# Microbial Bioremediation and Biodegradation of Petroleum Products--A Mini Review
## 3 Microbial Diversity and Ecology
### Microbial Influential Factors
#### 3.2.5 pH  
The pH of the environment can also influence biological processes, e.g., Enzyme activities, catalytic reaction equilibrium, and cell membrane transport. Its variability must be taken into account, enhancing biological treatment approaches. Unlike aquatic ecosystems, most heterotrophic bacteria grow in a neutral to alkaline pH, and soil acidity can also vary from pH 2.5 to pH 11 in alkaline deserts. However, heterotrophic bacteria and fungi generally favor a near-neutral pH, although fungi can tolerate acidic conditions. Studies have also shown that pH 6.5 leads to microbial mineralization of octadecane and naphthalene [35]. The studies again showed that while the mineralization rate of naphthalene was unchanged when the pH was increased from 6.5 to 8.0, octadecane mineralization increased remarkably. Pseudomonas aeruginosa biodegradable crude oil to the highest degree in the water and mud samples, with pH values of 8.0 and 7.8, respectively [44]. Moreover, [PERSON] [45] found that the most suitable pH for the degradation of all soil pH is 7.5, and the degradation of phenanthrene in liquid media at pH 6.5-7.0 was beneficial [46].  
Biological treatment is usually about removing pollutants and toxins from the confined environment with microorganisms. bioreactors have been used to treat contaminated PAH and remove oxy-PAHs such as PAH ketones, quinones, and coumarins [47]. These compounds can be configured by chemical oxidation and phototransformation of PAHs and are formed via the metabolism of microorganisms to PAHs. The availability of water for microbial growth and metabolic processes can affect the biodegradation of hydrocarbons in terrestrial ecosystems. Biodegradation reaches its optimal level with 30 to 90% water saturation in the oil sludge [35]. Tar globule deposits could also limit microbial degradation to hydrocarbons. In addition, a link exists between the rate of mineralization and the salinity of PAHs in estuarine sediments. Studies reported an overall decrease in microbial metabolic rates when salinity increased to 3.3-28.4%, leading to the evaporation of salt ponds [35; 37]. Therefore, salinity affects biodegradation as it affects microbial diversity and growth [48]. Moreover, it has an unfavorable effect on some necessary enzymes involved in the breakdown of hydrocarbons [49]. Table 3 shows the microbial factors influencing the biological degradation of mineral oil products.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Condition** \\ \hline Pressure & Monitoring was done at 10 atm and 495 or 500 atm for the breakdown of hydrocarbon feedstock by a culture broth of deep sea sediment bacteria. \\  & The hydrocarbon breakdown rate decreased with increasing salinity \\ Salinity & between 3.3\% and 28.4\%, and the findings were linked to a gradual decline \\  & in microbial metabolism activities. \\  & Due to their capacity to boost bioavailability, research into bio-surfactants \\  & and microorganisms that produce them has been done on a number of \\ Bioavailability & Surfactant application in oil-contaminated locations may have a neutral, inhibiting, or stimulatory effect on bacteria decomposing oil molecules. \\  & The degree of alkane degradation is impacted by the introduction of \\  & foreign oil spill dispersants or non-surfactants. \\  & In an aquatic setting, the water potential can be as low as \(-0.98\) and as high \\  & as 0.0–0.99 in soil. \\  & The best rate for oil sludge biodegradation in soil is between 30\% and 90\% of saturated water. \\  & Extreme pH range in soil: mine soil \(-2.5\), alkaline desert \(-11.0\). \\  & Most heterotrophic fungi and bacteria favour a pH neutral. \\ \hline \end{tabular}
\end{table}
Table 3: Influential factors of microbial ecology adapted and modified from [PERSON] [50] and [PERSON] & [PERSON] [51].