The use of Gompertz models in growth analyses, and new Gompertz-model approach: An addition to the Unified-Richards family

<div><p>The Gompertz model is well known and widely used in many aspects of biology. It has been frequently used to describe the growth of animals and plants, as well as the number or volume of bacteria and cancer cells. Numerous parametrisations and re-parametrisations of varying usefulness are found in the literature, whereof the Gompertz-Laird is one of the more commonly used. Here, we review, present, and discuss the many re-parametrisations and some parameterisations of the Gompertz model, which we divide into <i>T</i>_<i>i</i> (type I)- and <i>W</i>₀ (type II)-forms. In the <i>W</i>₀-form a starting-point parameter, meaning birth or hatching value (<i>W</i>₀), replaces the inflection-time parameter (<i>T</i>_<i>i</i>). We also propose new “unified” versions (U-versions) of both the traditional <i>T</i>_<i>i</i> -form and a simplified <i>W</i>₀-form. In these, the growth-rate constant represents the relative growth rate instead of merely an unspecified growth coefficient. We also present U-versions where the growth-rate parameters return absolute growth rate (instead of relative). The new U-Gompertz models are special cases of the Unified-Richards (U-Richards) model and thus belong to the Richards family of U-models. As U-models, they have a set of parameters, which are comparable across models in the family, without conversion equations. The improvements are simple, and may seem trivial, but are of great importance to those who study organismal growth, as the two new U-Gompertz forms give easy and fast access to all shape parameters needed for describing most types of growth following the shape of the Gompertz model.</p></div

Optimisation of biodegradation conditions for cyanide removal by Serratia marcescens strain AQ07 using one-factor-at-a-time technique and response surface methodology

Gold mining companies are known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major environmental issue. Serratia marcescens strain AQ07 was found to have cyanide-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time and response surface methodology. Cyanide degradation corresponded with growth rate with a maximum growth rate of 16.14 log cfu/mL on day 3 of incubation. Glucose and yeast extract are suitable carbon and nitrogen sources. Six parameters including carbon and nitrogen sources, pH, temperature, inoculum size and cyanide concentration were optimised. In line with the central composite design of response surface methodology, cyanide degradation was optimum at glucose concentration 5.5 g/L, yeast extract 0.55 g/L, pH 6, temperature 32.5 °C, inoculum size 20 % and cyanide concentration 200 mg/L. It was able to stand cyanide toxicity of up to 700 mg/L, which makes it an important candidate for bioremediation of cyanide. The bacterium was observed to degrade 95.6 % of 200 mg/L KCN under the optimised condition. Bacteria are reported to degrade cyanide into ammonia, formamide or formate and carbon dioxide, which are less toxic by-products. These bacteria illustrate good cyanide degradation potential that can be harnessed in cyanide remediation