Editing Bacterial growth (section)

==Environmental conditions==
{{Expand section|date=October 2016}}
<!-- Section needs to be completed or more well rounded and reviewed by someone knowledgeable in the field so it's not missing any key important points. (2016-10-08) -->

Environmental factors influence rate of bacterial growth such as acidity (pH), temperature, water activity, macro and micro nutrients, oxygen levels, and toxins. Conditions tend to be relatively consistent between bacteria with the exception of [[extremophiles]]. Bacterium have optimal growth conditions under which they thrive, but once outside of those conditions the stress can result in either reduced or stalled growth, dormancy (such as formation [[bacterial spore|spores]]), or death. Maintaining sub-optimal growth conditions is a key principle to [[food preservation]].

===Temperature===
Low temperatures tend to reduce growth rates which has led to refrigeration being instrumental in food preservation. Depending on temperature, bacteria can be classified as:

* '''Psychrophiles'''
[[Psychrophile]]s are extremophilic cold-loving bacteria or archaea with an optimal temperature for growth at about 15&nbsp;°C or lower (maximal temperature for growth at 20&nbsp;°C, minimal temperature for growth at 0&nbsp;°C or lower). Psychrophiles are typically found in Earth's extremely cold ecosystems, such as polar ice-cap regions, permafrost, polar surface, and deep oceans.<ref>{{cite journal | vauthors = Moyer CL, Morita RY | title = Psychrophiles and Psychrotrophs | journal = eLS |date=16 April 2007 |doi=10.1002/9780470015902.a0000402.pub2| isbn = 9780470016176 }}</ref>
* '''Mesophiles'''
[[Mesophile]]s are bacteria that thrive at moderate temperatures, growing best between 20° and 45&nbsp;°C. These temperatures align with the natural body temperatures of humans, which is why many human pathogens are mesophiles.<ref>{{Cite web|url=https://www.biology-online.org/dictionary/Mesophile|title=Mesophile | work = Biology-Online Dictionary |language=en|access-date=2018-02-06}}</ref>
* '''Thermophiles'''
Survive under temperatures of 45–80&nbsp;°C.<ref>{{cite journal | vauthors = Bergey DH | title = Thermophilic Bacteria | journal = Journal of Bacteriology | volume = 4 | issue = 4 | pages = 301–306 | date = July 1919 | pmid = 16558843 | pmc = 378811 | doi = 10.1128/jb.4.4.301-306.1919 }}</ref>

===Acidity===
Optimal acidity for bacteria tends to be around pH 6.5 to 7.0 (neutral), those living in lesser pH being [[acidophiles]] and higher [[alkalophiles]]. Some bacteria can change the pH such as by excreting acid resulting in sub-optimal conditions.<ref>{{cite web| vauthors = Blamire J |title=Effect of pH on Growth Rate|url=http://www.brooklyn.cuny.edu/bc/ahp/CellBio/Growth/MGpH.html|website=Brooklyn College|access-date=8 October 2016}}</ref>

===Water activity===
{{See also|Water activity}}

===Oxygen===
Bacteria can be [[aerobes]] or [[anaerobes]]. Depending on the degree of oxygen required bacteria can fall into the following classes:

# facultative-anaerobes-ie aerotolerant absence or minimal oxygen required for their growth
# obligate-anaerobes grow only in complete absence of oxygen
# facultative aerobes-can grow either in presence or minimal oxygen
# obligate aerobes-grow only in the presence of oxygen

===Micronutrients===
Ample nutrients

{{See also|Iron#Biological and pathological role}}

===Toxic compounds===
Toxic compounds such as [[ethanol]] can hinder growth or kill bacteria. This is used beneficially for [[disinfection]] and in [[preservative|food preservation]].