24°C. In bothmediums, an increase in the pH was observed from 7 to 8.5, which favors the equilibriumshifts from bicarbonate ions to carbonate ions.Understanding the growth kinetics provides insights into how L. sphaericus proliferatesunder different culture conditions, and they help to determine the most efficient conditionsfor bacterial growth and CaCO3 precipitation, contributing to the implementation of this ecofriendly and innovative technique in various engineering and construction applications andeven historical preservation projects.